Research
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CASA: National Center on Addiction and Substance Abuse at Columbia University. (2001, September). Malignant Neglect: Substance Abuse and America's Schools.
Drug Enforcement Administration. (2010). Speaking Out Against Drug Legalization. Washington, DC: Drug Enforcement Administration.
NEW! Brett, M. (2012, May). Cannabis: A General Survey of its Harmful Effects. Report submitted to The Social Justice Policy Group, 2006.
Mary Brett has provided Prevent Teen Drug Use with a comprehensive report on the extensive research related to marijuana, including its effects on the cardiovascular system, immune system, reproductive system, mental health and illness, cognitive function, personality, education, and other drug use, among other topics. Mary Brett is a former Vice President of Europe Against Drugs (Erad) and is a founding member and trustee of Cannabis Skunk Sense (CanSS). She is also a member of Prisons and Addictions Forum (PandA) Center for Policy Studies and a member of World Federation Against Drugs.
Gruber, S.A., Sagar, K.A., Dahlgren, M.K., Racine, M,. & Lukas, S.E. (2011). Age of onset of marijuana use and executive function. Psychology of Addictive Behaviors. [Epub ahead of print]
Abstract: Marijuana (MJ) remains the most widely abused illicit substance in the United States, and in recent years, a decline in perceived risk of MJ use has been accompanied by a simultaneous increase in rates of use among adolescents. In this study, the authors hypothesized that chronic MJ smokers would perform cognitive tasks, specifically those that require executive function, more poorly than control subjects and that individuals who started smoking MJ regularly prior to age 16 (early onset) would have more difficulty than those who started after age 16 (late onset). Thirty-four chronic, heavy MJ smokers separated into early and late onset groups, and 28 non-MJ smoking controls completed a battery of neurocognitive measures. As hypothesized, MJ smokers performed more poorly than controls on several measures of executive function. Age of onset analyses revealed that these between-group differences were largely attributed to the early onset group, who were also shown to smoke twice as often and nearly 3 times as much MJ per week relative to the late onset smokers. Age of onset, frequency, and magnitude of MJ use were all shown to impact cognitive performance. Findings suggest that earlier MJ onset is related to poorer cognitive function and increased frequency and magnitude of MJ use relative to later MJ onset. Exposure to MJ during a period of neurodevelopmental vulnerability, such as adolescence, may result in altered brain development and enduring neuropsychological changes.
Mittleman, M. A., Lewis, R. A., Maclure, M., Sherwood, J. B., & Muller, J. E. (2000). Triggering myocardial infarction by marijuana. Circulation, 103, 2805-2809.
Abstract: Background. Marijuana use in the age group prone to coronary artery disease is higher than it was in the past. Smoking marijuana is known to have hemodynamic consequences, including a dose-dependent increase in heart rate, supine hypertension, and postural hypotension; however, whether it can trigger the onset of myocardial infarction is unknown. Methods and Results. In the Determinants of Myocardial Infarction Onset Study, we interviewed 3882 patients (1258 women) with acute myocardial infarction an average of 4 days after infarction onset. We used the case-crossover study design to compare the reported use of marijuana in the hour preceding symptoms of myocardial infarction onset to its expected frequency using self-matched control data. Of the 3882 patients, 124 (3.2%) reported smoking marijuana in the prior year, 37 within 24 hours and 9 within 1 hour of myocardial infarction symptoms. Compared with nonusers, marijuana users were more likely to be men (94% versus 67%, P,0.001), current cigarette smokers (68% versus 32%, P,0.001), and obese (43% versus 32%, P50.008). They were less likely to have a history of angina (12% versus 25%, P,0.001) or hypertension (30% versus 44%, P50.002). The risk of myocardial infarction onset was elevated 4.8 times over baseline (95% confidence interval, 2.4 to 9.5) in the 60 minutes after marijuana use. The elevated risk rapidly decreased thereafter. Conclusions. Smoking marijuana is a rare trigger of acute myocardial infarction. Understanding the mechanism through which marijuana causes infarction may provide insight into the triggering of myocardial infarction by this and other, more common stressors.
Bolla, K.I., Brown, K., Eldreth, D., Tate, K., & Cadet, J.L. (2002). Dose-related neurocognitive effects of marijuana use. Neurology, 59(9), 1337-1374
Abstract: Background. Although about 7 million people in the US population use marijuana at least weekly, there is a paucity of scientific data on persistent neurocognitive effects of marijuana use. Objective. To determine if neurocognitive deficits persist in 28-day abstinent heavy marijuana users and if these deficits are dose-related to the number of marijuana joints smoked per week. Methods. A battery of neurocognitive tests was given to 28-day abstinent heavy marijuana abusers. Results. As joints smoked per week increased, performance decreased on tests measuring memory, executive functioning, psychomotor speed, and manual dexterity. When dividing the group into light, middle, and heavy user groups, the heavy group performed significantly below the light group on 5 of 35 measures and the size of the effect ranged from 3.00 to 4.20 SD units. Duration of use had little effect on neurocognitive performance. Conclusions. Very heavy use of marijuana is associated with persistent decrements in neurocognitive performance even after 28 days of abstinence. It is unclear if these decrements will resolve with continued abstinence or become progressively worse with continued heavy marijuana use.
Kouri, E.M. (2002, February 1). Does Marijuana Withdrawal Syndrome Exist? Psychiatric Times, 19(2).
Colorado Department of Education, Dropout Prevention and Student Engagement Unit. (2011). Understand the Big Deal: How Marijuana Harms Youth.
National Institute on Drug Abuse. (2011). Marijuana: Facts Parents Need to Know. Washington, DC: National Institute on Drug Abuse.
National Institute on Drug Abuse. (2008, March). Marijuana: Facts for Teens. NIH Publication No. 08-4037.
National Institute on Drug Abuse. (2010). Marijuana Abuse. NIDA Research Report Series. US Department of Health and Human Services, National Institutes of Health.
Office of National Drug Control Policy. (2008, July). 2008 Marijuana Sourcebook; Marijuana: The Greatest Cause of Illegal Drug Abuse.
Center for Substance Abuse Research (2010, October 25). Early marijuana use related to later illicit drug abuse and dependence. CESAR Fax, 19(11).
Children's Hospital of Philadelphia (2009, February 3). Heavy Marijuana Use May Damage Developing Brain In Teens, Young Adults. ScienceDaily.
Mayet, A., Legleye, S., Falissard, B., & Chau, N. (2012). Cannabis use stages as predictor of subsequent initiation with other illicit drugs among French adolescents: Use of a multi-state model. Addictive Behaviors, 37(2), 160-166.
Abstract: The aim of this study was to confirm the influence of cannabis use patterns on the probability of initiation with other illicit drugs (OID). A French nationwide retrospective cohort on drug use was reconstituted on 29,393 teenagers. A Markov multi-state model was fitted, modelling all possible pathways from initial abstinence to cannabis initiation, daily cannabis use and OID initiation. The model was adjusted for tobacco and alcohol use. The risk for OID initiation appeared 21 times higher among cannabis experimenters and 124 times higher among daily cannabis users than among non-users. Tobacco and alcohol use were associated with a greater risk of moving on to cannabis initiation (hazard ratio (HR)=1.2 for tobacco initiation, HR=2.6 for daily tobacco use and HR=2.8 for drunkenness initiation). The results of this study provide a confirmation of a stage process in drug use, mediated by cannabis and liable to lead to OID experiment. This is compatible with the literature on the gateway theory, but goes further by modelling the entire sequence of use. OID experiment could be a consequence of initial opportunity to use the more accessible illicit drug, cannabis.
Budney, A.J., & Moore, B.A. (2002). Development and Consequences of Cannabis Dependence. Journal of Clinical Pharmacology, 42, 28S-38S.
Abstract: The past 10 to 15 years of clinical and basic research have produced strong evidence demonstrating that cannabis can and does produce dependence. Clinical and epidemiological studies indicate that cannabis dependence is a relatively common phenomenon associated with significant psychosocial impairment. Basic research has identified a neurobiological system specific to the actions of cannabinoids. Human and nonhuman studies have demonstrated a valid withdrawal syndrome that is relatively common among heavy marijuana users. Last, clinical trials evaluating treatments for cannabis dependence suggest that this disorder, like other substance dependence disorders, is responsive to intervention, yet the majority of patients have difficulty achieving and maintaining abstinence. Of concern, treatment seeking for marijuana dependence has increased almost twofold over the past 10 years. This report briefly reviews selected research literature relevant to our current understanding of cannabis dependence, its associated consequences, and treatment efficacy.
Crean RD, Crane NA, Mason BJ. (2011). An evidence-based review of acute and long-term effects of cannabis use on executive cognitive functions. Journal of Addictive Medicine, 5(1):1-8.
Abstract: Cannabis use has been shown to impair cognitive functions on a number of levels-from basic motor coordination to more complex executive function tasks, such as the ability to plan, organize, solve problems, make decisions, remember, and control emotions and behavior. These deficits differ in severity depending on the quantity, recency, age of onset and duration of marijuana use. Understanding how cannabis use impairs executive function is important. Individuals with cannabis-related impairment in executive functions have been found to have trouble learning and applying the skills required for successful recovery, putting them at increased risk for relapse to cannabis use. Here we review the research on the acute, residual, and long-term effects of cannabis use on executive functions, and discuss the implications for treatment.
Hall, W. & Solowij, N. (1998). Adverse effects of cannabis. The Lancet, 352(9140), 1611-1616.
Abstract: Cannabis is the most widely used illicit drug in many developed societies. Its health and psychological effects are not well understood and remain the subject of much debate, with opinions on its risks polarized along the lines of proponents' views on what its legal status should be. An unfortunate consequence of this polarization of opinion has been the absence of any consensus on what health information the medical profession should give to patients who are users or potential users of cannabis. There is conflicting evidence about many of the effects of cannabis use, so we summarize the evidence on the most probable adverse health and psychological consequences of acute and chronic use. This uncertainty, however, should not prevent medical practitioners from advising patients about the most likely ill-effects of their cannabis use. Here we make some suggestions about the advice doctors can give to patients who use, or are contemplating the use, of this drug.
Hii, S.W., Tam, J.D., Thompson, B.R., Naughton, M.T. (2008). Bullous lung disease due to marijuana. Respirology, 13(1), 122-127.
Abstract: Background and Objective. In contrast to the well-described effects of tobacco smoking upon pulmonary emphysema, with approximately 15% of smokers being affected at the age of 65 years, the effects of marijuana smoking are rarely reported and poorly understood. Methods. We report a series of 10 patients (mean age 41 +/- 9 years, eight male, two female), who presented over a period of 12 months to our respiratory unit with new respiratory symptoms, and who admitted to regular chronic marijuana smoking (>1 year continuously). Symptoms on presentation were dyspnoea (n = 4), pneumothorax (n = 4) and chest infection (n = 2). Results. High-resolution CT revealed asymmetrical, variably sized, emphysematous bullae in the upper and mid zones. However, the CXR was normal in four patients and lung function was normal in five. Conclusions. Marijuana smoking leads to asymmetrical bullous disease, often in the setting of normal CXR and lung function. In subjects who smoke marijuana, these pathological changes occur at a younger age (approximately 20 years earlier) than in tobacco smokers.
Jager, G., & Ramsey, N.F. (2008). Long-term consequences of adolescent cannabis exposure on the development of cognition, brain structure and function: An overview of animal and human research. Current Drug Abuse Reviews, 1(2), 114-123.
Abstract: Over the last decade there has been a steady increase in the prevalence of frequent cannabis use among teenagers, accompanied by a decrease in age of first use. Evidence from both animal and human studies suggests that the severity of the effects of cannabis use on cognitive development is dependent on the age when cannabis use begins. One possible explanation is that those who begin cannabis use early in adolescence are more likely to become heavily dependent. It is plausible that chronic cannabis abuse will then interfere with educational and vocational training. From a more biological perspective, however, use of cannabis during critical developmental periods in the still maturing brain may induce persistent alterations in brain structure and brain function. Therefore, the effects of frequent cannabis use during adolescence could be different from and more serious than during adulthood, an issue increasingly recognized in the field of cannabis research. In this paper we review the relevant animal and human literature on long-term effects of frequent exposure to cannabis during adolescence on the development of cognition, brain structure and function, and discuss implications, methodological and conceptual issues, and future prospects.
Agrawal, A., Neale, M.C., Prescott, C.A., & Kendler, K.S. (2004). A twin study of early cannabis use and subsequent use and abuse/dependence of other illicit drugs. Psychological Medicine, 34(7), 1227-1237.
Abstract: Introduction. Cannabis use is strongly associated with the use and abuse/dependence of other illicit drugs. Gateway and common liabilities models have been employed to explain this relationship. We sought to examine this association using a combination of the discordant twin design and modeling methods. Method. We assess the relationship between early cannabis use and the subsequent use and abuse/ dependence of other illicit drugs in a population-based sample of male and female twin pairs using four analyses: (i) analysis of the association between early cannabis use and other illicit drug use and abuse/dependence in the entire sample of twins, (ii) assessment of the influence of early cannabis use in twin 1 on twin 2's use or abuse/dependence of other illicit drugs, (iii) use of twin pairs discordant for early cannabis use in a discordant twin design and (iv) a model-fitting procedure. Results. We found: (i) a strong association between early cannabis use and use and abuse/dependence of other illicit drugs in the sample, (ii) twin 1's early cannabis use is significantly associated with the twin 2's other illicit drug use, (iii) the role of correlated genetic factors with some evidence for a causal influence, and (iv) the correlated liabilities model fits the data well. Conclusions. Early cannabis use is strongly associated with other illicit drug use and abuse/dependence. The relationship arises largely due to correlated genetic and environmental influences with persisting evidence for some causal influences.Fergusson, D.M., & Horwood, L.J. (2000). Does cannabis use encourage other forms of illicit drug use? Addiction, 95(4), 505-520.
Abstract: Aims. To examine the relationship between cannabis use in adolescence and the onset of other illicit drug use. Method. Data were gathered over the course of a 21-year longitudinal study of a birth cohort of 1265 New Zealand children. Measures analysed included: (a) frequency of cannabis use and other illicit drugs from 15-21; (b) family, social, educational and behavioural backgrounds of cohort members prior to 15; and (c) adolescent life-style variables. Findings. (i) By 21, nearly 70% of cohort members and used cannabis and 26% had used other illicit drugs. (ii) In all but three cases, the use of cannabis had preceded the use of illicit drugs. (iii) Those using cannabis on more than 50 occasions a year had hazards of other illicit drug use that were 140 times higher than non-users. (iv) After adjustment for covariate factors, including childhood factors, family factors and adolescent life-style factors, cannabis use remained strongly related to the onset of other forms of illicit drug use. Those using cannabis on more than 50 occasions per year had hazards of other illicit drug use that were 59.2 times higher than non-users. Conclusions. Findings support the view that cannabis may act as a gateway drug that encourages other forms of illicit drug use. None the less, the possibility remains that the association is non-causal and reflects factors that were not adequately controlled in the analysis.
Ehrenreich, H., Rinn, T., Kunert, H.J., Moeller, M.R., Poser, W., Schilling, L., Gigerenzer, G., Hoehe, M.R. (1999). Specific attentional dysfunction in adults following early start of cannabis use. Psychopharmacology, 142(3), 295-301.
Abstract: Rationale and Objective. The present study tested the hypothesis that chronic interference by cannabis with endogenous cannabinoid systems during peripubertal development causes specific and persistent brain alterations in humans. As an index of cannabinoid action, visual scanning, along with other attentional functions, was chosen. Visual scanning undergoes a major maturation process around age 12-15 years and, in addition, the visual system is known to react specifically and sensitively to cannabinoids. Methods. From 250 individuals consuming cannabis regularly, 99 healthy pure cannabis users were selected. They were free of any other past or present drug abuse, or history of neuropsychiatric disease. After an interview, physical examination, analysis of routine laboratory parameters, plasma/urine analyses for drugs, and MMPI testing, users and respective controls were subjected to a computer-assisted attention test battery comprising visual scanning, alertness, divided attention, flexibility, and working memory. Results. Of the potential predictors of test performance within the user group, including present age, age of onset of cannabis use, degree of acute intoxication (THC+THCOH plasma levels), and cumulative toxicity (estimated total life dose), an early age of onset turned out to be the only predictor, predicting impaired reaction times exclusively in visual scanning. Early-onset users (onset before age 16; n = 48) showed a significant impairment in reaction times in this function, whereas late-onset users (onset after age 16; n = 51) did not differ from controls (n = 49). Conclusions. These data suggest that beginning cannabis use during early adolescence may lead to enduring effects on specific attentional functions in adulthood. Apparently, vulnerable periods during brain development exist that are subject to persistent alterations by interfering exogenous cannabinoids.
Hall, W., & Degenhardt, L. (2009). Adverse health effects of non-medical cannabis use.
Abstract: 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.
Pope Jr., H.G., Gruber, A.J., Hudson, J.I, Cohane, G., Huestis, M.A., & Yurgelun-Todd, D. (2003). Early-onset cannabis use and cognitive deficits: What is the nature of the association? Drug and Alcohol Dependence, 69(3), 303-310.
Abstract: Background. Individuals who initiate cannabis use at an early age, when the brain is still developing, might be more vulnerable to lasting neuropsychological deficits than individuals who begin use later in life. Methods. We analyzed neuropsychological test results from 122 long-term heavy cannabis users and 87 comparison subjects with minimal cannabis exposure, all of whom had undergone a 28-day period of abstinence from cannabis, monitored by daily or every-other-day observed urine samples. We compared early-onset cannabis users with late-onset users and with controls, using linear regression controlling for age, sex, ethnicity, and attributes of family of origin. Results. The 69 early-onset users (who began smoking before age 17) differed significantly from both the 53 late-onset users (who began smoking at age 17 or later) and from the 87 controls on several measures, most notably verbal IQ (VIQ). Few differences were found between late-onset users and controls on the test battery. However, when we adjusted for VIQ, virtually all differences between early-onset users and controls on test measures ceased to be significant. Conclusions. Early-onset cannabis users exhibit poorer cognitive performance than late-onset users or control subjects, especially in VIQ, but the cause of this difference cannot be determined from our data. The difference may reflect (1). innate differences between groups in cognitive ability, antedating first cannabis use; (2). an actual neurotoxic effect of cannabis on the developing brain; or (3). poorer learning of conventional cognitive skills by young cannabis users who have eschewed academics and diverged from the mainstream culture.
Rubino, T., Realini, N., Braida, D., Guidi, S., Capurro, V., Vigano, D., � Parolaro, D. (2009). Changes in hippocampal morphology and neuroplasticity induced by adolescent THC treatment are associated with cognitive impairment in adulthood. Hippocampus, 19(8), 763-772.
Abstract: Marijuana and hashish are the illicit drugs most frequently used by human adolescents. Given the continued neurodevelopment throughout adolescence, adolescents may be more vulnerable than adults to certain neural consequences of heavy marijuana use. This study aimed to assess whether an experimental model of adolescent chronic exposure to Delta9-tetrahydrocannabinol (THC), may induce lasting effects on learning and memory. Adolescent rats have been treated with THC or its vehicle from 35 to 45 postnatal days (PND) and left undisturbed until their adulthood (75 PND) when aversive and spatial memory was assessed using the passive avoidance and radial maze tasks. No alteration was found in aversive memory, but in the radial maze THC pretreated animals exhibited a worse performance than vehicles, suggesting a deficit in spatial working memory. To correlate memory impairment to altered neuroplasticity, level of marker proteins was investigated in the hippocampus, the most relevant area mediating spatial memory. A significant decrease in the astroglial marker glial fibrillar acid protein was found as well as in pre- and postsynaptic protein expression (VAMP2, PSD95) and NMDA receptor levels in pretreated rats. To parallel these changes to alteration in dendritic morphology, Golgi-Cox staining was performed in the hippocampal dentate gyrus. Pretreated rats had a significantly lower total dendritic length and number than vehicles, as well as reduced spine density. Our data suggest that THC pretreated rats may establish less synaptic contacts and/or less efficient synaptic connections throughout the hippocampus and this could represent the molecular underpinning of the cognitive deficit induced by adolescent THC treatment.
Wilson, W., Matthew, R., Turkington, T., Hawk, T., Coleman, R.E., & Provenzale, J. (2000). Brain morphological changes and early marijuana use: A magnetic resonance and positron emission tomography study. Journal of Addictive Diseases, 19(1), 1-22.
Abstract: Background. The focus of this report is on the possible role that the age of first use of marijuana may play on brain morphology and function. Methods. Magnetic resonance imaging (MRI) and positron emission tomography (PET) were utilized to study 57 subjects. Brain volume measures (whole brain, gray matter, white matter and lateral ventricle volumes), global cerebral blood flow (CBF) and body size were evaluated. Results. There are three primary findings related to age of first use of marijuana. Subjects who started using marijuana before age 17, compared to those who started later, had smaller whole brain and percent cortical gray matter and larger percent white matter volumes. Functionally, males who started using marijuana before 17 had significantly higher CBF than other males. Both males and females who started younger were physically smaller in height and weight, with the effects being greater in males. Conclusions. These findings suggest that the age at which exposure to marijuana begins is important. Early adolescence may be a critical period for effects that are not present when exposure begins later. These results are discussed in light of reported effects of marijuana on gonadal and pituitary hormones.
Yamaguchi, K., & Kandel, D.B. (1984). Patterns of drug use from adolescence to young adulthood: III. Predictors of progression. American Journal of Public Health, 74(7), 673-681.
Abstract: Possible linkages of influence among classes of drugs in the observed sequential progression from adolescence to young adulthood are investigated through event history analyses. Three stages are examined: initiation to marijuana, to the use of other illicit drugs, and to prescribed psychoactive drugs. The data are based on a follow-up cohort of former adolescents representative of high school students in grade 10 and 11 in New York State who were reinterviewed nine years later at ages 24-25. The sequential order between alcohol and/or cigarettes and marijuana reflects not only the effect of the use of legal drugs on marijuana initiation, but also age effects on onset of these drugs, controlling for individual characteristics measured in adolescence; marijuana use by one's friends in adolescence is an additional important predictor of marijuana initiation. Prior use of marijuana is necessary for progression to other illicit drugs. Multiple factors are involved in the progression to prescribed drugs, with adolescent depressive symptomatology and use of other illicit drugs important for both sexes, and maternal use of psychoactive drugs, dropping out of school, and prior use of marijuana of additional importance for women. Although licit drugs influence initiation into marijuana independently of age effects, it is especially for the progression from marijuana to other illicit drugs that the earlier drug is associated with the progression to a higher stage drug.
Blows, S., Ivers, R.Q., Connor, J., Ameratunga, S., Woodward, M., & Norton, R. (2005). Marijuana use and car crash injury. Addiction, 100(5), 605-611.
Abstract: Aims. To investigate the relationship between marijuana use prior to driving, habitual marijuana use and car crash injury. Design and Setting. Population based case-control study in Auckland, New Zealand. Participants. Case vehicles were all cars involved in crashes in which at least one occupant was hospitalized or killed anywhere in the Auckland region, and control vehicles were a random sample of cars driving on Auckland roads. The drivers of 571 case and 588 control vehicles completed a structured interview. Measurements. Self reported marijuana use in the 3 hours prior to the crash/survey and habitual marijuana use over the previous 12 months were recorded, along with a range of other variables potentially related to crash risk. The main outcome measure was hospitalization or death of a vehicle occupant due to car crash injury. Findings. Acute marijuana use was significantly associated with car crash injury, after controlling for the confounders age, gender, ethnicity, education level, passenger carriage, driving exposure and time of day (OR 3.9, 95% CI 1.2-12.9). However, after adjustment for these confounders plus other risky driving at the time of the crash (blood alcohol concentration, seat-belt use, travelling speed and sleepiness score), the effect of acute marijuana intake was no longer significant (OR 0.8, 95% CI 0.2-3.3). There was a strong significant association between habitual use and car crash injury after adjustment for all the above confounders plus acute use prior to driving (OR 9.5, 95% CI 2.8-32.3). Conclusions. This population-based case-control study indicates that habitual use of marijuana is strongly associated with car crash injury. The nature of the relationship between marijuana use and risk-taking is unclear and needs further research. The prevalence of marijuana use in this driving population was low, and acute use was associated with habitual marijuana use, suggesting that intervention strategies may be more effective if they are targeted towards high use groups.
Ashbridge, M., Hayden, J. A., & Cartwright, J. L. (2012). Acute cannabis consumption and motor vehicle collision risk: Systematic review of observational studies and meta-analysis. British Medical Journal, 344:e536 doi: 10.1136/bmj.e536
Abstract: Objective To determine whether the acute consumption of cannabis (cannabinoids) by drivers increases the risk of a motor vehicle collision. Design. Systematic review of observational studies, with meta-analysis. Data sources. We did electronic searches in 19 databases, unrestricted by year or language of publication. We also did manual searches of reference lists, conducted a search for unpublished studies, and reviewed the personal libraries of the research team. Review methods. We included observational epidemiology studies of motor vehicle collisions with an appropriate control group, and selected studies that measured recent cannabis use in drivers by toxicological analysis of whole blood or self report. We excluded experimental or simulator studies. Two independent reviewers assessed risk of bias in each selected study, with consensus, using the Newcastle-Ottawa scale. Risk estimates were combined using random effects models. Results. We selected nine studies in the review and meta-analysis. Driving under the influence of cannabis was associated with a significantly increased risk of motor vehicle collisions compared with unimpaired driving (odds ratio 1.92 (95% confidence interval 1.35 to 2.73); P=0.0003); we noted heterogeneity among the individual study effects (I2=81). Collision risk estimates were higher in case-control studies (2.79 (1.23 to 6.33); P=0.01) and studies of fatal collisions (2.10 (1.31 to 3.36); P=0.002) than in culpability studies (1.65 (1.11 to 2.46); P=0.07) and studies of non-fatal collisions (1.74 (0.88 to 3.46); P=0.11). Conclusions. Acute cannabis consumption is associated with an increased risk of a motor vehicle crash, especially for fatal collisions. This information could be used as the basis for campaigns against drug impaired driving, developing regional or national policies to control acute drug use while driving, and raising public awareness.
Li M, Brady JE, DiMaggio CJ, Lusardi AR, Tzong KY, Li G. Marijuana use and motor vehicle crashes. Epidemiol Rev 2011 [Epub ahead of print].
Abstract: Since 1996, 16 states and the District of Columbia in the United States have enacted legislation to decriminalize marijuana for medical use. Although marijuana is the most commonly detected nonalcohol drug in drivers, its role in crash causation remains unsettled. To assess the association between marijuana use and crash risk, the authors performed a meta-analysis of 9 epidemiologic studies published in English in the past 2 decades identified through a systematic search of bibliographic databases. Estimated odds ratios relating marijuana use to crash risk reported in these studies ranged from 0.85 to 7.16. Pooled analysis based on the random-effects model yielded a summary odds ratio of 2.66 (95% confidence interval: 2.07, 3.41). Analysis of individual studies indicated that the heightened risk of crash involvement associated with marijuana use persisted after adjustment for confounding variables and that the risk of crash involvement increased in a dose-response fashion with the concentration of 11-nor-9-carboxy-delta-9-tetrahydrocannabinol detected in the urine and the frequency of self-reported marijuana use. The results of this meta-analysis suggest that marijuana use by drivers is associated with a significantly increased risk of being involved in motor vehicle crashes.
Lynch, M., Rabin, R.A., & George, T.P. (2012, January 12). The Cannabis-Psychosis Link. Psychiatric Times.
Foti, D.J., Kotov, R., Guey, L.T., Bromet, E.J. (2010). Cannabis use and the course of schizophrenia: 10-year follow up after first hospitalization. The American Journal of Psychiatry, 167(8), 987-93.
Abstract: Objective. The authors examined the relationship between cannabis use and the course of illness in schizophrenia over 10 years of follow-up after first psychiatric hospitalization. Method. The authors assessed 229 patients with a schizophrenia spectrum disorder five times: during the first admission and 6 months, 2 years, 4 years, and 10 years later. Ratings of cannabis use and psychiatric symptoms (psychotic, negative, disorganized, and depressive) were made at each assessment. Results. The lifetime rate of cannabis use was 66.2%, and survival analysis revealed that lifetime use was associated with an earlier onset of psychosis. The rates of current use ranged from 10% to 18% across assessments. Cannabis status was moderately stable, with tetrachoric correlation coefficients between waves ranging from 0.48 to 0.78. Mixed-effects logistic regression revealed that changes in cannabis use were associated with changes in psychotic symptoms over time even after gender, age, socioeconomic status, other drug use, antipsychotic medication use, and other symptoms were controlled for. Structural equation modeling indicated that the association with psychotic symptoms was bidirectional. Conclusions. Cannabis use is associated with an adverse course of psychotic symptoms in schizophrenia, and vice versa, even after taking into account other clinical, substance use, and demographic variables.
Patton, G.C., Coffey, C., Carlin, J.B., Degenhardt, L., Lynskey, M., & Hall, W. (2002). Cannabis use and mental health in young people: Cohort study. British Medical Journal, 325, 1195-1198.
Abstract: Objective. To determine whether cannabis use in adolescence predisposes to higher rates of depression and anxiety in young adulthood. Design. Seven wave cohort study over six years. Setting. 44 schools in the Australian state of Victoria. Participants. A statewide secondary school sample of 1601 students aged 14-15 followed for seven years. Main Outcome Measure. Interview measure of depression and anxiety (revised clinical interview schedule) at wave 7. Results. Some 60% of participants had used cannabis by the age of 20; 7% were daily users at that point. Daily use in young women was associated with an over fivefold increase in the odds of reporting a state of depression and anxiety after adjustment for intercurrent use of other substances (odds ratio 5.6, 95% confidence interval 2.6 to 12). Weekly or more frequent cannabis use in teenagers predicted an approximately twofold increase in risk for later depression and anxiety (1.9, 1.1 to 3.3) after adjustment for potential baseline confounders. In contrast, depression and anxiety in teenagers predicted neither later weekly nor daily cannabis use. Conclusions. Frequent cannabis use in teenage girls predicts later depression and anxiety, with daily users carrying the highest risk. Given recent increasing levels of cannabis use, measures to reduce frequent and heavy recreational use seem warranted.
Zammit, S., et al. (2002). Self-reported cannabis use as a risk factor for schizophrenia in Swedish conscripts of 1969: historical cohort study. British Medical Journal, 325, 1199-1201.
Abstract: Objective. An association between use of cannabis in adolescence and subsequent risk of schizophrenia was previously reported in a follow up of Swedish conscripts. Arguments were raised that this association may be due to use of drugs other than cannabis and that personality traits may have confounded results. We performed a further analysis of this cohort to address these uncertainties while extending the follow up period to identify additional cases. Design. Historical cohort study. Setting: 1969-70 survey of Swedish conscripts (>97% of the country's male population aged 18-20). Participants. 50 087 subjects: data were available on self reported use of cannabis and other drugs, and on several social and psychological characteristics. Main Outcome Measures. Admissions to hospital for ICD-8/9 schizophrenia and other psychoses, as determined by record linkage. Results. Cannabis was associated with an increased risk of developing schizophrenia in a dose dependent fashion both for subjects who had ever used cannabis (adjusted odds ratio for linear trend of increasing frequency 1.2, 95% confidence interval 1.1 to 1.4, P<0.001), and for subjects who had used only cannabis and no other drugs (adjusted odds ratio for linear trend 1.3, 1.1 to 1.5, p<0.015). the adjusted odds ratio for using cannabis >50 times was 6.7 (2.1 to 21.7) in the cannabis only group. Similar results were obtained when analysis was restricted to subjects developing schizophrenia after five years after conscription, to exclude prodromal cases. Conclusions. Cannabis use is associated with an increased risk of developing schizophrenia, consistent with a causal relation. This association is not explained by use of other psychoactive drugs or personality traits relating to social integration.
Bhattacharyya et al. (2012). Induction of psychosis by 9-Tetrahydrocannabinol reflects modulation of prefrontal and striatal function during attentional salience processing. Archives of General Psychiatry, 69(1), 27-36. doi: doi:10.1001/archgenpsychiatry.2011.161
Abstract: Context. The aberrant processing of salience is thought to be a fundamental factor underlying psychosis. Cannabis can induce acute psychotic symptoms, and its chronic use may increase the risk of schizophrenia. We investigated whether its psychotic effects are mediated through an influence on attentional salience processing. Objective. To examine the effects of 9-tetrahydrocannabinol (9-THC) and cannabidiol (CBD) on regional brain function during salience processing. Design. Volunteers were studied using event-related functional magnetic resonance imaging on 3 occasions after administration of 9-THC, CBD, or placebo while performing a visual oddball detection paradigm that involved allocation of attention to infrequent (oddball) stimuli within a string of frequent (standard) stimuli. Setting. University center. Participants. Fifteen healthy men with minimal previous cannabis use. Main Outcome. Measures Symptom ratings, task performance, and regional brain activation. Results. During the processing of oddball stimuli, relative to placebo, 9-THC attenuated activation in the right caudate but augmented it in the right prefrontal cortex. 9-Tetrahydrocannabinol also reduced the response latency to standard relative to oddball stimuli. The effect of 9-THC in the right caudate was negatively correlated with the severity of the psychotic symptoms it induced and its effect on response latency. The effects of CBD on task-related activation were in the opposite direction of those of 9-THC; relative to placebo, CBD augmented left caudate and hippocampal activation but attenuated right prefrontal activation. Conclusions. 9-Tetrahydrocannabinol and CBD differentially modulate prefrontal, striatal, and hippocampal function during attentional salience processing. These effects may contribute to the effects of cannabis on psychotic symptoms and on the risk of psychotic disorders.
Fergusson, D.M., Horwood, L.J., & Ridder, E.M. (2005). Tests of causal linkages between cannabis use and psychotic symptoms. Addiction, 100(3), 354-366.
Abstract: Aim. To examine possible causal linkages between cannabis use and psychosis using data gathered over the course of a 25-year longitudinal study. Design. A 25-year longitudinal study of the health, development and adjustment of a birth cohort of 1265 New Zealand children (635 males, 630 females). Setting. The Christchurch Health and Development Study, a general community sample. Participants. A total of 1055 participants from the Christchurch Health and Development Study (CHDS) cohort for whom data on cannabis use and psychotic symptoms were available on at least one occasion from 18, 21 and 25 years. Measurements. As part of this study, data were gathered on frequency of cannabis use and psychotic symptoms at ages 18, 21 and 25 years. Findings. Regression models adjusting for observed and non-observed confounding suggested that daily users of cannabis had rates of psychotic symptoms that were between 1.6 and 1.8 times higher (P < 0.001) than non-users of cannabis. structural equation modeling suggested that these associations reflected the effects of cannabis use on symptom levels rather than the effects of symptom levels on cannabis use. Conclusions. The results of the present study add to a growing body of evidence suggesting that regular cannabis use may increase risks of psychosis. The present study suggests that: (a) the association between cannabis use and psychotic symptoms is unlikely to be due to confounding factors; and (b) the direction of causality is from cannabis use to psychotic symptoms.
NEW! Goldschmidt, L., Richardson, G. A., Willford, J. A., Severtson, S. G., & Day, N. L. (2012). School achievement in 14-year-old youths prenatally exposed to marijuana. Neurotoxicology and Teratology, 34(1), 161-167.
Abstract: The relation between prenatal marijuana exposure (PME) and school achievement was evaluated in a sample of 524 14-year-olds. Women were recruited during pregnancy and assessed, along with their offspring, at multiple phases from infancy to early adulthood. The sample represents a low-income population. Half of the adolescents are male and 55% are African American. School achievement was assessed with the Wechsler Individual Achievement Test (WIAT) Screener (Psychological Corporation, 1992). A significant negative relation was found between PME and 14-year WIAT composite and reading scores. The deficit in school achievement was mediated by the effects of PME on intelligence test performance at age 6, attention problems and depression symptoms at age 10, and early initiation of marijuana use. These findings suggest that the effects of PME on adolescent achievement are mediated by the earlier negative effects of PME on child characteristics. The negative impact of these characteristics on adolescent achievement may presage later problems in early adulthood.
van Ours, J., & Williams, J. (2007, September 18). Cannabis use and educational attainment. VOX.
Martins, S.S., & Alexandre, P.K. (2009). The association of ecstasy use and academic achievement among adolescents in two US national surveys. Addictive Behaviors, 34(1), 9-16.
Abstract: The association of ecstasy (3, 4-methylenedioxymethamphetamine, MDMA) use with low academic achievement was examined in two nationally representative surveys of adolescents. We tested whether associations with low academic achievement were of similar magnitude or of stronger magnitude for ecstasy versus marijuana use (without ecstasy use), alcohol/tobacco use (without other drug use) and non-drug use in adolescence. Data from the adolescents in the 2002-2005 National Survey of Drug Use and Health (NSDUH, n= 65,294) and from the 2001-2003 Youth Risk Behavior Survey (YRBS, n= 27,592) were analyzed via weighted logistic regression models. Ecstasy, marijuana, and alcohol/tobacco use were associated with moderate and low academic achievement among adolescents in both surveys. Moreover, ecstasy was more strongly associated with low academic achievement and reporting that school gave no grades than alcohol/tobacco in both samples and than marijuana (NSDUH sample only). Prevention programs should inform adolescents that ecstasy use might impair their academic achievement.
Lynskey, M., & Hall, W. (2000). The effects of adolescent cannabis use on educational attainment: A review. Addiction, 9(5), 1621-1630.
Abstract: This paper reviews research examining the link between cannabis use and educational attainment among youth. Cross-sectional studies have revealed significant associations between cannabis use and a range of measures of educational performance including lower grade point average, less satisfaction with school, negative attitudes to school, increased rates of school absenteeism and poor school performance. However, results of cross-sectional studies cannot be used to determine whether cannabis use causes poor educational performance, poor educational performance is a cause of cannabis use or whether both outcomes are a reflection of common risk factors. Nonetheless, a number of prospective longitudinal studies have indicated that early cannabis use may significantly increase risks of subsequent poor school performance and, in particular, early school leaving. This association has remained after control for a wide range of prospectively assessed covariates. Possible mechanisms underlying an association between early cannabis use and educational attainment include the possibility that cannabis use induces an 'amotivational syndrome' or that cannabis use causes cognitive impairment. However, there appears to be relatively little empirical support for these hypotheses. It is proposed that the link between early cannabis use and educational attainment arises because of the social context within which cannabis is used. In particular, early cannabis use appears to be associated with the adoption of an anti-conventional lifestyle characterized by affiliations with delinquent and substance using peers, and the precocious adoption of adult roles including early school leaving, leaving the parental home and early parenthood.
Ellickson, P. L., Bui, K., Bell, R., & McGuigan, K. (1998). Does early drug use increase the risk of dropping out of high school? Journal of Drug Issues, 28(2), 357-380.
Abstract: This study examines the impact of early adolescent drug use on subsequent dropping out of high school in a sample of 4,390 adolescents from California and Oregon. Participants were initially surveyed in 7th grade in 1985 and again in 1990 when they should have completed 12th grade. Logistic regression analyses show that frequency of cigarette use during 7th grade predicts dropping out of high school, controlling for demographics, family structure, academic orientation, early deviance, and school environment. Separate analyses by race/ethnicity replicate this finding for Asians, Blacks, and whites, but not for Latinos. For Latinos, early marijuana use predicts dropping out. The results suggest that preventing or reducing the incidence of early smoking and marijuana use may help reduce the probability of dropping out of high school.
Hunt, J., Eisenberg, D., & Kilbourne, A.M. (2010). Consequences of receipt of a psychiatric diagnosis for completion of college. Psychiatric Services, 61(4), 399-404.
Abstract: The purpose of this study was to evaluate the independent associations between DSM-IV psychiatric disorders and the failure to complete college among college entrants. Methods. Data were from the 2001-2002 National Epidemiologic Survey on Alcohol and Related Conditions (NESARC). The sample included 15,800 adults, aged 22 years and older, who at least entered college. Diagnoses were made with the NESARC survey instrument, the Alcohol Use Disorder and Associated Disability Interview Schedule-DSM-IV Version. The large sample permitted analysis of multiple psychiatric disorders in the same multivariable logistic regression models. Given the frequent comorbidity of these disorders, this approach is an important step toward disentangling the independent roles of disorders in postsecondary educational outcomes. Results. Evaluation of the independent associations between specific psychiatric disorders and postsecondary educational attainment showed that five diagnoses were positively and significantly associated with the failure to graduate from college. Four were axis I diagnoses: bipolar I disorder, marijuana use disorder, amphetamine use disorder, and cocaine use disorder. One was an axis II diagnosis: antisocial personality disorder. Conclusions. This study provides new data on DSM-IV diagnoses associated with the failure to complete postsecondary education. The findings suggest that psychiatric factors play a significant role in college academic performance, and the benefits of prevention, detection, and treatment of psychiatric illness may therefore include higher college graduation rates.
Pinchevsky, G.M., Arria, A.M., Caldeira, K.M., Garnier-Dykstra, L.M., Vincent, K.B., & O'Grady, K. (2011). Marijuana exposure opportunity and initiation during college: Parent and peer influence. Prevention Science. DOI 10.1007/s11121-011-0243-4
Abstract: Marijuana is the most prevalent illicit drug used by adolescents and young adults, yet marijuana initiation is rarely studied past adolescence. The present study sought to advance our understanding of parent and peer influences on marijuana exposure opportunity and incident use during college. A sample of 1,253 students was assessed annually for 4 years starting with the summer prior to college entry. More than one-third (38%(wt)) of students had already used marijuana at least once prior to college entry; another 25%(wt) initiated use after starting college. Of the 360 students who did not use marijuana prior to college, 74% were offered marijuana during college; of these individuals, 54% initiated marijuana use. Both low levels of parental monitoring during the last year of high school and a high percentage of marijuana-using peers independently predicted marijuana exposure opportunity during college, holding constant demographics and other factors (AOR_=_0.92, 95% CI_=_0.88-0.96, p_<_.001 and aor_=_1.11, 95% ci_=_1.08-1.14, p_<_.001, respectively). among individuals with exposure opportunity, peer marijuana use (aor_=_1.04, 95% ci_=_1.03-1.05, p_<_.001), but not parental monitoring, was associated with marijuana initiation. results underscore that peer influences operate well into late adolescence and young adulthood and thus suggest the need for innovative peer-focused prevention strategies. parental monitoring during high school appears to influence exposure opportunity in college; thus, parents should be encouraged to sustain rule-setting and communication about adolescent activities and friend selection throughout high school.
Kelly, K.J., Comello, M.L. & Hunn, L.C.. (2002). Parent-child communication, perceived sanctions against drug use, and youth drug involvement. Adolescence, 37(148), 775-787.
Abstract: To explore the relationship of parent-child communication to youth drug involvement, we analyzed secondary data from substance-abuse surveys given to 82,918 7th-12th graders in the U.S. It was found that: (a) parents are most often identified as the individuals who have talked to a child about drugs; (b) youth consider parents to be credible sources of information about drugs; (c) as perceived family sanctions go up, drug involvement goes down; (d) youth with the highest levels of drug involvement are the group most likely both to have had no one talk to them and to have had the largest number of people talk to them about drugs; and (e) perceived family sanctions increase dramatically for highly drug-involved youth once they have been talked to by one person.
Martin, K. R. (2003). Youths' opportunities to experiment influence later use of illegal drugs. NIDA Notes, 17(5).
Partnership for a Drug-Free America & MetLife Foundation. (2010). 2009 Parents and Teens Attitude Tracking Study Report.
SADD (Students Against Destructive Decisions) and Liberty Mutual. (2005). Teens Today 2005.
Monitoring the Future: national surveys of 8th, 10th, and 12th graders
Substance Abuse and Mental Health Services Administration's National Survey on Drug Use and Health.