Cannabis and schizophrenia: model projections of the impact of the rise in cannabis use on historical and future trends in schizophrenia in England and Wales

Predictive factors and symptom severity spectrum in adult schizophrenia: Potential insights for improved management and adequate care

Schizophrenia is one of the most disabling psychiatric disorders characterized by positive (hallucinations, delusions, formal thinking disorder) and negative symptoms (anhedonia, lack of speech and motivation). The present study aimed to identify the predictive factors of schizophrenia in adults, and potential differences in the environment of origin, sex, levels of occupational stress, intellectual level, marital status and age of onset of the disease depending on the severity of symptoms using analysis of data collected from 120 patients with a diagnosis of schizophrenia. The study was conducted at the 'Prof. Dr. Alexandru Obregia' Clinical Psychiatric Hospital in Bucharest and included adult patients hospitalized between March 2018 and January 2021 diagnosed with schizophrenia and evaluated by general clinical examination, psychiatric, neurological and psychological evaluation. Results revealed that robust predictors of mild and moderate symptoms were affective symptoms, heredo-collateral history of schizophrenia, late onset, the presence of positive and negative symptoms, substance abuse, stress and marital status, unmarried, lower IQ and mental deficiency. For moderate-severe and severe symptoms, predictors were affective symptoms, heredo-collateral history of schizophrenia and affective disorders, substance abuse, stress, borderline IQ and mild mental deficiency. The present results can be used for further development of psychopharmacological management of schizophrenia.

The Role of Social Deprivation and Cannabis Use in Explaining Variation in the Incidence of Psychotic Disorders: Findings From the EU-GEI Study

BACKGROUND AND HYPOTHESIS

Recent findings suggest the incidence of first-episode psychotic disorders (FEP) varies according to setting-level deprivation and cannabis use, but these factors have not been investigated together. We hypothesized deprivation would be more strongly associated with variation in FEP incidence than the prevalence of daily or high-potency cannabis use between settings.

STUDY DESIGN

We used incidence data in people aged 18-64 years from 14 settings of the EU-GEI study. We estimated the prevalence of daily and high-potency cannabis use in controls as a proxy for usage in the population at-risk; multiple imputations by chained equations and poststratification weighting handled missing data and control representativeness, respectively. We modeled FEP incidence in random intercepts negative binomial regression models to investigate associations with the prevalence of cannabis use in controls, unemployment, and owner-occupancy in each setting, controlling for population density, age, sex, and migrant/ethnic group.

STUDY RESULTS

Lower owner-occupancy was independently associated with increased FEP (adjusted incidence rate ratio [aIRR]: 0.76, 95% CI: 0.61-0.95) and non-affective psychosis incidence (aIRR: 0.68, 95% CI: 0.55-0.83), after multivariable adjustment. Prevalence of daily cannabis use in controls was associated with the incidence of affective psychoses (aIRR: 1.53, 95% CI: 1.02-2.31). We found no association between FEP incidence and unemployment or high-potency cannabis use prevalence. Sensitivity analyses supported these findings.

CONCLUSIONS

Lower setting-level owner-occupancy and increased prevalence of daily cannabis use in controls independently contributed to setting-level variance in the incidence of different psychotic disorders. Public health interventions that reduce exposure to these harmful environmental factors could lower the population-level burden of psychotic disorders.

Assessing evidence supporting cannabis harm reduction practices for adolescents at clinical high-risk for psychosis: a review and clinical implementation tool

Cannabis use is consistently associated with both increased incidence of frank psychotic disorders and acute exacerbations of psychotic symptoms in healthy individuals and people with psychosis spectrum disorders. Although there is uncertainty around causality, cannabis use may be one of a few modifiable risk factors for conversion to psychotic disorders in individuals with Clinical High Risk for Psychosis (CHR-P) syndromes, characterized by functionally impairing and distressing subthreshold psychotic symptoms. To date, few recommendations beyond abstinence to reduce adverse psychiatric events associated with cannabis use have been made. This narrative review synthesizes existing scientific literature on cannabis' acute psychotomimetic effects and epidemiological associations with psychotic disorders in both CHR-P and healthy individuals to bridge the gap between scientific knowledge and practical mental health intervention. There is compelling evidence for cannabis acutely exacerbating psychotic symptoms in CHR-P, but its impact on conversion to psychotic disorder is unclear. Current evidence supports a harm reduction approach in reducing frequency of acute psychotic-like experiences, though whether such interventions decrease CHR-P individuals' risk of conversion to psychotic disorder remains unknown. Specific recommendations include reducing frequency of use, lowering delta-9-tetrahydrocannabinol content in favor of cannabidiol-only products, avoiding products with inconsistent potency like edibles, enhancing patient-provider communication about cannabis use and psychotic-like experiences, and utilizing a collaborative and individualized therapeutic approach. Despite uncertainty surrounding cannabis' causal association with psychotic disorders, cautious attempts to reduce acute psychosis risk may benefit CHR-P individuals uninterested in abstinence. Further research is needed to clarify practices associated with minimization of cannabis-related psychosis risk.

A network approach to relationships between cannabis use characteristics and psychopathology in the general population

Cannabis use characteristics, such as earlier initiation and frequent use, have been associated with an increased risk for developing psychotic experiences and psychotic disorders. However, little is known how these characteristics relate to specific aspects of sub-clinical psychopathology in the general population. Here, we explore the relationships between cannabis use characteristics and psychopathology in a large general population sample (N = 2,544, mean age 29.2 years, 47% women) by employing a network approach. This allows for the identification of unique associations between two cannabis use characteristics (lifetime cumulative frequency of cannabis use, age of cannabis use initiation), and specific psychotic experiences and affective symptoms, while controlling for early risk factors (childhood trauma, urban upbringing). We found particularly pronounced unique positive associations between frequency of cannabis use and specific delusional experiences (persecutory delusions and thought broadcasting). Age of cannabis use initiation was negatively related to visual hallucinatory experiences and irritability, implying that these experiences become more likely the earlier use is initiated. Earlier initiation, but not lifetime frequency of cannabis use, was related to early risk factors. These findings suggest that cannabis use characteristics may contribute differentially to risk for specific psychotic experiences and affective symptoms in the general population.

Changes in alcohol and cigarette consumption in response to medical and recreational cannabis legalization: Evidence from U.S. state tax receipt data

BACKGROUND

Whether medical or recreational cannabis legalization impacts alcohol or cigarette consumption is a key question as cannabis policy evolves, given the adverse health effects of these substances. Relatively little research has examined this question. The objective of this study was to examine whether medical or recreational cannabis legalization was associated with any change in state-level per capita alcohol or cigarette consumption.

METHODS

Dependent variables included per capita consumption of alcohol and cigarettes from all 50 U.S. states, estimated from state tax receipts and maintained by the Centers for Disease Control and National Institute for Alcohol Abuse and Alcoholism, respectively. Independent variables included indicators for medical and recreational legalization policies. Three different types of indicators were separately used to model medical cannabis policies. Indicators for the primary model were based on the presence of active medical cannabis dispensaries. Secondary models used indicators based on either the presence of a more liberal medical cannabis policy ("non-medicalized") or the presence of any medical cannabis policy. Difference-in-difference regression models were applied to estimate associations for each type of policy.

RESULTS

Primary models found no statistically significant associations between medical or recreational cannabis legalization policies and either alcohol or cigarette sales per capita. In a secondary model, both medical and recreational policies were associated with significantly decreased per capita cigarette sales compared to states with no medical cannabis policy. However, post hoc analyses demonstrated that these reductions were apparent at least two years prior to policy adoption, indicating that they likely result from other time-varying characteristics of legalization states, rather than cannabis policy.

CONCLUSION

We found no evidence of a causal association between medical or recreational cannabis legalization and changes in either alcohol or cigarette sales per capita.

Using the pharmacy retail model to examine perceptions and biases of a UK population sample towards regulation of specific psychoactive drugs

Background:

Contemporary research indicates that the legal classifications of cannabis (Schedule 2, Class B), 3,4-methylenedioxymethamphetamine (MDMA) (Schedule 1, Class A) and psilocybin (Schedule 1, Class A) in the United Kingdom are not entirely based on considerations of harm and therapeutic utility. The legal classifications of the substances discussed are typically determined by legislators such as Parliament and, therefore, may be a reflection of the views or perceived views of the general public.

Objective:

The aim of the study was to provide an indication of the underlying psychology regarding the legislated sale of alcohol, tobacco, cannabis, MDMA and psilocybin in pharmacies according to a UK general population sample.

Methods:

A sample of 105 UK nationals was selected for the survey. Participants were asked questions on perceived relative harm of the five substances. After viewing contemporary information on reported relative harm and therapeutic applications, the participants were asked questions related to using the pharmacy retail model for the sale of the substances discussed. Participants who opposed the substances being sold primarily in pharmacies were asked to explain their rationale according to a predetermined list of options for each of the five drugs. Participants were also asked whether they consider it a human right to be legally permitted to consume the substances.

Results:

The participants' perceptions of relative harm (tobacco > MDMA > psilocybin > alcohol > cannabis) were not in agreement with the relative harm reported in the literature (alcohol > tobacco > cannabis > MDMA > psilocybin). Principal objections to the currently illicit substances being legally available in pharmacies include it sending the wrong message; it feels wrong; it is too dangerous; disliking the smell of cannabis; disapproval of the people; and not liking the idea of people using psychoactive drugs for entertainment or to have mystical/religious experiences. Overall, the participants determined that being legally permitted to consume the substances discussed is an issue of relevance to human rights. A majority of the male participants concluded that being legally permitted to consume alcohol, tobacco, cannabis and Psilocybe mushrooms is a human right in contrast to the majority of female participants who solely considered alcohol consumption to be a human right.

Conclusions:

The data suggest that the legal classifications may not simply be based on considerations of harm. Misperceptions of the dangers, biases and non-health-related aversions likely contribute to the continuation of policies that do not reflect the state of scientific research.

Genetic Predisposition vs Individual-Specific Processes in the Association Between Psychotic-like Experiences and Cannabis Use

Importance

Previous research indicates that cannabis use is associated with psychotic-like experiences (PLEs). However, it is unclear whether this association results from predispositional (ie, shared genetic) factors or individual-specific factors (eg, causal processes, such as cannabis use leading to PLEs).

Objectives

To estimate genetic and environmental correlations between cannabis use and PLEs, and to examine PLEs in twin and nontwin sibling pairs discordant for exposure to cannabis use to disentangle predispositional from individual-specific effects.

Design, Setting, and Participants

In this cross-sectional analysis, diagnostic interviews and self-reported data were collected from 2 separate population-based samples of twin and nontwin sibling pairs. Data from the Human Connectome Project were collected between August 10, 2012, and September 29, 2015, and data from the Australian Twin Registry Cohort 3 (ATR3) were collected between August 1, 2005, and August 31, 2010. Data were analyzed between August 17, 2017, and July 6, 2018. The study included data from 1188 Human Connectome Project participants and 3486 ATR3 participants, totaling 4674 participants.

Main Outcomes and Measures

Three cannabis-involvement variables were examined: frequent use (ie, ≥100 times), a DSM-IV lifetime cannabis use disorder diagnosis, and current cannabis use. Genetic and environmental correlations between cannabis involvement and PLEs were estimated. Generalized linear mixed models examined PLE differences in twin and nontwin sibling pairs discordant for cannabis use.

Results

Among the 4674 participants, the mean (SD) age was 30.5 (3.2) years, and 2923 (62.5%) were female. Data on race/ethnicity were not included as a covariate owing to lack of variability within the ATR3 sample; among the 1188 participants in the Human Connectome Project, 875 (73.7%) were white. Psychotic-like experiences were associated with frequent cannabis use (β = 0.11; 95% CI, 0.08-0.14), cannabis use disorder (β = 0.13; 95% CI, 0.09-0.16), and current cannabis use (β = 0.07; 95% CI, 0.04-0.10) even after adjustment for covariates. Correlated genetic factors explained between 69.2% and 84.1% of this observed association. Within discordant pairs of twins/siblings (Npairs, 308-324), Psychotic-like experiences were more common in cannabis-exposed individuals compared with their relative who used cannabis to a lesser degree (β ≥ .23, P < .05; eg, frequent and infrequent cannabis-using relatives significantly differed, z = -5.41; P < .001).

Conclusions and Relevance

Despite the strong contribution of shared genetic factors, frequent and problem cannabis use also appears to be associated with PLEs via person-specific pathways. This study's findings suggest that policy discussions surrounding legalization should consider the influence of escalations in cannabis use on traitlike indices of vulnerability, such as PLEs, which could contribute to pervasive psychological and interpersonal burden.

Mental Health-related Emergency Department Visits Associated With Cannabis in Colorado

BACKGROUND

Cannabis legalization in Colorado resulted in increased cannabis-associated health care utilization. Our objective was to examine cooccurrence of cannabis and mental health diagnostic coding in Colorado emergency department (ED) discharges and replicate the study in a subpopulation of ED visits where cannabis involvement and psychiatric diagnosis were confirmed through medical review.

METHODS

We collected statewide ED International Classification of Diseases, 9th Revision, Clinical Modification diagnoses from the Colorado Hospital Association and a subpopulation of ED visits from a large, academic hospital from 2012 to 2014. Diagnosis codes identified visits associated with mental health and cannabis. Codes for mental health conditions and cannabis were confirmed by manual records review in the academic hospital subpopulation. Prevalence ratios (PRs) of mental health ED discharges were calculated to compare cannabis-associated visits to those without cannabis. Rates of mental health and cannabis-associated ED discharges were examined over time.

RESULTS

Statewide data demonstrated a fivefold higher prevalence of mental health diagnoses in cannabis-associated ED visits (PR = 5.35, 95% confidence interval [CI], 5.27-5.43) compared to visits without cannabis. The hospital subpopulation supported this finding with a fourfold higher prevalence of psychiatric complaints in cannabis attributable ED visits (PR = 4.87, 95% CI = 4.36-5.44) compared to visits not attributable to cannabis. Statewide rates of ED visits associated with both cannabis and mental health significantly increased from 2012 to 2014 from 224.5 to 268.4 per 100,000 (p < 0.0001).

CONCLUSIONS

In Colorado, the prevalence of mental health conditions in ED visits with cannabis-associated diagnostic codes is higher than in those without cannabis. There is a need for further research determining if these findings are truly attributed to cannabis or merely coincident with concurrent increased use and availability.

Interactions between cannabis and schizophrenia in humans and rodents

In this review, we provide an overview of the relationship between cannabis use and the development of schizophrenia, using both animal and human studies. We further discuss the potential neural mechanism that may mediate the relationship between cannabis use and schizophrenia symptoms. We finally provide clinical implications and future studies that can further elucidate the relationship between cannabis and schizophrenia.

Cannabis use and psychosis: the origins and implications of an association

Evidence for the effectiveness of treatment or secondary prevention of psychotic illness such as schizophrenia is often disappointing. This situation reflects our limited understanding of the aetiology of psychosis. There is good evidence that both genetic and environmental factors are implicated but the precise identity of these is unclear. Cannabis use is one candidate as a possible, modifiable environmental influence on both incidence and prognosis of psychosis. Evidence supporting this candidature is exclusively observational, and its strength has perhaps been overestimated and problems related to its interpretation underestimated by some. Nevertheless the possibility that cannabis does cause psychosis remains. Because of this, and because there are other good public health reasons to prevent cannabis use, interventions targeting use need to be evaluated. This evaluation, along with other imaginative approaches to future research, is needed to further our understanding of the determinants of mental illness and how we can most effectively improve the population's mental health.

Age at first tobacco use and risk of subsequent psychosis-related outcomes: A birth cohort study

OBJECTIVE

Compared to the substantial body of research examining links between cannabis use and psychosis, there has been relatively little attention to the role of tobacco as a potential risk factor for psychosis. This study explored the association between age at first tobacco use and psychosis-related outcomes in a birth cohort.

METHOD

This study is based on a large birth cohort (the Mater-University Study of Pregnancy). At approximately 21 years of age, cohort members (N = 3752) were assessed for three psychosis-related outcomes (International Classification of Diseases non-affective psychosis, the presence of any hallucination and total count of delusional-like experiences) with the Composite International Diagnostic Interview and the Peters Delusional Inventory. Associations between age at first tobacco use and psychosis-related outcomes were examined using logistic regression in a model (a) adjusted for sex and age and (b) in a second model excluding all respondents who had a history of past problematic and current cannabis use.

RESULTS

When adjusted for age and sex, those who commenced tobacco at 15 years of age or younger were significantly more likely to (a) have non-affective psychosis, (b) be in the highest quartile of total score of the Peters Delusional Inventory and (c) report hallucinations. After excluding all those with a history of a cannabis use disorder, or who were current (last month) cannabis users, a significant association between age at first tobacco use and the presence of hallucinations persisted.

CONCLUSION

There is an association between age at first tobacco use and subsequent psychosis-related outcomes in young adults. While the findings cannot be used to deduce causality, it adds weight to the hypothesis that early tobacco use may contribute to the risk of developing psychosis-related outcomes.

Limitations to the Dutch cannabis toleration policy: Assumptions underlying the reclassification of cannabis above 15% THC

The Netherlands has seen an increase in Δ9-tetrahydrocannabinol (THC) concentrations from approximately 8% in the 1990s up to 20% in 2004. Increased cannabis potency may lead to higher THC-exposure and cannabis related harm. The Dutch government officially condones the sale of cannabis from so called 'coffee shops', and the Opium Act distinguishes cannabis as a Schedule II drug with 'acceptable risk' from other drugs with 'unacceptable risk' (Schedule I). Even in 1976, however, cannabis potency was taken into account by distinguishing hemp oil as a Schedule I drug. In 2011, an advisory committee recommended tightening up legislation, leading to a 2013 bill proposing the reclassification of high potency cannabis products with a THC content of 15% or more as a Schedule I drug. The purpose of this measure was twofold: to reduce public health risks and to reduce illegal cultivation and export of cannabis by increasing punishment. This paper focuses on the public health aspects and describes the (explicit and implicit) assumptions underlying this '15% THC measure', as well as to what extent these are supported by scientific research. Based on scientific literature and other sources of information, we conclude that the 15% measure can provide in theory a slight health benefit for specific groups of cannabis users (i.e., frequent users preferring strong cannabis, purchasing from coffee shops, using 'steady quantities' and not changing their smoking behaviour), but certainly not for all cannabis users. These gains should be weighed against the investment in enforcement and the risk of unintended (adverse) effects. Given the many assumptions and uncertainty about the nature and extent of the expected buying and smoking behaviour changes, the measure is a political choice and based on thin evidence.

Does Cannabis Cause, Exacerbate or Ameliorate Psychiatric Disorders? An Oversimplified Debate Discussed

There have been extensive policy shifts in the legality of recreational and therapeutic use of cannabis in the United States, as well as a steady increase in the number of people using the drug on a regular basis. Given these rapid societal changes, defining what is known scientifically about the consequences of cannabis use on mental health takes on added public health significance. The purpose of this circumspectives piece is to discuss evidence of cannabis' effects on two psychiatric conditions: post-traumatic stress disorder and psychotic disorders. Dr Haney and Dr Evins will discuss two viewpoints regarding the benefit and harm of cannabis use for these conditions, while outlining what remains unproven and requires further testing to move the field forward.

Long-term risk factors for substance-induced and primary psychosis after release from prison. A longitudinal study of substance users

PURPOSE

The purpose of this study was to determine long-term risk factors for substance-induced and primary psychosis after release from prison.

MATERIAL

We used a longitudinal register-based cohort study combining European version of Addiction Severity Index (Europ-ASI) interviews and the Swedish inpatient register. The study included 6217 individuals who were in the Swedish criminal justice system from 2001 to 2006.

MEASUREMENTS

The outcomes were substance-induced and primary psychosis as defined by the International Classification of Disease - 10th version. All variables for estimating baseline risk were drawn from the Europ-ASI interview, and included information on substance use, demographics and health. The interview database and the inpatient register were coupled, and groups were compared by using tests of significance and logistic regression.

RESULTS

Polydrug use was the strongest predictor for substance induced psychosis (OR=9.55, 95% CI 3.42-26.67), but all substances imposed an increased risk. Previous psychiatric hospitalization and non-drug related hallucinations were significant, but weaker, risk factors. The only substance variable that predicted primary psychosis was cannabis (OR=2.62, 95% CI 1.39-4.96), but previous psychiatric hospitalization (OR=3.22, 95% CI 2.27-4.54) and non-drug related hallucinations (OR=4.00, 95% CI 2.82-5.67) were even stronger predictors.

CONCLUSIONS

Cannabis use was a risk factor for primary psychosis, but other health related individual risk factors were even more important. Polydrug use was the strongest risk factor for substance-induced psychosis.

What has research over the past two decades revealed about the adverse health effects of recreational cannabis use?

AIMS

To examine changes in the evidence on the adverse health effects of cannabis since 1993.

METHODS

A comparison of the evidence in 1993 with the evidence and interpretation of the same health outcomes in 2013.

RESULTS

Research in the past 20 years has shown that driving while cannabis-impaired approximately doubles car crash risk and that around one in 10 regular cannabis users develop dependence. Regular cannabis use in adolescence approximately doubles the risks of early school-leaving and of cognitive impairment and psychoses in adulthood. Regular cannabis use in adolescence is also associated strongly with the use of other illicit drugs. These associations persist after controlling for plausible confounding variables in longitudinal studies. This suggests that cannabis use is a contributory cause of these outcomes but some researchers still argue that these relationships are explained by shared causes or risk factors. Cannabis smoking probably increases cardiovascular disease risk in middle-aged adults but its effects on respiratory function and respiratory cancer remain unclear, because most cannabis smokers have smoked or still smoke tobacco.

CONCLUSIONS

The epidemiological literature in the past 20 years shows that cannabis use increases the risk of accidents and can produce dependence, and that there are consistent associations between regular cannabis use and poor psychosocial outcomes and mental health in adulthood.

Effects of eye dominance (left vs. right) and cannabis use on intermanual coordination and negative symptoms in schizophrenia patients

Based on the previous findings, it has been assumed that in schizophrenia patients, eye dominance and cannabis use will affect negative symptoms and intermanual coordination (IMC), an index of interhemispheric communication. But eye dominance, specifically the clinical findings for it, has been neglected in schizophrenia research. We therefore investigated its effects in 52 right-handed (36 right-eyed and 16 left-eyed) and 51 left-handed (35 left-eyed and 16 right-eyed) schizophrenia in-patients without and with drug use. Eye dominance affected IMC in all schizophrenia patients. When comparing right- and left-handers, we found that this result was only significant in the right-handed patients and in the smaller subgroup without drug use. In the right-handers, left eye dominance-like left-handedness-was associated with higher values in IMC and less pronounced manifestation of negative symptoms, right eye dominance was not. Thus, left-eyed right-handers may be more closely related to left-handers than to right-handers. In accordance with the results from the literature, we suggest that these findings are due to better interhemispheric connections and less impairment of white matter structures, especially in right-hemispheric regions. Moreover, cannabis use was related to higher scores in IMC and less pronounced negative symptoms, but only in the right-eyed and not in the left-eyed right-handers or in the left-handers. Hence, differences in eye dominance and handedness may be partially responsible for different results in interhemispheric connections among cannabis users. In conclusion, both eye dominance and use of cannabis should be taken into account when assessing clinical symptoms in schizophrenia patients.

Cannabis and adolescent brain development

Heavy cannabis use has been frequently associated with increased rates of mental illness and cognitive impairment, particularly amongst adolescent users. However, the neurobiological processes that underlie these associations are still not well understood. In this review, we discuss the findings of studies examining the acute and chronic effects of cannabis use on the brain, with a particular focus on the impact of commencing use during adolescence. Accumulating evidence from both animal and human studies suggests that regular heavy use during this period is associated with more severe and persistent negative outcomes than use during adulthood, suggesting that the adolescent brain may be particularly vulnerable to the effects of cannabis exposure. As the endocannabinoid system plays an important role in brain development, it is plausible that prolonged use during adolescence results in a disruption in the normative neuromaturational processes that occur during this period. We identify synaptic pruning and white matter development as two processes that may be adversely impacted by cannabis exposure during adolescence. Potentially, alterations in these processes may underlie the cognitive and emotional deficits that have been associated with regular use commencing during adolescence.

Gone to Pot - A Review of the Association between Cannabis and Psychosis

Cannabis is the most commonly used illicit drug worldwide, with ~5 million daily users worldwide. Emerging evidence supports a number of associations between cannabis and psychosis/psychotic disorders, including schizophrenia. These associations-based on case-studies, surveys, epidemiological studies, and experimental studies indicate that cannabinoids can produce acute, transient effects; acute, persistent effects; and delayed, persistent effects that recapitulate the psychopathology and psychophysiology seen in schizophrenia. Acute exposure to both cannabis and synthetic cannabinoids (Spice/K2) can produce a full range of transient psychotomimetic symptoms, cognitive deficits, and psychophysiological abnormalities that bear a striking resemblance to symptoms of schizophrenia. In individuals with an established psychotic disorder, cannabinoids can exacerbate symptoms, trigger relapse, and have negative consequences on the course of the illness. Several factors appear to moderate these associations, including family history, genetic factors, history of childhood abuse, and the age at onset of cannabis use. Exposure to cannabinoids in adolescence confers a higher risk for psychosis outcomes in later life and the risk is dose-related. Individuals with polymorphisms of COMT and AKT1 genes may be at increased risk for psychotic disorders in association with cannabinoids, as are individuals with a family history of psychotic disorders or a history of childhood trauma. The relationship between cannabis and schizophrenia fulfills many but not all of the standard criteria for causality, including temporality, biological gradient, biological plausibility, experimental evidence, consistency, and coherence. At the present time, the evidence indicates that cannabis may be a component cause in the emergence of psychosis, and this warrants serious consideration from the point of view of public health policy.

The global epidemiology and contribution of cannabis use and dependence to the global burden of disease: results from the GBD 2010 study

AIMS

Estimate the prevalence of cannabis dependence and its contribution to the global burden of disease.

METHODS

Systematic reviews of epidemiological data on cannabis dependence (1990-2008) were conducted in line with PRISMA and meta-analysis of Observational Studies in Epidemiology (MOOSE) guidelines. Culling and data extraction followed protocols, with cross-checking and consistency checks. DisMod-MR, the latest version of generic disease modelling system, redesigned as a Bayesian meta-regression tool, imputed prevalence by age, year and sex for 187 countries and 21 regions. The disability weight associated with cannabis dependence was estimated through population surveys and multiplied by prevalence data to calculate the years of life lived with disability (YLDs) and disability-adjusted life years (DALYs). YLDs and DALYs attributed to regular cannabis use as a risk factor for schizophrenia were also estimated.

RESULTS

There were an estimated 13.1 million cannabis dependent people globally in 2010 (point prevalence0.19% (95% uncertainty: 0.17-0.21%)). Prevalence peaked between 20-24 yrs, was higher in males (0.23% (0.2-0.27%)) than females (0.14% (0.12-0.16%)) and in high income regions. Cannabis dependence accounted for 2 million DALYs globally (0.08%; 0.05-0.12%) in 2010; a 22% increase in crude DALYs since 1990 largely due to population growth. Countries with statistically higher age-standardised DALY rates included the United States, Canada, Australia, New Zealand and Western European countries such as the United Kingdom; those with lower DALY rates were from Sub-Saharan Africa-West and Latin America. Regular cannabis use as a risk factor for schizophrenia accounted for an estimated 7,000 DALYs globally.

CONCLUSION

Cannabis dependence is a disorder primarily experienced by young adults, especially in higher income countries. It has not been shown to increase mortality as opioid and other forms of illicit drug dependence do. Our estimates suggest that cannabis use as a risk factor for schizophrenia is not a major contributor to population-level disease burden.

Incidence trends of cannabis and cocaine use from periodic Spanish general population surveys: effect of standardizing results by age structure

AIMS

This study estimates life-time incidence trends of cannabis and cocaine use over 38 years from general population surveys of drug use (GPSDU) in Spain, taking into account changes of population age structure.

DESIGN

Periodic cross-sectional studies.

SETTING

Eight biennial GPSDU from 1995 to 2009 in Spain.

PARTICIPANTS

Interviewees aged 15-64 years who reported age of first ever cannabis and/or cocaine use between 10 and 64 years between 1971 and 2008.

MEASUREMENTS

Estimates of raw and standardized incidences were calculated as a weighted mean of the incidences from all surveys. Standardization was conducted to take into account changes of population age structure. Incidence trends were extracted applying weighted cubic smoothing splines to incidence estimates.

FINDINGS

For both substances, estimated raw incidence trends increased up until 2000 (rates of 11.5 ± 0.7 and 3.6 ± 0.5 per 1000, respectively, for cannabis and cocaine), and then decreased significantly (in 2008, 9.6 ± 1.2 and 2.7 ± 0.6, respectively). In contrast, standardized rates exhibit a steadily increasing trend up to 2000 (9.0 ± 0.6 and 2.8 ± 0.4), followed by a statistically non-significant increasing trend afterwards (in 2008, 9.5 ± 1.2 and 2.8 ± 0.6). The largest increases of incidence were observed in both male and female subjects aged 15-19 years.

CONCLUSIONS

Using data from Spanish general population surveys of drug use, an apparently decreasing trend of raw incidence rates in both cannabis and cocaine use from 2000 became non-decreasing trends when these rates were standardized. First experiences of cannabis and cocaine use in Spain occur mainly in younger ages (15-19 years).

Analysis of cannabis seizures in NSW, Australia: cannabis potency and cannabinoid profile

Recent analysis of the cannabinoid content of cannabis plants suggests a shift towards use of high potency plant material with high levels of Δ(9)-tetrahydrocannabinol (THC) and low levels of other phytocannabinoids, particularly cannabidiol (CBD). Use of this type of cannabis is thought by some to predispose to greater adverse outcomes on mental health and fewer therapeutic benefits. Australia has one of the highest per capita rates of cannabis use in the world yet there has been no previous systematic analysis of the cannabis being used. In the present study we examined the cannabinoid content of 206 cannabis samples that had been confiscated by police from recreational users holding 15 g of cannabis or less, under the New South Wales "Cannabis Cautioning" scheme. A further 26 "Known Provenance" samples were analysed that had been seized by police from larger indoor or outdoor cultivation sites rather than from street level users. An HPLC method was used to determine the content of 9 cannabinoids: THC, CBD, cannabigerol (CBG), and their plant-based carboxylic acid precursors THC-A, CBD-A and CBG-A, as well as cannabichromene (CBC), cannabinol (CBN) and tetrahydrocannabivarin (THC-V). The "Cannabis Cautioning" samples showed high mean THC content (THC+THC-A = 14.88%) and low mean CBD content (CBD+CBD-A = 0.14%). A modest level of CBG was detected (CBG+CBG-A = 1.18%) and very low levels of CBC, CBN and THC-V (<0.1%). "Known Provenance" samples showed no significant differences in THC content between those seized from indoor versus outdoor cultivation sites. The present analysis echoes trends reported in other countries towards the use of high potency cannabis with very low CBD content. The implications for public health outcomes and harm reduction strategies are discussed.

Effect of reclassification of cannabis on hospital admissions for cannabis psychosis: a time series analysis

BACKGROUND

The UK Misuse of Drugs Act (1971) divided controlled drugs into three groups A, B and C, with descending criminal sanctions attached to each class. Cannabis was originally assigned by the Act to Group B but in 2004, it was transferred to the lowest risk group, Group C. Then in 2009, on the basis of increasing concerns about a link between high strength cannabis and schizophrenia, it was moved back to Group B. The aim of this study is to test the assumption that changes in classification lead to changes in levels of psychosis. In particular, it explores whether the two changes in 2004 and 2009 were associated with changes in the numbers of people admitted for cannabis psychosis.

METHOD

An interrupted time series was used to investigate the relationship between the two changes in cannabis classification and their impact on hospital admissions for cannabis psychosis. Reflecting the two policy changes, two interruptions to the time series were made. Hospital Episode Statistics admissions data was analysed covering the period 1999 through to 2010.

RESULTS

There was a significantly increasing trend in cannabis psychosis admissions from 1999 to 2004. However, following the reclassification of cannabis from B to C in 2004, there was a significant change in the trend such that cannabis psychosis admissions declined to 2009. Following the second reclassification of cannabis back to class B in 2009, there was a significant change to increasing admissions.

CONCLUSION

This study shows a statistical association between the reclassification of cannabis and hospital admissions for cannabis psychosis in the opposite direction to that predicted by the presumed relationship between the two. However, the reasons for this statistical association are unclear. It is unlikely to be due to changes in cannabis use over this period. Other possible explanations include changes in policing and systemic changes in mental health services unrelated to classification decisions.

Stronger evidence is needed before accepting that cannabis plays an important role in the aetiology of schizophrenia in the population

Schizophrenia is a debilitating but poorly understood condition with very few known modifiable risk factors. Cannabis use can acutely induce psychotic experiences, but its causal relationship to schizophrenia is less well understood. Longitudinal cohort studies suggest that the association between cannabis and psychotic outcomes is not due to chance or reverse causation. However, the association could be due to bias or residual confounding. Methods that can test alternative explanations in greater depth are required. This is especially important as ecological studies have found little association between the increase in cannabis use over recent decades and incidence of psychotic disorders; public health models suggest that cannabis use may need to be treated and prevented in many thousands of users in order to prevent one case of schizophrenia. We believe that, while such uncertainty exists, there is a scientific duty to continue to investigate the role of cannabis in the aetiology of schizophrenia and that the policy case for considering cannabis exposure as a critical target for preventing schizophrenia is yet to be made. However, due to other evidence of the harms of cannabis use, this should not affect the public health message that cannabis can be harmful and that cannabis dependence should be prevented.

Drugs of abuse and increased risk of psychosis development

OBJECTIVE

There is considerable evidence to suggest that the abuse of illicit drugs, particularly cannabis and methamphetamine, has aetiological roles in the pathogenesis of psychosis and schizophrenia. Factors that may increase susceptibility to the propsychotic effects of these drugs include the age at which the abuse starts as well as family history of genetic polymorphisms relevant to the pathophysiology of this disorder. However, the neurobiological mechanisms involved in drug abuse-associated psychosis remain largely unclear.

METHODS AND RESULTS

This paper presents an overview of the available evidence, including clinical, animal model, and molecular studies, with a focus on brain regions and neurotransmitters systems, such as dopamine and glutamate, previously implicated in psychosis.

CONCLUSION

It is clear that further studies are urgently needed to provide a greater insight into the mechanisms that mediate the long-term and neurodevelopmental effects of cannabis and methamphetamine. A dialogue between basic science and clinical research may help to identify at-risk individuals and novel pathways for treatment and prevention.

Cannabis, schizophrenia and other non-affective psychoses: 35 years of follow-up of a population-based cohort

BACKGROUND

There is now strong evidence that cannabis use increases the risk of psychoses including schizophrenia, but the relationship between cannabis and different psychotic disorders, as well as the mechanisms, are poorly known. We aimed to assess types of psychotic outcomes after use of cannabis in adolescence and variation in risk over time.

METHOD

A cohort of 50 087 military conscripts with data on cannabis use in late adolescence was followed up during 35 years with regard to in-patient care for psychotic diagnoses.

RESULTS

Odds ratios for psychotic outcomes among frequent cannabis users compared with non-users were 3.7 [95% confidence interval (CI) 2.3-5.8] for schizophrenia, 2.2 (95% CI 1.0-4.7) for brief psychosis and 2.0 (95% CI 0.8-4.7) for other non-affective psychoses. Risk of schizophrenia declined over the decades in moderate users but much less so in frequent users. The presence of a brief psychosis did not increase risk of later schizophrenia more in cannabis users compared with non-users.

CONCLUSIONS

Our results confirm an increased risk of schizophrenia in a long-term perspective, although the risk declined over time in moderate users.

Incidence of schizophrenia and other psychoses in England, 1950-2009: a systematic review and meta-analyses

BACKGROUND

We conducted a systematic review of incidence rates in England over a sixty-year period to determine the extent to which rates varied along accepted (age, sex) and less-accepted epidemiological gradients (ethnicity, migration and place of birth and upbringing, time).

OBJECTIVES

To determine variation in incidence of several psychotic disorders as above.

DATA SOURCES

Published and grey literature searches (MEDLINE, PSycINFO, EMBASE, CINAHL, ASSIA, HMIC), and identification of unpublished data through bibliographic searches and author communication.

STUDY ELIGIBILITY CRITERIA

Published 1950-2009; conducted wholly or partially in England; original data on incidence of non-organic adult-onset psychosis or one or more factor(s) pertaining to incidence.

PARTICIPANTS

People, 16-64 years, with first -onset psychosis, including non-affective psychoses, schizophrenia, bipolar disorder, psychotic depression and substance-induced psychosis.

STUDY APPRAISAL AND SYNTHESIS METHODS

Title, abstract and full-text review by two independent raters to identify suitable citations. Data were extracted to a standardized extraction form. Descriptive appraisals of variation in rates, including tables and forest plots, and where suitable, random-effects meta-analyses and meta-regressions to test specific hypotheses; rate heterogeneity was assessed by the I²-statistic.

RESULTS

83 citations met inclusion. Pooled incidence of all psychoses (N = 9) was 31.7 per 100,000 person-years (95%CI: 24.6-40.9), 23.2 (95%CI: 18.3-29.5) for non-affective psychoses (N = 8), 15.2 (95%CI: 11.9-19.5) for schizophrenia (N = 15) and 12.4 (95%CI: 9.0-17.1) for affective psychoses (N = 7). This masked rate heterogeneity (I²: 0.54-0.97), possibly explained by socio-environmental factors; our review confirmed (via meta-regression) the typical age-sex interaction in psychosis risk, including secondary peak onset in women after 45 years. Rates of most disorders were elevated in several ethnic minority groups compared with the white (British) population. For example, for schizophrenia: black Caribbean (pooled RR: 5.6; 95%CI: 3.4-9.2; N = 5), black African (pooled RR: 4.7; 95%CI: 3.3-6.8; N = 5) and South Asian groups in England (pooled RR: 2.4; 95%CI: 1.3-4.5; N = 3). We found no evidence to support an overall change in the incidence of psychotic disorder over time, though diagnostic shifts (away from schizophrenia) were reported.

LIMITATIONS

Incidence studies were predominantly cross-sectional, limiting causal inference. Heterogeneity, while evidencing important variation, suggested pooled estimates require interpretation alongside our descriptive systematic results.

CONCLUSIONS AND IMPLICATIONS OF KEY FINDINGS

Incidence of psychotic disorders varied markedly by age, sex, place and migration status/ethnicity. Stable incidence over time, together with a robust socio-environmental epidemiology, provides a platform for developing prediction models for health service planning.

Popular intoxicants: what lessons can be learned from the last 40 years of alcohol and cannabis regulation?

In this paper we discuss the relative physical, psychological and social harms of the two most frequently used intoxicant drugs in the UK, namely cannabis and alcohol. Over the past 40 years, the use of both drugs has risen significantly with differential consequences. It is argued that increased policing of cannabis use under the current drug classification system will lead to increased criminalization of young people, but is unlikely to significantly reduce the rates of schizophrenia and psychosis. In comparison, increases in alcohol drinking are related to significant increases in liver cirrhosis hospital admissions and mortality, at a time when mortality rates from other major causes are on the decline. A recent expert-led comparison of the health and social harms to the user and to others caused by the most commonly used drugs in the UK showed alcohol to be more than twice as harmful as cannabis to users, and five times as harmful as cannabis to others. The findings underline the need for a coherent, evidence-based drugs policy that enables individuals to make informed decisions about the consequences of their drug use.

Hepatitis C prevalence in England remains low and varies by ethnicity: an updated evidence synthesis

BACKGROUND

Previous evidence synthesis estimates of Hepatitis C Virus (HCV) in England did not consider excess HCV risk in ethnic minority populations. We incorporate new information on HCV risk among non-injectors by ethnic group, and additional information on injecting prevalence in order to generate new and updated estimates of HCV prevalence risk in England for 2005.

METHODS

Bayesian evidence synthesis was used to combine multiple sources of data that directly or indirectly provide information on the populations at risk, or prevalence of HCV infection. HCV data were modelled by region, age group and sex as well as ethnicity for never-injectors and by injecting status (ex and current).

RESULTS

Overall HCV antibody prevalence in England was estimated at 0.67% [95% credible interval (95% CrI): 0.50-0.94] of those aged 15-59 years, or 203 000 (153 000, 286 000) individuals. HCV prevalence in never-injectors remains low, even after accounting for ethnicity, with a prevalence of 0.05% (95% CrI 0.03-0.10) in those of white/other ethnicity and 0.76% (0.48-1.23) in South Asians. Estimates are similar to 2003, although patterns of injecting drug use are different, with an older population of current injecting drug users and lower estimated numbers of ex-injectors, but higher HCV prevalence.

CONCLUSIONS

Incorporating updated information, including data on ethnicity and improved data on injectors, gave similar overall estimates of HCV prevalence in England. Further information on HCV in South Asians and natural history of injecting are required to reduce uncertainty of estimates. This method may be applied to other countries and settings.

Cannabis use in young people: the risk for schizophrenia

Cannabis is one of the most commonly used illicit drugs, and despite the widely held belief that it is a safe drug, its long-term use has potentially harmful consequences. To date, the research on the impact of its use has largely been epidemiological in nature and has consistently found that cannabis use is associated with schizophrenia outcomes later in life, even after controlling for several confounding factors. While the majority of users can continue their use without adverse effects, it is clear from studies of psychosis that some individuals are more vulnerable to its effects than others. In addiction, evidence from both epidemiological and animal studies indicates that cannabis use during adolescence carries particular risk. Further studies are warranted given the increase in the concentration of the main active ingredient (Δ(9)-tetrahydrocannabinol) in street preparations of cannabis and a decreasing age of first-time exposure to cannabis.

Incidence of hospitalised schizophrenia in Finland since 1980: decreasing and increasing again

BACKGROUND

It is suggested that the incidence of schizophrenia is decreasing. However, changes in the number of psychiatric beds available and diagnostic practice have not always been taken into account. We studied the annual first-admission rate (per 100,000) for schizophrenia (FARsch) during a rapid deinstitutionalisation period in Finland.

METHOD

From the National Finnish Hospital discharge register, we identified all 30,041, 15- to 64-year-old patients admitted for the first time with schizophrenia to hospitals in Finland between 1980 and 2003.

RESULTS

FARsch decreased from 56.39 in 1980 to 29.51 in 1991 and slightly increased thereafter. Changes in FARsch corresponded with changes in all admissions. FARsch was higher when using ICD-8, but lower when DSM-IIIR and ICD-10 were used.

CONCLUSION

Changes in the number of psychiatric beds available, admission policy and diagnostic practice may explain the majority of variations in FARsch. Possibly, increased use of illegal drugs and improved treatment of depression are reflected in the increase in FARsch.

The association between substance misuse and first-episode psychosis in a defined UK geographical area during the 1990s

OBJECTIVE

The aim of this study was to examine the prevalence of all substance use disorders (SUD) and cannabis-specific SUDs reported in two first-episode epidemiological studies, conducted in the same catchment area, 5 years apart.

METHODS

The prevalence of schizophrenia in Nottingham and Aetiology and Ethnicity of Schizophrenia and Other Psychoses studies included all people with a first-episode of psychosis between 1992 and 1994 and 1997 and 1999, respectively. Those individuals with a comorbid diagnosis of a SUD (ICD-10 harmful use or dependence) were identified.

RESULTS

An upward (but not statistically significant) trend in all SUDs was found for the first-episode study population as a whole, between the two cohorts (11.9-18.2%). When analysed by age, a significant increase in cannabis-specific SUDs was observed for all first-episode cases aged 16-29 between cohorts (3.2-10.6%). When analysed by age and gender, a significant increase in all SUDs was apparent for female first-episode patients aged 16-29 between cohorts (6.1-24.2%), this same increase was not seen in male patients.

CONCLUSIONS

Illegal drug misuse is common in patients with a first-episode of psychosis. However, most concerning is that when both age and gender are considered, females with a first-episode of psychosis aged 16-29 show a highly significant rise in the prevalence of all SUDs over the 1990s. More recent drug use data from England and Wales shows that the prevalence of drug use in the 21st century is declining; further epidemiological studies are required to determine whether this is also the case in young female first-episode psychosis populations.

Adolescent cannabis use and psychosis: epidemiology and neurodevelopmental models

Cannabis is one of the most widely used illicit drugs among adolescents, and most users first experiment with it in adolescence. Adolescence is a critical phase for brain development, characterized by neuronal maturation and rearrangement processes, such as myelination, synaptic pruning and dendritic plasticity. The endocannabinoid system plays an important role in fundamental brain developmental processes such as neuronal cell proliferation, migration and differentiation. Therefore changes in endocannabinoid activity during this specific developmental phase, induced by the psychoactive component of marijuana, Delta(9)-tetrahydrocannabinol, might lead to subtle but lasting neurobiological changes that can affect brain functions and behaviour. In this review, we outline recent research into the endocannabinoid system focusing on the relationships between adolescent exposure to cannabinoids and increased risk for certain neuropsychiatric diseases such as schizophrenia, as highlighted by both human and animal studies. Particular emphasis will be given to the possible mechanisms by which adolescent cannabis consumption could render a person more susceptible to developing psychoses such as schizophrenia.

How ideology shapes the evidence and the policy: what do we know about cannabis use and what should we do?

In the United Kingdom, as in many places, cannabis use is considered substantially within a criminal justice rather than a public health paradigm with prevention policy embodied in the Misuse of Drugs Act. In 2002 the maximum custodial sentence tariff for cannabis possession under the Act was reduced from 5 to 2 years. Vigorous and vociferous public debate followed this decision, centred principally on the question of whether cannabis use caused schizophrenia. It was suggested that new and compelling evidence supporting this hypothesis had emerged since the re-classification decision was made, meaning that the decision should be reconsidered. The re-classification decision was reversed in 2008. We consider whether the strength of evidence on the psychological harms of cannabis has changed substantially and discuss the factors that may have influenced recent public discourse and policy decisions. We also consider evidence for other harms of cannabis use and public health implications of preventing cannabis use. We conclude that the strongest evidence of a possible causal relation between cannabis use and schizophrenia emerged more than 20 years ago and that the strength of more recent evidence may have been overstated--for a number of possible reasons. We also conclude that cannabis use is almost certainly harmful, mainly because of its intimate relation to tobacco use. The most rational policy on cannabis from a public health perspective would seem to be one able to achieve the benefit of reduced use in the population while minimizing social and other costs of the policy itself. Prohibition, whatever the sentence tariff associated with it, seems unlikely to fulfil these criteria.

Efeitos comportamentais, cognitivos e psicofisiológicos dos canabinoides: relevância para a psicose e a esquizofrenia

Avanços recentes no conhecimento sobre a função do receptor de canabinoide renovaram o interesse na associação entre cannabis e psicose. Linhas convergentes de evidências sugerem que os canabinoides podem produzir uma ampla gama de sintomas transitórios positivos, negativos e cognitivos assemelhados aos de esquizofrenia. Os canabinoides também produzem alguns déficits psicofisiológicos sabidamente presentes na esquizofrenia. É igualmente claro que em indivíduos com um transtorno psicótico estabelecido, os canabinoides podem exacerbar sintomas, desencadear recaídas e ter consequências negativas no curso da doença. Evidências crescentes sugerem que a exposição precoce e pesada à cannabis pode aumentar o risco de se desenvolver um transtorno psicótico como a esquizofrenia. A relação entre exposição à cannabis e esquizofrenia preenche alguns, mas não todos os critérios usuais de causalidade. Porém, a maioria das pessoas que utilizam cannabis não desenvolve esquizofrenia e muitas pessoas diagnosticadas com esquizofrenia nunca utilizaram cannabis. Portanto, é provável que a exposição à cannabis seja uma "causa componente" que interage com outros fatores para "causar" esquizofrenia ou outro transtorno psicótico, mas não é nem necessária nem suficiente para fazê-lo sozinha. No entanto, na ausência de causas conhecidas da esquizofrenia e com as implicações de políticas de saúde pública, se tal vínculo for estabelecido, as causas componentes, tais como a exposição a canabinoide, devem continuar sendo um foco de estudos futuros. Finalmente, são necessárias mais pesquisas para identificar os fatores subjacentes à vulnerabilidade à psicose relacionada a canabinoide e para elucidar os mecanismos biológicos subjacentes a esse risco.

If cannabis caused schizophrenia--how many cannabis users may need to be prevented in order to prevent one case of schizophrenia? England and Wales calculations

BACKGROUND

We consider how many cannabis users may need to be prevented in order to prevent one case of schizophrenia or psychosis [defined as number needed to prevent (NNP)].

METHOD

Calculation for England and Wales using best available estimates of: incidence of schizophrenia; rates of heavy and light cannabis use; and risk that cannabis causes schizophrenia.

RESULTS

In men the annual mean NNP for heavy cannabis and schizophrenia ranged from 2800 [90% confidence interval (CI) 2018-4530] in those aged 20-24 years to 4700 (90% CI 3114-8416) in those aged 35-39. In women, mean NNP for heavy cannabis use and schizophrenia ranged from 5470 (90% CI 3640-9839) in those aged 25-29 to 10 870 (90% CI 6786-22 732) in 35-39-year-olds. Equivalent mean NNP for heavy cannabis use and psychosis were lower, from 1360 (90% CI 1007-2124) in men aged 20-24 and 2480 (90% CI 1408-3518) in women aged 16-19. The mean and median number of light cannabis users that would need to be prevented in order to prevent one case of schizophrenia or psychosis per year are four to five times greater than among heavy users.

CONCLUSIONS

The number of young people who need to be exposed to an intervention to generate NNP and prevent one case of schizophrenia will be even larger. The public health importance of preventing cannabis to reduce schizophrenia or psychosis remains uncertain. More attention should be given to testing the hypothesis that cannabis is related causally to psychotic outcomes, and to considering what strategies will be the most effective in reducing heavy cannabis use among young people.

Adverse health effects of non-medical cannabis use

For over two decades, cannabis, commonly known as marijuana, has been the most widely used illicit drug by young people in high-income countries, and has recently become popular on a global scale. Epidemiological research during the past 10 years suggests that regular use of cannabis during adolescence and into adulthood can have adverse effects. Epidemiological, clinical, and laboratory studies have established an association between cannabis use and adverse outcomes. We focus on adverse health effects of greatest potential public health interest-that is, those that are most likely to occur and to affect a large number of cannabis users. The most probable adverse effects include a dependence syndrome, increased risk of motor vehicle crashes, impaired respiratory function, cardiovascular disease, and adverse effects of regular use on adolescent psychosocial development and mental health.

Is the incidence of psychotic disorder in decline? Epidemiological evidence from two decades of research

BACKGROUND

It is unclear whether the incidence of first episode psychoses is in decline. We had the opportunity to determine whether incidence had changed over a 20-year period in a single setting, and test whether this could be explained by demographic or clinical changes.

METHODS

The entire population at-risk aged 16-54 in Nottingham over three time periods (1978-80, 1993-95 and 1997-99) were followed up. All participants presenting with an ICD-9/10 first episode psychosis were included. The remainder of the population at-risk formed the denominator. Standardized incidence rates were calculated at each time period with possible change over time assessed via Poisson regression. We studied six outcomes: substance-induced psychoses, schizophrenia, other non-affective psychoses, manic psychoses, depressive psychoses and all psychotic disorders combined.

RESULTS

Three hundred and forty-seven participants with a first episode psychosis during 1.2 million person-years of follow-up over three time periods were identified. The incidence of non-affective or affective psychoses had not changed over time following standardization for age, sex and ethnicity. We observed a linear increase in the incidence of substance-induced psychosis, per annum, over time (incidence rate ratios: 1.15; 95% CI 1.05-1.25). This could not be explained by longitudinal changes in the age, sex and ethnic structure of the population at-risk.

CONCLUSIONS

Our findings suggest psychotic disorders are not in decline, though there has been a change in the syndromal presentation of non-affective disorders, away from schizophrenia towards other non-affective psychoses. The incidence of substance-induced psychosis has increased, consistent with increases in substance toxicity over time, rather than changes in the prevalence or vulnerability to substance misuse. Increased clinical and popular awareness of substance misuse could also not be excluded.

Assessing the impact of cannabis use on trends in diagnosed schizophrenia in the United Kingdom from 1996 to 2005

A recent systematic review concluded that cannabis use increases risk of psychotic outcomes independently of confounding and transient intoxication effects. Furthermore, a model of the association between cannabis use and schizophrenia indicated that the incidence and prevalence of schizophrenia would increase from 1990 onwards. The model is based on three factors: a) increased relative risk of psychotic outcomes for frequent cannabis users compared to those who have never used cannabis between 1.8 and 3.1, b) a substantial rise in UK cannabis use from the mid-1970s and c) elevated risk of 20 years from first use of cannabis. This paper investigates whether this has occurred in the UK by examining trends in the annual prevalence and incidence of schizophrenia and psychoses, as measured by diagnosed cases from 1996 to 2005. Retrospective analysis of the General Practice Research Database (GPRD) was conducted for 183 practices in England, Wales, Scotland and Northern Ireland. The study cohort comprised almost 600,000 patients each year, representing approximately 2.3% of the UK population aged 16 to 44. Between 1996 and 2005 the incidence and prevalence of schizophrenia and psychoses were either stable or declining. Explanations other than a genuine stability or decline were considered, but appeared less plausible. In conclusion, this study did not find any evidence of increasing schizophrenia or psychoses in the general population from 1996 to 2005.

Should burden of disease estimates include cannabis use as a risk factor for psychosis?

Louise Degenhardt and colleagues discuss the evidence and the debate about whether Global Burden of Disease estimates should include cannabis use as a risk factor for psychosis.

Is socioeconomic status in early life associated with drug use? A systematic review of the evidence

AIM

To conduct a systematic review of longitudinal studies that examined the association between childhood socioeconomic status (SES) and illegal drug use in later life.

DESIGN AND METHODS

Systematic search with an agreed list of search items was used to identify all longitudinal population-based studies that examined the association between childhood SES and later drug use. These included MEDLINE (1966-2005), EMBASE (1990-2005), CINAHL (1982-2005) and PsychInfo (1806-2005), and specialist databases of the Lindesmith Library, Drugscope and Addiction Abstracts. Foreign-language papers were included. Abstracts were screened independently by two reviewers. If there was disagreement to accept or reject the abstract, then a third reviewer acted as arbiter. Data were extracted by one of the authors.

RESULTS

Eleven relevant papers were identified (two birth cohorts and nine papers on school-aged cohorts). There was consistent evidence to support an association between lower childhood SES and later drug use, primarily cannabis use. However, few studies examined cannabis dependence, and studies of more problematic forms of drug use gave contradictory results.

DISCUSSION AND CONCLUSIONS

We found consistent, though weak, evidence to support the assumption that childhood disadvantage is associated with later cannabis use. Further research is needed to clarify this issue and to inform future policies and public health messages.

The role of cannabis in cognitive functioning of patients with schizophrenia

RATIONALE

Cognitive deficits are commonly found both in patients with schizophrenia (SCH) and in people with cannabis use disorders (CUD). Surprisingly, some small recent studies reported better cognitive performance in SCH patients with comorbid cannabis use disorders (SCH + CUD) compared to other SCH patients.

OBJECTIVES

The aim of the present study was to investigate the residual impact of CUD and specific patterns of consumption on cognition in a larger sample of SCH + CUD patients.

METHODS

We administered a cognitive test battery to 34 SCH and 35 currently abstinent SCH + CUD patients. We explored the association between patterns of cannabis consumption and cognitive performance. Potential confounds with influence on cognitive ability were assessed and controlled for.

RESULTS

SCH + CUD patients had poorer academic achievements and lower vocabulary scores, but they performed better in tests of verbal and working memory, visuomotor speed and executive function (p < .05). More frequent cannabis use was associated with better performance in attention and working memory tasks.

CONCLUSIONS

Although our findings might be interpreted as beneficial effect of cannabis use on cognition in patients with schizophrenia, we favorise an alternative interpretation: in our view, the better cognitive functioning of SCH + CUD patients may rather reflect a relatively lower vulnerability to psychosis compared to the SCH group. Lower vulnerability may correspond to a higher level of functioning such as cognitive ability. This conclusion is consistent with the view of cannabis playing a critical role in the manifestation of psychosis in at least some of the SCH + CUD patients.

Acute cannabis use causes increased psychotomimetic experiences in individuals prone to psychosis

BACKGROUND

Epidemiological evidence suggests a link between cannabis use and psychosis. A variety of factors have been proposed to mediate an individual's vulnerability to the harmful effects of the drug, one of which is their psychosis proneness. We hypothesized that highly psychosis-prone individuals would report more marked psychotic experiences under the acute influence of cannabis.

METHOD

A group of cannabis users (n=140) completed the Psychotomimetic States Inventory (PSI) once while acutely intoxicated and again when free of cannabis. A control group (n=144) completed the PSI on two parallel test days. All participants also completed a drug history and the Schizotypal Personality Questionnaire (SPQ). Highly psychosis-prone individuals from both groups were then compared with individuals scoring low on psychosis proneness by taking those in each group scoring above and below the upper and lower quartiles using norms for the SPQ.

RESULTS

Smoking cannabis in a naturalistic setting reliably induced marked increases in psychotomimetic symptoms. Consistent with predictions, highly psychosis-prone individuals experienced enhanced psychotomimetic states following acute cannabis use.

CONCLUSIONS

These findings suggest that an individual's response to acute cannabis and their psychosis-proneness scores are related and both may be markers of vulnerability to the harmful effects of this drug.

The adverse health effects of cannabis use: what are they, and what are their implications for policy?

BACKGROUND

The adverse health effects of cannabis are a source of contention in debates about policies towards the drug.

METHODS

This paper provides a review of epidemiological evidence on the major adverse health effects of cannabis use and considers its implications for policy.

RESULTS

The evidence strongly suggests that cannabis can adversely affect some users, especially adolescents who initiate use early and young adults who become regular users. These adverse effects probably include increased risks of: motor vehicle crashes, the development of cannabis dependence, impaired respiratory function, cardiovascular disease, psychotic symptoms, and adverse outcomes of adolescent development, namely, poorer educational outcomes and an increased likelihood of using other illicit drugs.

CONCLUSIONS

Politically, evidence of adverse health effects favours the status quo in developed countries like Australia where cannabis policy has been framed by the media as a choice between two views: (1) either cannabis use is largely harmless to most users and so we should legalize, or at the very least decriminalize its use; or (2) it harms some of its users so we should continue to prohibit its use.

An evidence synthesis approach to estimating Hepatitis C Prevalence in England and Wales

In England and Wales, routine monitoring has been consistently showing an increase in mortality and morbidity due to infection with the Hepatitis C Virus (HCV). However, the magnitude of the underlying epidemic is still the subject of debate. In this paper we present estimates of the number of individuals aged 15—59 chronically infected with HCV in 2003, derived from a Bayesian synthesis of information available from multiple sources on the size of the groups at risk for HCV and the risk specific anti-HCV prevalence. Results show that the number of chronic infections is of the order of 142,000 (95% CrI: 90,000, 231,000), with the majority (85%, 95% CrI: 74%, 93%) in injecting drug users and about 80% (95% CrI: 74%, 84%) in the age group 15—44.

Modelling disease frequency measures in schizophrenia epidemiology

BACKGROUND

Recent systematic reviews have compiled estimates related to the incidence, prevalence and mortality associated with schizophrenia. The aims of this study were (a) to model various frequency measures, (b) to examine the consistency of the published versus the modelled estimates, and (c) to explore the relative change in prevalence estimates after adjustments were made to incidence, remission, and mortality estimates.

METHODS

We identified studies that provided matched incidence and prevalence estimates. We applied the DisMod software program to model incidence from observed prevalence estimates and vice versa. The accuracy of the modelled data was compared to the published data using Mann-Whitney Signed Rank tests. Finally, we conducted several 'thought experiments' to explore the impact of changing the incidence, remission, and mortality rates on prevalence estimates.

RESULTS

We identified 24 matched-pairs of incidence and prevalence estimates. The distributions of modelled versus published estimates were significantly different. In 20 pairs, DisMod calculated modelled prevalence estimates that were higher than published estimates, while modelled incidence estimates were lower than published estimates in 21 pairs. In the majority of pairs, the difference between published and modelled estimates was greater than 50%. With respect to the 'thought experiments', a 25% reduction in mortality was associated with a 5-7% increase in prevalence, while 25% reduction in incidence or remission rates resulted in 18-23% and 1.2-2.4% decrease in prevalence estimates, respectively.

CONCLUSION

The consistency between published incidence and prevalence estimates of schizophrenia is poor. Models can help interrogate these inconsistencies and provide insights into the dynamics of schizophrenia epidemiology.