Effect of continued cannabis use on medication adherence in the first two years following onset of psychosis

Cannabis Use Frequency is Associated with PrEP Cessation and Self-reported HIV Diagnosis

To achieve stated targets in the United States of Ending the HIV Epidemic by 2030, it is necessary to decrease rates of pre-exposure prophylaxis use (PrEP) cessation. In particular, it is key to assess PrEP use and cannabis use frequency given the recent wave of cannabis decriminalization across the U.S., particularly among sexual minority men and gender diverse (SMMGD) individuals. We used data from the baseline visit of a national study of Black and Hispanic/Latino SMMGD. Among participants reporting any lifetime cannabis use, we further assessed the association between frequency of cannabis use in the past 3 months and: (1) self-reported PrEP use, (2) recency of last PrEP dose, and (3) HIV status using adjusted regression models. Compared to those who never used cannabis, odds of PrEP cessation were higher among those who used it once or twice (aOR 3.27; 95% CI 1.38, 7.78), those who used it monthly (aOR 3.41; 95% CI 1.06, 11.01), and those who used it weekly or more frequently (aOR 2.34; 95% CI 1.06, 5.16). Similarly, those reporting cannabis use 1-2 times in the past 3 months (aOR 0.11; 95% CI 0.02, 0.58) and those reporting weekly or more frequent use (aOR 0.14; 95% CI 0.03, 0.68) were each more likely to report more recent PrEP cessation. These results suggest that cannabis users in general may be a population at elevated risk of HIV diagnosis although more research regarding these findings is needed with nationally representative populations.

Cannabis Use and Symptomatic Relapse in First Episode Schizophrenia: Trigger or Consequence? Data From the OPTIMISE Study

BACKGROUND AND HYPOTHESIS

This analysis examined the relationship between cannabis use, compliance with antipsychotics and risk for relapse in patients in remission following a first episode of schizophrenia, schizophreniform, or schizoaffective disorder.

STUDY DESIGN

Analyses were performed on data from a large European study on first episode of schizophrenia, schizophreniform, or schizoaffective disorder (OPTiMiSE). After 10 weeks of antipsychotic treatment, 282/446 patients (63%) met criteria for symptomatic remission; of whom 134/282 (47.5%) then completed a 1-year follow-up. Cross-lagged models and mediation models investigated the temporal relationships between cannabis use, compliance with antipsychotics, social functioning, and symptomatic worsening/relapse.

STUDY RESULTS

Compared to nonusers, cannabis use increased risk for relapse, adjusted hazard ratio (HR) = 3.03 (SE = 0.32), P < .001, even in patients who were compliant with antipsychotic medication, adjusted HR = 2.89, (SE = 0.32), P < .001. Cannabis use preceded symptomatic worsening and was followed by worsening of Positive and Negative Syndrome Scale total score at the 1-year end-point (standardized β = 0.62, SE = 0.19, P = .001) and by worsening of social functioning (coef = -0.66, P ≤ .001).

CONCLUSIONS

In patients in remission from their first episode of schizophrenia, schizophreniform, or schizoaffective disorder, cannabis use increases the rate of relapse in both compliant and noncompliant individuals. Importantly, the temporal relationship between cannabis and relapse was that cannabis use preceded later relapse, noncompliance, and decrease in social functioning, and not that patients began to relapse, then used cannabis. Further research with a precision psychiatry approach might identify those patients in particular danger of relapse when using cannabis.

An integrated substance use treatment model for young adults with first-episode psychosis: A naturalistic pilot evaluation

AIM

Approximately 50% of individuals with first-episode psychosis meet criteria for a substance use disorder and these concurrent disorders are associated with worse long-term outcomes. Psychosocial interventions, including motivational interviewing as well as cognitive and behavioural therapies, have shown some evidence for effective treatment in substance use disorders; however, there is a paucity of existing studies that have successfully examined these interventions in first-episode psychosis.

METHODS

Participants (n = 64) received the concurrent disorders intervention, which included individual support alongside participation in at least one of two groups: a 4-week Motivational Engagement group utilizing motivational interviewing (n = 59) and an 8-week Relapse Prevention Training group emphasizing skill acquisition, which some participants entered directly (n = 5) and some participants entered following completion of the Motivational Engagement group (n = 16).

RESULTS

Participants who completed the Motivational Engagement group (n = 59) demonstrated significantly increased motivation to change substance use (d = -.0.58; t = -3.02, p < .01) and significantly decreased substance use frequency (d = 0.65; t = 3.26, p < .01). For participants who completed the Relapse Prevention Training group (n = 21), substance use frequency significantly decreased (d = 0.92; t = 3.46, p < .01) and self-efficacy in one's ability to maintain substance use changes significantly increased (d = -0.85; t = -3.59, p < .01).

CONCLUSIONS

This pilot evaluation suggests that motivational interviewing and relapse prevention skills training are acceptable and feasible interventions in the treatment of substance use disorders in young adults with first-episode psychosis.

Cognitive Behavioral Therapy Program for Cannabis Use Cessation in First-Episode Psychosis Patients: A 1-Year Randomized Controlled Trial

Despite the negative influence of cannabis use on the development and prognosis of first-episode psychosis (FEP), there is little evidence on effective specific interventions for cannabis use cessation in FEP. The aim of this study was to compare the efficacy of a specific cognitive behavioral therapy (CBT) for cannabis cessation (CBT-CC) with treatment as usual (TAU) in FEP cannabis users. In this single-blind, 1-year randomized controlled trial, 65 participants were randomly assigned to CBT-CC or TAU. The primary outcome was the reduction in cannabis use severity. The CBT-CC group had a greater decrease in cannabis use severity and positive psychotic symptoms over time, and a greater improvement in functioning at post-treatment than TAU. The treatment response was also faster in the CBT-CC group, reducing cannabis use, anxiety, positive and general psychotic symptoms, and improving functioning earlier than TAU in the follow-up. Moreover, patients who stopped and/or reduced cannabis use during the follow-up, decreased psychotic symptoms and increased awareness of disease compared to those who continued using cannabis. Early intervention based on a specific CBT for cannabis cessation, may be effective in reducing cannabis use severity, in addition to improving clinical and functional outcomes of FEP cannabis users.

Mortality in people with schizophrenia: a systematic review and meta-analysis of relative risk and aggravating or attenuating factors

People with schizophrenia die 15-20 years prematurely. Understanding mortality risk and aggravating/attenuating factors is essential to reduce this gap. We conducted a systematic review and random-effects meta-analysis of prospective and retrospective, nationwide and targeted cohort studies assessing mortality risk in people with schizophrenia versus the general population or groups matched for physical comorbidities or groups with different psychiatric disorders, also assessing moderators. Primary outcome was all-cause mortality risk ratio (RR); key secondary outcomes were mortality due to suicide and natural causes. Other secondary outcomes included any other specific-cause mortality. Publication bias, subgroup and meta-regression analyses, and quality assessment (Newcastle-Ottawa Scale) were conducted. Across 135 studies spanning from 1957 to 2021 (schizophrenia: N=4,536,447; general population controls: N=1,115,600,059; other psychiatric illness controls: N=3,827,955), all-cause mortality was increased in people with schizophrenia versus any non-schizophrenia control group (RR=2.52, 95% CI: 2.38-2.68, n=79), with the largest risk in first-episode (RR=7.43, 95% CI: 4.02-13.75, n=2) and incident (i.e., earlier-phase) schizophrenia (RR=3.52, 95% CI: 3.09-4.00, n=7) versus the general population. Specific-cause mortality was highest for suicide or injury-poisoning or undetermined non-natural cause (RR=9.76-8.42), followed by pneumonia among natural causes (RR=7.00, 95% CI: 6.79-7.23), decreasing through infectious or endocrine or respiratory or urogenital or diabetes causes (RR=3 to 4), to alcohol or gastrointestinal or renal or nervous system or cardio-cerebrovascular or all natural causes (RR=2 to 3), and liver or cerebrovascular, or breast or colon or pancreas or any cancer causes (RR=1.33 to 1.96). All-cause mortality increased slightly but significantly with median study year (beta=0.0009, 95% CI: 0.001-0.02, p=0.02). Individuals with schizophrenia <40 years of age had increased all-cause and suicide-related mortality compared to those ≥40 years old, and a higher percentage of females increased suicide-related mortality risk in incident schizophrenia samples. All-cause mortality was higher in incident than prevalent schizophrenia (RR=3.52 vs. 2.86, p=0.009). Comorbid substance use disorder increased all-cause mortality (RR=1.62, 95% CI: 1.47-1.80, n=3). Antipsychotics were protective against all-cause mortality versus no antipsychotic use (RR=0.71, 95% CI: 0.59-0.84, n=11), with largest effects for second-generation long-acting injectable anti-psychotics (SGA-LAIs) (RR=0.39, 95% CI: 0.27-0.56, n=3), clozapine (RR=0.43, 95% CI: 0.34-0.55, n=3), any LAI (RR=0.47, 95% CI: 0.39-0.58, n=2), and any SGA (RR=0.53, 95% CI: 0.44-0.63, n=4). Antipsychotics were also protective against natural cause-related mortality, yet first-generation antipsychotics (FGAs) were associated with increased mortality due to suicide and natural cause in incident schizophrenia. Higher study quality and number of variables used to adjust the analyses moderated larger natural-cause mortality risk, and more recent study year moderated larger protective effects of antipsychotics. These results indicate that the excess mortality in schizophrenia is associated with several modifiable factors. Targeting comorbid substance abuse, long-term maintenance antipsychotic treatment and appropriate/earlier use of SGA-LAIs and clozapine could reduce this mortality gap.

Cannabis use and clinical outcome in people with first-episode schizophrenia spectrum disorders over 24 months of treatment

Cannabis use is associated with an unfavourable course of illness in schizophrenia, although several factors may confound this association. In this longitudinal study, we explored the influence of cannabis use on baseline symptom severity and treatment outcomes in 98 patients with first-episode schizophrenia spectrum disorders treated with a long acting injectable antipsychotic over 24 months. Using mixed models for repeated measures, we compared visit-wise changes in psychopathology, social and occupational functioning and quality of life between recent/current cannabis users (n=45) and non-users (n=53). There were no significant group by time interactions for any of our outcomes, and with the exception of poorer functionality in cannabis users at baseline, no significant differences in these domains at baseline or month 24. Also, remission rates were similar. However, more cannabis users met our operationally defined relapse criteria compared to non-users, and more frequent cannabis use over the course of treatment, as assessed by positive urine toxicology testing, predicted relapse. Our results suggest that cannabis users do not have poorer treatment response than non-users in terms of symptom reduction over the 24 months of treatment. However, dose-related risk of relapse remains with ongoing cannabis use, possibly by directly reducing the threshold for psychotic breakthrough.

Nonadherence after hospital discharge in patients with schizophrenia or schizoaffective disorder: A six-month naturalistic follow-up study

BACKGROUND

Despite a wealth of studies seeking to identify factors associated with nonadherence few consistent predictors have been determined, and several gaps still exist in the literature.

METHOD

We assessed 110 consecutively admitted patients diagnosed with schizophrenia or schizoaffective disorder according to ICD-10 criteria. Assessments were performed during hospitalization and at six-months follow-up. Evaluation included sociodemographic, clinical, psychopathologic and treatment-related variables. Prevalence of nonadherence, associated variables, reasons for nonadherence and possible subtypes were explored. Adherence was defined as the concurrence of adherence to antipsychotic treatment and adherence to outpatient follow-up, during the six-month period.

RESULTS

Nonadherence was detected in 58.2% of patients. An identifiable profile was found in nonadherent patients. After multivariate logistic regression analysis, low socio-economic level (OR = 3.68; 95% CI = 1.42-9.53), current cannabis use or abuse (OR = 2.79; 95% CI = 1.07-7.28), nonadherence as a reason for relapse and admission (OR = 5.46; 95% CI = 2.00-14.90), and greater overall severity of symptoms at six months follow-up (OR = 2.00; 95% CI = 1.02-3.95) remained independently associated with nonadherence. Believing that medication is unnecessary was the most reported reason for nonadherence. For nonadherent patients (N = 64), two distinguishable subtypes were found: intentional nonadherence (N = 32; 50%), and unintentional nonadherence (N = 32; 50%).

CONCLUSIONS

A large percentage of patients with schizophrenia or schizoaffective disorder did not adhere to their treatment in the post-discharge follow-up period. The profile identified may enable better prevention of this problem. Specific reasons for nonadherence should also be explored to provide individualized strategies.

A systematic review of longitudinal studies investigating the impact of cannabis use in patients with psychotic disorders

Introduction: Research has established a link between cannabis use and adverse psychotic outcomes in psychosis patients. However, we have yet to determine if this relationship is maintained when controlling for important confounding variables. The following systematic review aims to investigate if the association between cannabis use and psychotic outcomes is preserved when accounting for important confounders, and if discontinued use mitigates any potential negative impacts.Areas covered: The authors conducted an exhaustive search of the MEDLINE database and Google Scholar to identify articles pertaining to the systematic review. Thirty-three articles were retained for meeting the eligibility criteria.Expert opinion: The evidence confirms an overarching pattern of negative psychotic outcomes of cannabis intake in psychosis populations, even when accounting for crucial confounders. Psychosis patients should be informed with evidence-based health information regarding the effects of cannabis use. Clinicians should systematically evaluate cannabis intake patterns in psychosis patients and offer intervention services geared toward reducing problematic consumption. Researchers should record confounding factors in a more systematic manner in future longitudinal investigations while paying careful attention to the potency and dose-response effects of the ingested cannabis. Deciders will need to investigate the impact of cannabis regulations on psychosis populations.

Factors associated with dropout at 2 years post-initiation of treatment in the first episode of schizophrenia

BACKGROUND

Prevention of new episodes during the first 2 years after a first episode of schizophrenia (FES) may delay treatment refractoriness and brain morphological changes over time. However, adherence to treatment is characteristically poor in these patients.

AIM

The aim of this study was to examine clinical and sociodemographic factors associated with patient dropout in patients with FES.

SETTING

This study was set at inpatient and outpatient services at a psychiatric hospital in the Western Cape, between 2007 and 2011.

METHODS

Data were collected as part of a prospective longitudinal study, which followed up patients with FES treated with flupenthixol decanoate. We examined the relationship between treatment adherence and sociodemographic and clinical factors at baseline and at 24 months. Unadjusted and adjusted logistic regression models were used to determine adherence variables.

RESULTS

A total of 62% of patients completed the 24 months of treatment. Participants with FES and a substance use disorder (dual diagnosis) were at greater risk of dropout (p = 0.01). On univariate analysis, dual diagnosis participants who dropped out were older (p = 0.04) had completed more years of schooling (p = 0.001), older age of onset (p = 0.02) and higher baseline positive symptoms (p = 0.05). On regression analysis, non-completer substance users achieved a higher level of education (odds ratio [OR]: 3.87, confidence interval [CI]: 1.34-11.11, p = 0.01).

CONCLUSION

Substance use disorder was associated with non-adherence to follow up in a cohort of FES patients treated with flupenthixol decanoate. Interventions that take into account age, education and baseline positive symptoms may afford the opportunity to influence adherence and patient outcome.

Individualized prediction of 2-year risk of relapse as indexed by psychiatric hospitalization following psychosis onset: Model development in two first episode samples

BACKGROUND

Although most patients with psychotic disorders experience relapse, it is not possible to predict whether or when an individual patient is going to relapse. We aimed to develop a multifactorial risk prediction algorithm for predicting risk of relapse in first episode psychosis (FEP).

METHODS

Data from two prospectively collected cohorts of FEP patients (N = 1803) were used to develop three multiple logistic prediction models to predict risk of relapse (defined as hospitalization) within the first 2 years of onset of psychosis. Model 1 (M1_S1) used data obtained from clinical notes (Sample 1) while model 2 (M2_S2) applied the same set of predictors using data obtained from research interviews (Sample 2). The final model (Sample 2: M3_S2) used the same predictors plus additional detailed information on predictors. Model performance was evaluated employing measures of overall accuracy, calibration, discrimination and internal validation.

RESULTS

In both samples, the 2-year probability of psychiatric hospitalization was 37%. Of all the models, discrimination accuracy was lowest when limited information (such as socio-demographic and clinical parameters) was included in the prediction model. Model M3_S2 using additional information (descriptors of pattern of cannabis, nicotine, alcohol and other illicit drug use) obtained from research interview had the best discrimination accuracy (Harrell's C index 0.749).

CONCLUSIONS

The measures that contributed most to predicting hospitalization are readily accessible in routine clinical practice, suggesting that a risk prediction tool based on these models would be clinically practicable following validation in independent samples and permit a personalized approach to relapse prevention in psychosis.

Cannabis Use, Cannabis Use Disorder, and Comorbid Psychiatric Illness: A Narrative Review

BACKGROUND

The landscape of attitudes, legal status and patterns of use of cannabis is rapidly changing in the United States and elsewhere. Therefore, the primary aim of this narrative review is to provide a concise overview of the literature on the comorbidity of cannabis use and cannabis use disorder (CUD) with other substance use and psychiatric disorders, and to use this information to accurately guide future directions for the field.

METHODS

A literature review of PubMed was conducted for studies relating to cannabis use, CUD, and a co-occurring psychiatric disorder. To provide an overview of representative data, the literature review focused on national-level, population-based work from the National Epidemiologic Survey on Alcohol and Related Conditions (NESARC) and National Survey on Drug Use and Health (NSDUH) surveys. Considering rapidly changing cannabis laws, recent (past five-year) studies were addressed.

RESULTS

A strong body of literature shows associations between cannabis use and CUD with other drug use, psychosis, mood disorders, anxiety disorders, and personality disorders. The strongest evidence of a potential causal relationship exists between cannabis use and psychotic disorders. While some evidence shows potential directionality between cannabis use and mood and anxiety disorders, results are inconsistent. Studies have established higher rates of CUD among those with personality disorders, but little about the specifics of this relationship is understood.

CONCLUSIONS

Although the general population in the United States increasingly perceives cannabis to be a harmless substance, empirical evidence shows that cannabis use is associated both with CUD and comorbid psychiatric illness. However, there is mixed evidence regarding the role of cannabis in the etiology, course, and prognosis of a co-occurring disorder across all categories of psychiatric disorders. Future research should expand on the existing body of literature with representative, longitudinal data, in order to better understand the acute and long-term effects of cannabis on comorbid psychiatric illness.

The influence of risk factors on the onset and outcome of psychosis: What we learned from the GAP study

The GAP multidisciplinary study carried out in South London, recruited 410 first episode of psychosis patients and 370 controls; the aim was to elucidate the multiple genetic and environmental factors influencing the onset and outcome of psychosis. The study demonstrated the risk increasing effect of adversity in childhood (especially parental loss, abuse, and bullying) on onset of psychosis especially positive symptoms. Adverse life events more proximal to onset, being from an ethnic minority, and cannabis use also played important roles; indeed, one quarter of new cases of psychosis could be attributed to use of high potency cannabis. The "jumping to conclusions" bias appeared to mediate the effect of lower IQ on vulnerability to psychosis. We confirmed that environmental factors operate on the background of polygenic risk, and that genetic and environment act together to push individuals over the threshold for manifesting the clinical disorder. The study demonstrated how biological pathways involved in the stress response (HPA axis and immune system) provide important mechanisms linking social risk factors to the development of psychotic symptoms. Further evidence implicating an immune/inflammatory component to psychosis came from our finding of complement dysregulation in FEP. Patients also showed an upregulation of the antimicrobial alpha-defensins, as well as differences in expression patterns of genes involved in NF-κB signaling and Cytokine Production. Being of African origin not only increased risk of onset but also of a more difficult course of illness. The malign effect of childhood adversity predicted a poorer outcome as did continued use of high potency cannabis.

Antipsychotic treatment failure in patients with psychosis and co-morbid cannabis use: A systematic review

Whilst the effects of cannabis preceding psychosis onset are well established, an effect post-onset is less clear. Emerging evidence suggests that cannabis use is associated with increased relapse outcomes possibly because of determinants, antipsychotic treatment failure and medication adherence, that are not mutually exclusive. Due to the paucity of literature on antipsychotic treatment failure an association with cannabis remains conjectural. This review sought to summarise current evidence regarding the effect of cannabis use on antipsychotic treatment failure among users and non-users with psychosis. Ovid databases (Embase, Journals@Ovid Full Text, OvidMEDLINE® In-Process and Other Non-Indexed Citations and PsycINFO) were searched to identify relevant articles. Seven articles met eligibility criteria. Cannabis use was associated with the following deleterious outcomes increased: odds of non-remission, prescription of unique antipsychotic medications, cumulative prescription of Clozapine and poor treatment trajectories. One study reported similar life-time, but lower past-year, rates of cannabis use in those prescribed Clozapine. Another study reported differences between groups for chlorpromazine equivalent doses for long-term Olanzapine prescription. Improved methodologies are warranted due to a lack of well-designed prospective studies and heterogeneity of key variables. There remains, despite research paucity, the need to encourage early cannabis cessation and higher-quality research to inform clinical practice.

Predictors of Hospitalization of Individuals With First-Episode Psychosis: Data From a 2-Year Follow-Up of the RAISE-ETP

OBJECTIVE

Despite treatment advances in other domains, inpatient psychiatric hospitalization rates for individuals with first-episode psychosis remain high. Even with early intervention services, a third or more of individuals are hospitalized over the first 2 years of treatment. Reducing hospitalization is desirable from the individual's perspective and for public health reasons because hospitalization costs are a major component of treatment costs.

METHODS

Univariate and multivariate baseline and time-varying covariate analyses were conducted to identify predictors of hospitalization in the Recovery After an Initial Schizophrenia Episode-Early Treatment Program (RAISE-ETP) study, a 2-year cluster randomized trial for participants experiencing a first episode of psychosis who were outpatients at study entry. The trial compared an early intervention treatment model (NAVIGATE) with usual community care at 34 clinics across the United States.

RESULTS

RAISE-ETP enrolled 404 participants of whom 382 had one or more postbaseline assessments that included hospitalization data. Thirty-four percent of NAVIGATE and 37% of usual-care participants were hospitalized during the trial. Risk analyses revealed significant predictors of hospitalization to be the number of hospitalizations before study entry; duration of untreated psychosis; and time-varying days of substance misuse, presence of positive symptoms, and beliefs about the value of medication.

CONCLUSIONS

These results indicate that hospital use may be decreased by reducing the duration of untreated psychosis and prior hospitalizations, minimizing residual symptoms, preventing substance misuse, and facilitating adherence to medication taking. Addressing these factors could enhance the impact of first-episode early intervention treatment models and also enhance outcomes of people with first-episode psychosis treated using other models.

Cannabidiol as a potential treatment for psychosis

Psychotic disorders such as schizophrenia are heterogeneous and often debilitating conditions that contribute substantially to the global burden of disease. The introduction of dopamine D2 receptor antagonists in the 1950s revolutionised the treatment of psychotic disorders and they remain the mainstay of our treatment arsenal for psychosis. However, traditional antipsychotics are associated with a number of side effects and a significant proportion of patients do not achieve an adequate remission of symptoms. There is therefore a need for novel interventions, particularly those with a non-D2 antagonist mechanism of action. Cannabidiol (CBD), a non-intoxicating constituent of the cannabis plant, has emerged as a potential novel class of antipsychotic with a unique mechanism of action. In this review, we set out the prospects of CBD as a potential novel treatment for psychotic disorders. We first review the evidence from the perspective of preclinical work and human experimental and neuroimaging studies. We then synthesise the current evidence regarding the clinical efficacy of CBD in terms of positive, negative and cognitive symptoms, safety and tolerability, and potential mechanisms by which CBD may have antipsychotic effects.

Longitudinal assessment of the effect of cannabis use on hospital readmission rates in early psychosis: A 6-year follow-up in an inpatient cohort

Cannabis is the most commonly used illicit drug in psychosis patients and has been identified as a risk factor for relapse and subsequent hospital readmission, having substantial economic implications. To clarify the contribution of cannabis consumption to hospital readmission, a consecutive inpatient cohort of 161 early psychosis patients was included into the study. Data on cannabis use at admission and number of hospital readmissions and length of stay (LOS, number of inpatient days) in a 6-year follow-up was extracted from clinical notes. 62.4% of the patients had lifetime cannabis use. Their admission lasted on average 54.3 ± 75 days and over the following 6 years patients had 2.2 ± 2.8 hospital readmissions, for a total of 197.4 ± 331.5 days. Cannabis use significantly predicted the number of hospital readmissions and LOS in the following 6 years, the latter remaining significant after adjusting for use of other substance. Cannabis-using patients of male gender and Black ethnicity had a longer LOS at follow-up compared to female patients and other ethnic groups, respectively. Having a history of cannabis use when admitted to an early intervention inpatient unit for psychosis is associated with a higher number of subsequent hospital readmissions and a longer LOS, especially in male and Black patients.

Marijuana and Psychosis: Policy Implications for Treatment Providers

In 2017, the annual prevalence of marijuana use rose to 24% among 8^th to 12^th graders, despite decreases in rates of other illicit substance use.¹ This is of concern, as increasing use is coupled with declining perception of harm among adolescents,¹ increasing potency of cannabis,² ease of adolescents' access to marijuana,¹ and progressive medicalization and legalization of marijuana. Exposure to high levels of Δ-9-tetrahydrocannabinol through cannabis use triggers repeated activation of the endogenous mesolimbic dopaminergic system, desensitization, and progressive enhancement of acquired susceptibility to psychosis.³.

Are cannabis-using and non-using patients different groups? Towards understanding the neurobiology of cannabis use in psychotic disorders

A substantial body of credible evidence has accumulated that suggest that cannabis use is an important potentially preventable risk factor for the development of psychotic illness and its worse prognosis following the onset of psychosis. Here we summarize the relevant evidence to argue that the time has come to investigate the neurobiological effects of cannabis in patients with psychotic disorders. In the first section we summarize evidence from longitudinal studies that controlled for a range of potential confounders of the association of cannabis use with increased risk of developing psychotic disorders, increased risk of hospitalization, frequent and longer hospital stays, and failure of treatment with medications for psychosis in those with established illness. Although some evidence has emerged that cannabis-using and non-using patients with psychotic disorders may have distinct patterns of neurocognitive and neurodevelopmental impairments, the biological underpinnings of the effects of cannabis remain to be fully elucidated. In the second and third sections we undertake a systematic review of 70 studies, including over 3000 patients with psychotic disorders or at increased risk of psychotic disorder, in order to delineate potential neurobiological and neurochemical mechanisms that may underlie the effects of cannabis in psychotic disorders and suggest avenues for future research.