Prospective Cohort Study

Recent years have seen a rapid rise in the medical and recreational use of cannabis: a broad term that can be used to describe the various products and chemical compounds (e.g., marijuana, cannabinoids) derived from different species of the cannabis plant. Despite increased cannabis use and a changing state-level policy landscape, conclusive evidence regarding the shortand long-term health effects—both harms and benefits—of cannabis use remains elusive.

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The Health Effects of Cannabis and Cannabinoids: The Current State of Evidence and Recommendations for Research

Importance Laws and attitudes toward marijuana in the United States are becoming more permissive but little is known about whether the prevalence rates of marijuana use and marijuana use disorders have changed in the 21st century. Objective To present nationally representative information on the past-year prevalence rates of marijuana use, marijuana use disorder, and marijuana use disorder among marijuana users in the US adult general population and whether this has changed between 2001-2002 and 2012-2013. Design, Setting, and Participants Face-to-face interviews conducted in surveys of 2 nationally representative samples of US adults: the National Epidemiologic Survey on Alcohol and Related Conditions (data collected April 2001-April 2002; N = 43 093) and the National Epidemiologic Survey on Alcohol and Related Conditions–III (data collected April 2012-June 2013; N = 36 309). Data were analyzed March through May 2015. Main Outcomes and Measures Past-year marijuana use and DSM-IV marijuana use disorder (abuse or dependence). Results The past-year prevalence of marijuana use was 4.1% (SE, 0.15) in 2001-2002 and 9.5% (SE, 0.27) in 2012-2013, a significant increase ( P DSM-IV marijuana use disorder was 1.5% (0.08) in 2001-2002 and 2.9% (SE, 0.13) in 2012-2013 ( P P Conclusions and Relevance The prevalence of marijuana use more than doubled between 2001-2002 and 2012-2013, and there was a large increase in marijuana use disorders during that time. While not all marijuana users experience problems, nearly 3 of 10 marijuana users manifested a marijuana use disorder in 2012-2013. Because the risk for marijuana use disorder did not increase among users, the increase in prevalence of marijuana use disorder is owing to an increase in prevalence of users in the US adult population. Given changing laws and attitudes toward marijuana, a balanced presentation of the likelihood of adverse consequences of marijuana use to policy makers, professionals, and the public is needed.

https://jamanetwork.com/journals/jamapsychiatry/articlepdf/2464591/yoi150057.pdf

Prevalence of Marijuana Use Disorders in the United States Between 2001-2002 and 2012-2013.

The difference in difference (DID) design is a quasi-experimental research design that researchers often use to study causal relationships in public health settings where randomized controlled trials (RCTs) are infeasible or unethical. However, causal inference poses many challenges in DID designs. In this article, we review key features of DID designs with an emphasis on public health policy research. Contemporary researchers should take an active approach to the design of DID studies, seeking to construct comparison groups, sensitivity analyses, and robustness checks that help validate the method's assumptions. We explain the key assumptions of the design and discuss analytic tactics, supplementary analysis, and approaches to statistical inference that are often important in applied research. The DID design is not a perfect substitute for randomized experiments, but it often represents a feasible way to learn about casual relationships. We conclude by noting that combining elements from multiple quasi-experimental techniques may be important in the next wave of innovations to the DID approach.

Designing Difference in Difference Studies: Best Practices for Public Health Policy Research

Cannabis use has been reported to induce long-lasting psychotic disorders and a dose-response relationship has been observed. We performed a systematic review of studies that investigate the association between the degree of cannabis consumption and psychosis and a meta-analysis to quantify the magnitude of effect. Published studies were identified through search of electronic databases, supplemented by manual searches of bibliographies. Studies were considered if they provided data on cannabis consumption prior to the onset of psychosis using a dose criterion (frequency/amount used) and reported psychosis-related outcomes. We performed random effects meta-analysis of individual data points generated with a simulation method from the summary data of the original studies. From 571 references, 18 studies fulfilled inclusion criteria for the systematic review and 10 were inserted in the meta-analysis, enrolling a total of 66 816 individuals. Higher levels of cannabis use were associated with increased risk for psychosis in all the included studies. A logistic regression model gave an OR of 3.90 (95% CI 2.84 to 5.34) for the risk of schizophrenia and other psychosis-related outcomes among the heaviest cannabis users compared to the nonusers. Current evidence shows that high levels of cannabis use increase the risk of psychotic outcomes and confirms a dose-response relationship between the level of use and the risk for psychosis. Although a causal link cannot be unequivocally established, there is sufficient evidence to justify harm reduction prevention programs.

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Meta-analysis of the Association Between the Level of Cannabis Use and Risk of Psychosis

To date, 19 states have passed medical marijuana laws, yet very little is known about their effects. The current study examines the relationship between the legalization of medical marijuana and traffic fatalities, the leading cause of death among Americans ages 5–34. The first full year after coming into effect, legalization is associated with an 8–11 percent decrease in traffic fatalities. The impact of legalization on traffic fatalities involving alcohol is larger and estimated with more precision than its impact on traffic fatalities that do not involve alcohol. Legalization is also associated with sharp decreases in the price of marijuana and alcohol consumption, which suggests that marijuana and alcohol are substitutes. Because alternative mechanisms cannot be ruled out, the negative relationship between legalization and alcohol-related traffic fatalities does not necessarily imply that driving under the influence of marijuana is safer than driving under the influence of alcohol.

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Medical Marijuana Laws, Traffic Fatalities, and Alcohol Consumption

This paper examines the relationship between the minimum high school dropout age and juvenile arrest rates by exploiting state-level variation in dropout age laws. County-level arrest data for the period 1980 to 2008 and difference-in-difference-in-difference-type empirical strategy are used to compare the arrest rates over time of various age groups within counties that differ by their state's minimum dropout age. The evidence suggests that minimum dropout age requirements have a significant and negative effect on property and violent crime arrest rates for individuals 16 to 18 years old. The results are consistent with an incapacitation effect of schooling.

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In School and Out of Trouble? The Minimum Dropout Age and Juvenile Crime

While at least a dozen state legislatures are considering bills to allow the consumption of marijuana for medicinal purposes, the federal government has recently intensified its efforts to close medical marijuana dispensaries Federal officials contend that the legalization of medical marijuana encourages teenagers to use marijuana and have targeted dispensaries operating within 1,000 feet of schools, parks and playgrounds Using data from the national and state Youth Risk Behavior Surveys, the National Longitudinal Survey of Youth 1997 and the Treatment Episode Data Set, we estimate the relationship between medical marijuana laws and marijuana use Our results are not consistent with the hypothesis that legalization leads to increased use of marijuana by teenagers

Medical Marijuana Laws and Teen Marijuana Use

Objectives. We estimated the association between legalizing medical marijuana and suicides.Methods. We obtained state-level suicide data from the National Vital Statistics System’s Mortality Detail Files for 1990–2007. We used regression analysis to examine the association between medical marijuana legalization and suicides per 100 000 population.Results. After adjustment for economic conditions, state policies, and state-specific linear time trends, the association between legalizing medical marijuana and suicides was not statistically significant at the .05 level. However, legalization was associated with a 10.8% (95% confidence interval [CI] = −17.1%, −3.7%) and 9.4% (95% CI = −16.1%, −2.4%) reduction in the suicide rate of men aged 20 through 29 years and 30 through 39 years, respectively. Estimates for females were less precise and sensitive to model specification.Conclusions. Suicides among men aged 20 through 39 years fell after medical marijuana legalization compared with those in states that did ...

Medical marijuana laws and suicides by gender and age.

Last fall, voters in Colorado and Washington approved measures legalizing the recreational use of marijuana. In the near future, residents of these states who are 21 years of age and older will be able to purchase marijuana at retail stores (Donlan, 2013). Although it can be challenging to predict future behavior, Mark Kleiman, a prominent drug policy expert, described what might be characterized as the worstcase scenario. According to Kleiman, this scenario would involve three elements: more heavy drinking, “carnage on our highways,” and a “massive” increase in the use of marijuana by minors (Livingston, 2013). Below, we discuss the likely effects of legalizing marijuana for recreational use on alcohol consumption, traffic fatalities, substance use among high school students, and other outcomes of interest to policymakers and the public. Our discussion draws heavily on studies that have examined the legalization of medical marijuana. These studies are relevant because, in states such as California, Colorado, Oregon, and Washington, the legalization of marijuana for medicinal purposes approaches de facto legalization of marijuana for recreational purposes. One of the key unknowns in the debate over legalization concerns the relationship between alcohol and marijuana use. Researchers have attempted to produce causal estimates of this relationship by exploiting cross-sectional policy and price variation (Pacula, 1998; Williams et al., 2004). We note that these estimates could easily be spurious and that more reliable estimates based on clearly defined natural experiments show that alcohol and marijuana are substitutes. Because the social costs associated with the consumption of alcohol clearly outweigh those associated with the consumption of marijuana, we conclude that legalizing the recreational use of marijuana is likely to improve public health, although plenty of unanswered questions remain.

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D. Mark Anderson

Papers

Medical Marijuana Laws, Traffic Fatalities, and Alcohol Consumption

In School and Out of Trouble? The Minimum Dropout Age and Juvenile Crime

Medical Marijuana Laws and Teen Marijuana Use

Medical marijuana laws and suicides by gender and age.

The Legalization of Recreational Marijuana: How Likely Is the Worst‐Case Scenario?