Cannabis and cognitive functions: a prospective study

Exploring the interplay between addiction and time perception: A systematic review and meta-analysis

Prior studies have investigated the immediate impacts of substances on temporal perception, the impact of temporal outlook, and the consequences of modified temporal perception on addictive behaviors. These inquiries have provided valuable perspectives on the intricate associations between addiction and time perception, enriching the groundwork for forthcoming research and therapeutic strategies. This comprehensive review aims to further explore intricate correlation among diverse addictive substances-namely alcohol, cannabis, nicotine, opioids-and non-substance addictions such as internet gaming, elucidating their influence on temporal perception. Adhering to the PICOS method and adhering to PRISMA guidelines, we systematically reviewed and critically evaluated all existing research concerning temporal perception in individuals with substance and non-substance use disorders. Specifically, our analyses involved 31 pertinent articles encompassing six unique groups-alcohol, nicotine, cannabis, stimulants, opioids, and internet-related addictions-sourced from a pool of 551 papers. The findings revealed differences in time perception between addicts and control groups, as indicated by medium to large effect sizes (Hedge's g = 0.8, p < 0.001). However, the nature of these differences-whether they predominantly involve time overestimation or underestimation-is not yet definitively clear. This variability underscores the complexity of the relationship between addiction and temporal perception, paving the way for further research to unravel these intricate dynamics.

Pupillary effects in habitual cannabis consumers quantified with pupillography

Driving under the influence of alcohol (DUIA) and drugs (DUID) is considered an elevated risk for traffic safety. When assessing a driver's fitness to drive, standardized and objective measurement methods are still required, in order to clarify the question whether an individual is under the influence of substances acting on the central nervous system (CNS). We exposed healthy test subjects (n=41) as well as persons who were under the influence of cannabis after repeated inhalation to multiple light stimuli using infrared technology and measured the pupillary light reflex (PLR). Toxicological tests of blood samples taken from every subject followed. The aims of this study were to assess the differences in pupillography response between cannabis consumers after a washout period and no cannabis consumers as well as the dose related effects on pupillography parameters of cannabis in cannabis consumers. All four pupillary parameters changed according to a weakened pupil function after acute administration of cannabis in all test subjects. Furthermore, it could be observed that habitual cannabis consumers showed an altered pupillary function just before the first dose was taken, suggesting that the long-term effects and addiction also have to be taken into account, when effects of the CNS are discussed. The results of the present study show that almost all pupil parameters could be reliable indicators for the detection of subjects under the acute effect of cannabis.

Multiple Sclerosis, Cannabis Use, and Clinical Disability: A Preliminary [18F]-Fluorodeoxyglucose Positron Emission Tomography Study

Introduction: Long-term consequences of medicinal cannabis use in people with multiple sclerosis (PwMS) are unknown. This study investigated whether PwMS using cannabis had lower resting brain glucose uptake (GU) and worse clinical test results compared with nonusers. Methods: Sixteen PwMS, eight users, underwent clinical testing followed by [¹⁸F]-Fluorodeoxyglucose positron emission tomography/computed tomography imaging. Results: Users had lower cognitive function test scores, but performed similarly on the other clinical evaluations. Accounting for disease duration, resting brain GU was similar between the groups. Conclusions: Lower cognitive function was not associated with resting brain GU. Cognitive dysfunction may be a contraindication or consequence of cannabis use in PwMS.

A review of Indian research on co-occurring cannabis use disorders& psychiatric disorders

BACKGROUND & OBJECTIVES

Cannabis is a widely used illicit drug and its use is often associated with co-occurring psychiatric disorders. This systematic review was aimed to provide information on the published Indian studies on co-occurring cannabis use disorders and psychiatric disorders.

METHODS

An electronic search of available Indian literature using relevant search terms was carried out in May 2015 and 52 articles in English language published from India were included in the current review.

RESULTS

Studies on cannabis and associated psychotic disorders (n=16) chiefly described acute episodes with predominant positive symptoms, following cannabis use. Some studies (n=6) observed an overall increased prevalence of all psychiatric disorders and symptoms owing to cannabis use, while others (n=14) elaborated on high rates of substance use in those with psychiatric disorders. The effect of cannabis use on cognitive function was the focus of some of the Indian studies (n=7). All these studies barring one had all male subjects, and a single study described the service delivery model for those with dual diagnosis disorders in India. Most of the research used cross-sectional observational design and focussed on treatment-seeking population.

INTERPRETATION & CONCLUSIONS

A review of Indian literature on cannabis use and its association with psychiatric disorders indicates a high co-prevalence of psychotic disorders, especially in vulnerable individuals as well as high rates of co-occurrence of other psychiatric comorbidities. However, there is limited focus on exploring the aetiological association between cannabis use and psychiatric disorders; understanding the neurobiology of this association and management-related issues.

Association of Cannabis With Cognitive Functioning in Adolescents and Young Adults: A Systematic Review and Meta-analysis

IMPORTANCE

Substantial shifts in perception and policy regarding cannabis have recently occurred, with use of cannabis increasing while its perceived harm decreases. One possible risk of increased cannabis use is poorer cognitive functioning, especially in youth.

OBJECTIVE

To provide the first quantitative synthesis of the literature examining cannabis and cognitive functioning in adolescents and young adults (with a mean age of 26 years and younger).

DATA SOURCES

PubMed, PsycInfo, Academic Search Premier, Scopus, and bibliographies of relevant reviews were searched for peer-reviewed, English-language studies from the date the databases began through May 2017.

STUDY SELECTION

Consensus criteria were used to determine study inclusion through abstract and manuscript review.

DATA EXTRACTION AND SYNTHESIS

This study followed Meta-analysis of Observational Studies in Epidemiology guidelines. Effect size estimates were calculated using multivariate mixed-effects models for cognitive functioning outcomes classified into 10 domains.

MAIN OUTCOMES AND MEASURES

Results from neurocognitive tests administered in cross-sectional studies were primary outcomes, and we examined the influence of a priori explanatory variables on variability in effect size.

RESULTS

Sixty-nine studies of 2152 cannabis users (mean [SD] age, 20.6 [2.8] years; 1472 [68.4%] male) and 6575 comparison participants with minimal cannabis exposure were included (mean [SD] age, 20.8 [3.4]; 3669 [55.8%] male). Results indicated a small overall effect size (presented as mean d) for reduced cognitive functioning associated with frequent or heavy cannabis use (d, -0.25; 95% CI, -0.32 to -0.17; P < .001). The magnitude of effect sizes did not vary by sample age or age at cannabis use onset. However, studies requiring an abstinence period longer than 72 hours (15 studies; n = 928) had an overall effect size (d, -0.08; 95% CI, -0.22 to 0.07) that was not significantly different from 0 and smaller than studies with less stringent abstinence criteria (54 studies; n = 7799; d, -0.30; 95% CI, -0.37 to -0.22; P = .01).

CONCLUSIONS AND RELEVANCE

Associations between cannabis use and cognitive functioning in cross-sectional studies of adolescents and young adults are small and may be of questionable clinical importance for most individuals. Furthermore, abstinence of longer than 72 hours diminishes cognitive deficits associated with cannabis use. Although other outcomes (eg, psychosis) were not examined in the included studies, results indicate that previous studies of cannabis in youth may have overstated the magnitude and persistence of cognitive deficits associated with use. Reported deficits may reflect residual effects from acute use or withdrawal. Future studies should examine individual differences in susceptibility to cannabis-associated cognitive dysfunction.

Adolescent cannabis use and brain systems supporting adult working memory encoding, maintenance, and retrieval

Given prior reports of adverse effects of cannabis use on working memory, an executive function with a protracted developmental course during adolescence, we examined associations between developmental patterns of cannabis use and adult working memory (WM) processes. Seventy-five adults with longitudinal assessments of cannabis use (60 with reported use, 15 with no reported use) and prenatal drug exposure assessment completed a spatial WM task during fMRI at age 28. All subjects passed a multi-drug urine screen on the day of testing and denied recreational drug use in the past week. A fast event-related design with partial trials was used to separate the BOLD response associated with encoding, maintenance, and retrieval periods of the WM task. Behavioral results showed that subjects who began using cannabis earlier in adolescence had longer reaction times (RT) than those with later initiation. Cannabis age of onset was further associated with reduced posterior parietal cortex (PPC) encoding BOLD activation, which significantly mediated age of onset WM RT associations. However, cannabis age of onset brain-behavior associations did not differ between groups with a single reported use and those with repeated use, suggesting age of onset effects may reflect substance use risk characteristics rather than a developmentally-timed cannabis exposure effect. Within repeated cannabis users, greater levels of total cannabis use were associated with performance-related increases in dorsolateral prefrontal cortex (DLPFC) activation during maintenance. This pattern of significant results remained unchanged with inclusion of demographic and prenatal measures as covariates. Surprisingly, however, at the group level, cannabis users generally performed better than participants who reported never using cannabis (faster RT, higher accuracy). We extend previous investigations by identifying that WM associations with cannabis age of onset may be primary to PPC stimulus encoding activity, while the amount of cannabis use is associated with DLPFC maintenance processes. Poorer performance of participants who reported never using cannabis and the consistency of cannabis age of onset associations across single and repeated users limit interpretation of direct developmental effects of cannabis on WM in adulthood.

The relationship between bipolar disorder and cannabis use in daily life: an experience sampling study

Objectives

Although cannabis use is common in bipolar disorder and may contribute to worse clinical outcomes, little is understood about the relationship between this drug and bipolar disorder over the course of daily life. The aim of study was to examine the effect of cannabis on affect and bipolar symptoms in a group of individuals with bipolar disorder.

Methods

Twenty-four participants with bipolar disorder type I or type II completed diaries for 6 days using Experience Sampling Methodology to investigate the temporal associations between cannabis, affect and bipolar disorder symptoms.

Results

The results indicated that higher levels of positive affect increase the odds of using cannabis (OR:1.25 ,CI:1.06–1.47, P=0.008). However, neither negative affect, manic nor depressive symptoms predicted the use of cannabis. Cannabis use was associated with subsequent increases in positive affect (β=0.35, CI:0.20-0.51, P=0.000), manic symptoms (β=0.20,CI:0.05-0.34, P=0.009) and depressive symptoms (β= 0.17,CI:0.04-0.29, P=0.008).

Conclusion

The findings indicate that cannabis use is associated with a number of subsequent psychological effects. However there was no evidence that individuals with BD were using cannabis to self-medicate minor fluctuations in negative affect or bipolar disorder symptoms over the course of daily life. The findings in relation to existing literature and clinical implications are discussed.

Medial temporal structures and memory functions in adolescents with heavy cannabis use

Converging lines of evidence suggest an adverse effect of heavy cannabis use on adolescent brain development, particularly on the hippocampus. In this preliminary study, we compared hippocampal morphology in 14 "treatment-seeking" adolescents (aged 18-20) with a history of prior heavy cannabis use (5.8 joints/day) after an average of 6.7 months of drug abstinence, and 14 demographically matched normal controls. Participants underwent a high-resolution 3D MRI as well as cognitive testing including the California Verbal Learning Test (CVLT). Heavy-cannabis users showed significantly smaller volumes of the right (p < 0.04) and left (p < 0.02) hippocampus, but no significant differences in the amygdala region compared to controls. In controls, larger hippocampus volumes were observed to be significantly correlated with higher CVLT verbal learning and memory scores, but these relationships were not observed in cannabis users. In cannabis users, a smaller right hippocampus volume was correlated with a higher amount of cannabis use (r = -0.57, p < 0.03). These data support a hypothesis that heavy cannabis use may have an adverse effect on hippocampus development. These findings, after an average 6.7 month of supervised abstinence, lend support to a theory that cannabis use may impart long-term structural and functional damage. Alternatively, the observed hippocampal volumetric abnormalities may represent a risk factor for cannabis dependence. These data have potential significance for understanding the observed relationship between early cannabis exposure during adolescence and subsequent development of adult psychopathology reported in the literature for schizophrenia and related psychotic disorders.

The influence of recency of use on fMRI response during spatial working memory in adolescent marijuana users

Some neurocognitive recovery occurs within a month of abstinence from heavy marijuana use, yet functional magnetic resonance imaging (fMRI) has revealed altered activation among recent and abstinent adult users. We compared fMRI response during a spatial working memory (SWM) task between adolescent marijuana users with brief and sustained durations of abstinence. Participants were 13 recent users (two to seven days abstinent), 13 abstinent users (27 to 60 days abstinent), and 18 nonusing controls, all ages 15 to 18. Groups were similar on demographics, had no psychiatric or medical disorders, and user groups were similar on substance histories. Teens performed a two-back SWM task during fMRI. Recent users showed greater fMRI response in medial and left superior prefrontal cortices, as well as bilateral insula. Abstinent users had increased response in the right precentral gyrus (clusters > or = 1328 microl, p < .05). Results suggest that adolescents who recently used marijuana show increased brain activity in regions associated with working memory updating and inhibition. This study preliminarily suggests that (1) recent marijuana use may disrupt neural connections associated with SWM and result in compensatory brain response, and (2) sustained abstinence from marijuana may be associated with improvements in SWM response among adolescents.

Longitudinal study of cognition among adolescent marijuana users over three weeks of abstinence

BACKGROUND

Cognitive deficits that persist up to a month have been detected among adult marijuana users, but decrements and their pattern of recovery are less known in adolescent users. Previously, we reported cognitive deficits among adolescent marijuana users after one month of abstinence (Medina, Hanson, Schweinsburg, Cohen-Zion, Nagel, & Tapert, 2007). In this longitudinal study, we characterized neurocognitive changes among marijuana-using adolescents across the first three weeks of abstinence.

METHOD

Participants were adolescent marijuana users with limited alcohol and other drug use (n=19) and demographically similar non-using controls (n=21) ages 15-19. Participants completed a brief neuropsychological battery on three occasions, after 3days, 2weeks, and 3weeks of stopping substance use. Abstinence was ascertained by decreasing tetrahydrocannabinol metabolite values on serial urine drug screens. Verbal learning, verbal working memory, attention and vigilance, and time estimation were evaluated.

RESULTS

Marijuana users demonstrated poorer verbal learning (p<.01), verbal working memory (p<.05), and attention accuracy (p<.01) compared to controls. Improvements in users were seen on word list learning after 2weeks of abstinence and on verbal working memory after 3weeks. While attention processing speed was similar between groups, attention accuracy remained deficient in users throughout the 3-week abstinence period.

CONCLUSIONS

This preliminary study detected poorer verbal learning and verbal working memory among adolescent marijuana users that improved during three weeks of abstinence, while attention deficits persisted. These results implicate possible hippocampal, subcortical, and prefrontal cortex abnormalities.

Abnormal cerebellar morphometry in abstinent adolescent marijuana users

Functional neuroimaging data from adults have, in general, revealed frontocerebellar dysfunction associated with acute and chronic marijuana (MJ) use. The goal of this study was to characterize cerebellar volume in adolescent chronic MJ users following 1 month of monitored abstinence. Participants were MJ users (n=16) and controls (n=16) aged 16-18 years. Extensive exclusionary criteria included history of psychiatric or neurologic disorders. Drug use history, neuropsychological data, and structural brain scans were collected after 28 days of monitored abstinence. Trained research staff defined cerebellar volumes (including three cerebellar vermis lobes and both cerebellar hemispheres) on high-resolution T1-weighted magnetic resonance images. Adolescent MJ users demonstrated significantly larger inferior posterior (lobules VIII-X) vermis volume than controls, above and beyond effects of lifetime alcohol and other drug use, gender, and intracranial volume. Larger vermis volumes were associated with poorer executive functioning. Following 1 month of abstinence, adolescent MJ users had significantly larger posterior cerebellar vermis volumes than non-using controls. These greater volumes are suggested to be pathological based on linkage to poorer executive functioning. Longitudinal studies are needed to examine typical cerebellar development during adolescence and the influence of marijuana use.

The human toxicity of marijuana: a critique of a review by Nahas and Latour

A review entitled "The human toxicity of marijuana" was published in 1992 in the Medical Journal of Australia. The authors claimed that the adverse effects of cannabis use have been trivialized and that the effects are much more serious than earlier reported. We have made a careful study of this review and examined the claims made. We compared the claims of the authors with the information contained in the documents they cited and found that at least 28 of the 35 citations in this article were cited inaccurately. Five of these publications were misquoted, or the findings of the study were not fully reported. Twenty-three citations contained other errors, leaving only six to eight (two citations could not be retrieved because of their obscurity) accurate citations among 35. All of these inaccuracies operate in the direction of finding an adverse effect of marijuana.

Real-world memory and executive processes in cannabis users and non-users

The relationships between executive processes, associative learning and different aspects of real world memory functioning were explored in a sample of cannabis users and nonusers. Measures of executive component processes, associative learning, everyday memory, prospective memory, and cognitive failures were administered. Relative to nonusers, cannabis users were found to be impaired in several aspects of real world memory functioning. No other group differences were apparent. The absence of cannabis related deficits in those executive component processes and aspects of learning that are believed to support real world memory processes is surprising given that cannabis related deficits were obtained in real world memory. The present results are discussed within the context of neuroimaging evidence which suggests that cannabis users may exhibit different patterns of neural activation when performing executive tasks while not always exhibiting deficits on these tasks.

Abstinent adolescent marijuana users show altered fMRI response during spatial working memory

Marijuana is the most widely used illicit substance among teenagers, yet little is known about the possible neural influence of heavy marijuana use during adolescence. We previously demonstrated an altered functional magnetic resonance imaging (fMRI) activity related to spatial working memory (SWM) among adolescents who were heavy users of after an average of 8 days of abstinence, but the persisting neural effects remain unclear. To characterize the potentially persisting neurocognitive effects of heavy marijuana use in adolescence, we examined fMRI response during SWM among abstinent marijuana-using teens. Participants were 15 MJ teens and 17 demographically similar non-using controls, ages 16-18. Teens underwent biweekly urine toxicology screens to ensure abstinence for 28 days before fMRI acquisition. Groups performed similarly on the SWM task, but MJ teens demonstrated lower activity in right dorsolateral prefrontal and occipital cortices, yet significantly more activation in right posterior parietal cortex. MJ teens showed abnormalities in brain response during a SWM task compared with controls, even after 1 month of abstinence. The activation pattern among MJ teens may reflect different patterns of utilization of spatial rehearsal and attention strategies, and could indicate altered neurodevelopment or persisting abnormalities associated with heavy marijuana use in adolescence.

Neuropsychological functioning in adolescent marijuana users: subtle deficits detectable after a month of abstinence

In adults, studies examining the long-lasting cognitive effects of marijuana use demonstrate subtle deficits in attention, executive function, and memory. Because neuromaturation continues through adolescence, these results cannot necessarily generalize to adolescent marijuana users. The goal of this study was to examine neuropsychological functioning in abstinent marijuana using and demographically similar control adolescents. Data were collected from 65 adolescent marijuana users (n=31, 26% females) and controls (n=34, 26% females) 16-18 years of age. Extensive exclusionary criteria included independent psychiatric, medical, and neurologic disorders. Neuropsychological assessments were conducted after>23 days of monitored abstinence. After controlling for lifetime alcohol use and depressive symptoms, adolescent marijuana users demonstrated slower psychomotor speed (p<.05), and poorer complex attention (p<.04), story memory (p<.04), and planning and sequencing ability (p<.001) compared with controls. Post hoc analysis revealed that the number of lifetime marijuana use episodes was associated with poorer cognitive function, even after controlling for lifetime alcohol use. The general pattern of results suggested that, even after a month of monitored abstinence, adolescent marijuana users demonstrate subtle neuropsychological deficits compared with nonusers. It is possible that frequent marijuana use during adolescence may negatively influence neuromaturation and cognitive development.

Self-change: A pathway to cannabis abuse resolution

Long-term daily cannabis abusers (N = 25) who without treatment stopped using cannabis for at least one year were interviewed about their past substance use, antecedents to change, and factors supportive of change. Respondents' cannabis problems decreased in the year prior to their recovery compared to their lifetime use. Respondents described their successful quit attempts through structured interviews and autobiographical narratives. The narratives were content analyzed for factors related to recovery. The reports indicated that marijuana cessation was motivated more by internal than external factors, and the most common precipitants of quit attempts were cognitive anti-cannabis factors. The major reason reported by respondents for stopping cannabis was a change in how they viewed their cannabis use, followed by negative personal effects. The most common reported maintenance factors were avoidance of situations in which cannabis was used, changes in lifestyle, and the development of non-cannabis-related interests. Cognitive and respiratory functioning were also assessed. Lastly, more than 75% of respondents reported not seeking treatment because they believed it was not needed or because they wanted to quit on their own. Directions for future research are offered.

Imaging of the brain cannabinoid system

This review covers two major strategies for imaging of the brain cannabinoid system: autoradiography and in vivo neuroimaging. Cannabinoid receptors can be imaged directly with autoradiography in brain slices using radiolabeled cannabinoid receptor ligands. In addition, the effects of pharmacologic doses of unlabeled cannabinoid drugs can be autoradiographically imaged using indicators of blood flow or indicators of metabolism such as glucose analogs. Although cannabinoid imaging is a relatively new topic of research compared to imaging of other drugs of abuse, autoradiographic strategies have produced high-quality information about the distribution of brain cannabinoid receptors and the effects of cannabinoid drugs on brain metabolism. In vivo neuroimaging, in contrast to autoradiography, utilizes noninvasive techniques such as positron emission tomography (PET), single photon emission computed tomography (SPECT), and magnetic resonance imaging (MRI) to image both the binding and the effects of drugs within living brain. These techniques are well developed; however, in vivo imaging of cannabinoid systems is in a very preliminary state. Early results have been promising yet hard to generalize. Definitive answers to some of the most important questions about cannabinoid drugs and their effects await development of suitable in vivo neuroimaging ligands for cannabinoid systems.

Performance of heavy marijuana-smoking adolescents on a laboratory measure of motivation

Marijuana smoking produces effects that may persist for hours or days beyond the period of acute intoxication. Despite evidence that adolescence represents a period of heightened exposure to marijuana, little research exists regarding possible impairment in adolescents who smoke marijuana regularly, and none exists regarding basic behavioral processes. In the present study, adolescents who smoked marijuana on a regular basis (near daily) were compared to a control group of adolescents on a two-option experimental task designed to measure motivation. The contingencies were arranged such that one option (work), which required systematically increasing response output, initially produced greater rates of monetary reinforcement than an alternative option (non-work) that required no response output to earn money. Switching to the non-work option was interpreted as a measure of reduced motivation. Significant differences were found between the groups: the marijuana-smoking participants switched earlier to the non-work option, and derived a greater percentage of their earnings from the non-work option. These differences existed when controlling for differences in cognitive aptitude, gender, and the presence of conduct disorder. A significant correlation between cannabinoid levels and percent of earnings derived from the non-work option suggests that these effects could be associated with the presence of cannabinoids in the marijuana-smoking group.

A peek into Pandora's box: the medical excuse marijuana controversy

The smoking of marijuana for medicinal applications is a volatile and difficult issue for the medical and regulatory communities which has reached the forefront of discussions of public policy. Any consideration of this issue must take into account the substantial toxicity, impurity, and morbidity associated with marijuana use. Several states have passed ballot initiatives or legislation that allow a medical excuse for possession of marijuana. These initiatives bypass the Food and Drug Administration process of proving safety and efficacy, and they have created serious regulatory dilemmas for state regulatory boards. Several examinations of the issue have consistently drawn question to the validity of smoking an impure substance while voicing concern for the well being of patients in need. The historical, social, medical, and legal issues are examined.

Visual search in long-term cannabis users with early age of onset

The present research tested the hypothesis that there is a specific deficit in visual scanning in chronic users of cannabis with early onset of their drug consumption (age 14 to 16). 17 users and 20 control participants were asked to search for targets on a 5 x 5 stimulus array while their eye movements were monitored. Cannabis users showed less effective search behavior, including longer response times and more fixations at about the same error level. Search patterns were more conservative and included more frequent reinspections of previously fixated areas. In sum, the results point to two loci of adverse effects: an impairment in visual short-term memory, and less effective visual processing at a more strategic, top down controlled level.

Nonacute (residual) neuropsychological effects of cannabis use: a qualitative analysis and systematic review

Because there is a possibility that cannabis or cannabis-like molecules might be used as treatments for certain conditions in the future, it becomes important to consider the possible adverse effects of these compounds. In this paper, the authors review the evidence for persisting effects of nonacute cannabis use on the central nervous system, as reflected by alteration in neuropsychological performance. From the 40 articles that met criteria for inclusion in this review, the authors could not detect consistent evidence for persisting neuropsychological deficits in cannabis users; however, 22 of the 40 studies reported at least some subtle impairments. The inability to reach a firm conclusion results largely from methodological limitations inherent in most studies. These are considered in detail to inform future studies on (nonacute) consequences of cannabis consumption on cognitive abilities.

Marijuana and Job Performance: Comparing the Major Streams of Research

Though some estimate that marijuana use has cost U.S. companies billions of dollars in lost productivity, the relationship between use of marijuana and job performance is far from clear. In this paper, I review studies on this topic from four different methodological perspectives and discuss models to account for their apparently contradictory findings. This discussion suggests hypotheses for future research addressing possible reasons for inconsistencies in past findings.

Marijuana use prevention: the In-DEPTH model program

Over the past five years marijuana use has doubled among eighth, 10th and 12th grade students, and in several demographics it has tripled. The recent debate over the legalization of medical marijuana (California's Proposition 215), positive media messages, lack of parent/child discussion, and denial by schools and communities may be contributing factors to the rise of drug use among adolescents. The In-DEPTH program, a unique drug education model that educates, prevents, and provides intervention strategies in adolescent marijuana use, has in small multisite surveys shown initial success in decreasing marijuana use and positively changing beliefs. The program is based on pharmacology, addiction medicine principles, economics and the pharmaceutical sales model, and examines drug dealing as well as drug use.

Marijuana. Respiratory tract effects

Daily marijuana smoking has been clearly shown to have adverse effects on pulmonary function and produce respiratory symptomatology (cough, wheeze, and sputum production) similar to that of tobacco smokers. Based on the tobacco experience, decrements in pulmonary function may be predictive of the future development of chronic obstructive pulmonary disease (COPD). However, in the absence of alpha-1-antitrypsin deficiency, the habitual marijuana-only smoker would likely have to smoke 4-5 joints per day for a span of at least 30 yr in order to develop overt manifestations of COPD. The mutagenic/carcinogenic properties of marijuana smoke are also well-established. The potential for induction of laryngeal, oropharyngeal, and possibly bronchogenic carcinoma from marijuana has been documented by several case reports and observational series. Despite this, a relative risk ratio for the development of these tumors has not yet been quantified. Based on a higher frequency of case reports for upper airway cancer compared to bronchogenic carcinoma, marijuana smoking may have a more deleterious effect on the upper respiratory tract. However, this hypothesis remains speculative at best, pending confirmation by longitudinal studies.

Cannabinoid-induced alterations in regional cerebral blood flow in the rat

A specific receptor for cannabinoids has been characterized at the pharmacological, molecular, and neuroanatomical level. However, less is known of the functional localization in the brain for the behavioral and physiological actions of these drugs. We have examined the effects of delta 9-tetrahydrocannabinol (THC) and its active metabolite 11-OH-THC on regional cerebral blood flow in the rat in order to determine functional CNS sites of action for the cannabinoids. Conscious rats were injected i.v. with one of four doses of THC (0.5, 1, 4, 16 mg/kg). 11-OH-THC (4 mg/kg), or vehicle 30 min prior to sacrifice. Regional cerebral blood flow was determined autoradiographically using the freely diffusible tracer method of Sakaruda et al. Changes in regional cerebral blood flow were observed in 16 of the 37 areas measured. Decreases in regional cerebral blood flow following THC were seen in such areas as the CA1 region of the hippocampus, frontal and medial prefrontal cortex, the nucleus accumbens, and the claustrum. Thresholds for these effects ranged from 0.5 to 16 mg/kg. Areas unaffected by THC include the medial septum, ventral tegmental area, caudate, temporal, parietal and occipital cortex, and cerebellum. These data indicate that THC and its active metabolite, 11-OH-THC, cause a heterogeneous alteration in the activity of specific CNS sites, many of which are involved in the characteristic behavioral actions of THC.

Very long-term users of marijuana in the United States: a pilot study

The authors recruited a sample of 37 Americans, aged 30-74, who had smoked marijuana on at least 5,000 separate occasions. These subjects were found to span a wide range of ethnic groups, educational backgrounds, occupations, and annual income; they did not display any obvious features which distinguished them from the population as a whole. They typically began smoking in the 1960s or early 1970s, and then continued to smoke heavily into middle adulthood because they felt that marijuana relieved unpleasant feeling states such as anxiety or depression. To our knowledge, individuals of this type have not previously been examined; further studies of older, long-term American marijuana users are needed.

Brain glucose metabolism in chronic marijuana users at baseline and during marijuana intoxication

Despite the widespread abuse of marijuana, knowledge about its effects in the human brain is limited. Brain glucose metabolism with and without delta 9 tetrahydrocannabinol (THC) (main psychoactive component of marijuana) was evaluated in eight normal subjects and eight chronic marijuana abusers with positron emission tomography. At baseline, marijuana abusers showed lower relative cerebellar metabolism than normal subjects. THC increased relative cerebellar metabolism in all subjects, but only abusers showed increases in orbitofrontal cortex, prefrontal cortex, and basal ganglia. Cerebellar metabolism during THC intoxication was significantly correlated with the subjective sense of intoxication. The decreased cerebellar metabolism in marijuana abusers at baseline could account for the motor deficits previously reported in these subjects. The activation of orbitofrontal cortex and basal ganglia by THC in the abusers but not in the normal subjects could underlie one of the mechanisms leading to the drive and the compulsion to self-administer the drug observed in addicted individuals.

Effects of marijuana on performance of a computerized cognitive-neuromotor test battery

To evaluate the sensitivity of a computerized cognitive-neuromotor test battery in assessing the effects of marijuana (delta-9-tetrahydrocannabinol [THC]), we conducted a study of 10 healthy male volunteers who were experienced marijuana smokers. After extensive training on the performance tasks, each subject was tested on three separate days after smoking a cigarette containing either 1.75% THC, 3.55% THC, or placebo according to a randomized double-blind repeated measures design. Testing was carried out before smoking and 30, 90, and 150 minutes after smoking the cigarette. Of the five tasks employed, the digit-symbol substitution test with memory and the reaction time task were the measures most sensitive to effects of marijuana. We examined the usefulness of the coefficient of variation and effect size as indices of sensitivity to be used across different types of tasks.

Effects of chronic marijuana use on human cognition

Impairments of human cognition and learning following chronic marijuana use are of serious concern, but have not been clearly demonstrated. To determine whether such impairments occurred, this study compared performance of adult marijuana users and non-users (N = 144 and N = 72, respectively) matched on intellectual functioning before the onset of drug use, i.e., on scores from standardized tests administered during the fourth grade of grammar school (Iowa Tests of Basic Skills). Subjects were given the twelfth grade versions of these tests (Iowa Tests of Educational Development) and other, computerized cognitive tests in successive test sessions. "Heavy" marijuana use (defined by use seven or more times weekly) was associated with deficits in mathematical skills and verbal expression in the Iowa Tests of Educational Development and selective impairments in memory retrieval processes in Buschke's Test. The retrieval impairments were restricted to words that were easy to visualize. Impairments depended on the frequency of chronic marijuana use, i.e., "light" and "intermediate" marijuana use (defined by use one to four and five to six times weekly, respectively) were not associated with deficits. Intermediate use was associated with superior performance in one condition ("fuzzy" concepts) of a Concept Formation test.