Medical Marijuana Laws and Suicides by Gender and Age

D. Mark Anderson, PhD; Daniel I. Rees, PhD; Joseph J. Sabia, PhD

Disclosures

Am J Public Health. 2014;104(12):2369-2376. 

In This Article

Discussion

Opponents of legalizing medical marijuana point to the large number of studies showing that marijuana use is positively associated with depression, the onset of panic attacks, psychosis, schizophrenia, and suicidal ideation.[10,11,39–46] However, the association between marijuana use and outcomes such as these could be attributable to difficult-to-measure confounders such as personality.[12] Moreover, estimates produced by nonprospective studies could reflect reverse causation stemming from self-medication.[10,13,47] Although there have been attempts to account for these potential sources of statistical bias, none have been particularly convincing. In fact, a recent review of the literature noted that the majority of studies in this area "did not adequately address the problem of reverse causation as a possible alternative explanation for any association observed."[11(p325)]

The current study avoided the problems of reverse causality and difficult-to-measure confounders by comparing the change in suicides per 100 000 population that occurred after the legalization of medical marijuana with the change in suicides per 100 000 population for a set of control states. This estimation approach can be thought of as exploiting a "natural experiment" unrelated to comorbidities or personality.

The graphical analysis provided evidence that, before legalization, male suicides in the treated states evolved in a similar fashion to male suicides in the control states. After legalization, these trends diverged. Specifically, the male suicide rate in medical marijuana states fell, but the male suicide rate increased, albeit modestly, in the control states. Formal estimates obtained with regression analysis were consistent with the graphical analysis. These estimates suggested that the legalization of medical marijuana was associated with a 9.2% to 10.8% decrease in the suicide rate of men aged 20 through 29 years, and a 9.4% to 13.7% decrease in the suicide rate of men aged 30 through 39 years. These estimates were generally robust to adjustment for linear time trends at the state level.

The graphical analysis showed that female suicide rates in medical marijuana states and the control states followed very similar trajectories. Estimates obtained with regression analysis confirmed this result. In general, estimates of the relationship between the legalization of medical marijuana and female suicide rates were negative, but these estimates were less precise than the estimates obtained for males and were sensitive to model specification, a pattern of results attributable, perhaps, to gender differences in frequency of substance use,[48–50] physiological responses to cannabinoids,[14–16] or underlying health conditions such as panic and personality disorders.[51] Frequency of marijuana use is associated with social anxiety,[50] and prospective studies have shown that marijuana participation is positively related to panic attacks,[45,46] which in turn are positively associated with suicidal ideation and a history of attempted suicide.[52]

Suicide among adolescents and young adults is often triggered by stressful life events. Stressful life events include, but are not limited to, the breakup of a romantic relationship,[53–56] conflict with a parent or sibling,[54,56] an abortion,[57,58] and legal or disciplinary problems.[54] Among older adults, problems at work, financial difficulties, unemployment, and separation or divorce are common triggers of suicide.[59–64] Among the elderly, suicide is often associated with physical illness and functional impairment.[65–69]

The results of the current study are consistent with the hypothesis that legalizing medical marijuana leads to increased marijuana use, which in turn helps individuals cope with stressful life events. There is anecdotal evidence that much of the medical marijuana crop is diverted to the illegal market, increasing availability and lowering price.[70–72] This anecdotal evidence is supported by recent studies showing that the legalization of medical marijuana leads to increased arrests for marijuana possession among 18- through 39-year-olds, increased admissions to federally funded treatment centers for marijuana use, and a 10% to 26% reduction in the price of high-quality marijuana.[5,6] However, despite claims that marijuana can be an effective treatment of depression and panic disorders,[73–75] there is no scientific evidence that it can be used to cope with stressful life events.

Alcohol consumption represents an alternative route through which the legalization of medical marijuana could potentially have an impact on suicides. A recent study showed that the legalization of medical marijuana was associated with substantial decreases in alcohol participation and binge drinking among young adults.[5] Binge drinking is considered to have "especially high social and economic costs"[76(p70)] and is associated with suicidal ideation.[77,78] Moreover, alcoholism is more common among individuals with major depression,[79] and is associated with suicidal ideation as well as attempted and completed suicides.[80,81]

Study Strengths and Weaknesses

To our knowledge, this was the first study to examine the relationship between legalizing medical marijuana and suicides. Previous studies have documented a positive association between marijuana use and outcomes such as depression and suicidal ideation.[1–3] However, this association could be attributable to difficult-to-measure confounders or reflect self-medication.[10,12,13] By comparing the change in suicides after the legalization of medical marijuana with the change in suicides for a set of control states, we avoided the problems of reverse causality and difficult-to-measure confounders.

Important study limitations warrant mention. First, the Mortality Detail Files were available only through 2007 when the statistical analysis was conducted. Since 2007, 9 states (Arizona, Connecticut, Delaware, Illinois, New Hampshire, Maryland, Massachusetts, Michigan, and New Jersey) have legalized medical marijuana. These 9 states, although included in our sample, did not contribute to the identification of the estimates reported in Table 1 and Table 2.

Second, the exact date on which any given suicide took place was not available. Therefore, if a state legalized marijuana during the middle of the year (as opposed to January 1 or December 31), then the legalization indicator was assigned a fractional value. For instance, if legalization occurred on June 30, then it took on a value of 0.5. Although standard, this approach could have biased the estimates in Table 1 and Table 2 toward 0 by introducing measurement error. In other words, it is possible that the impact of legalizing medical marijuana on suicides is larger than that suggested by the estimates contained in Table 1 and Table 2.

Third, the data on suicides from the Mortality Detail Files are at the state and year level. Although the gender and the age of individuals who committed suicide are available, nothing was known about their mental health before the legalization of medical marijuana nor was there information on whether an individual smoked marijuana or consumed alcohol before the legalization of medical marijuana.

Finally, Alaska, Hawaii, Maine, New Mexico, and Vermont limited caregivers to 1 medical marijuana patient or prohibited home cultivation altogether. Distinguishing between these 5 states and states with less restrictive medical marijuana laws produced estimates that were not sufficiently precise to reject the hypothesis that legalization had a similar impact on male suicides regardless of whether caregivers were limited to 1 medical marijuana patient, a result likely driven by lack of statistical power. Because the majority of states that legalized medical marijuana during the period 1990 to 2007 were located in the western half of the United States, where suicide rates are highest,[82] our results may not extend to other regions of the country. Several northeastern states including Connecticut, Massachusetts, and New Jersey have legalized medical marijuana since 2007. Whether they will experience a reduction in suicides is an open question.

Implications and Conclusions

To date, 21 states have adopted medical marijuana laws. Although these laws almost certainly have important public health implications, we know very little about their effects.

The current study found a strong negative relationship between the legalization of medical marijuana and suicides among young men. This relationship is consistent with the often-voiced, but controversial claim that marijuana can be used to cope with depression and anxiety caused by stressful life events.[42,73–75,83,84] However, it may, at least in part, be attributable to the reduction in alcohol consumption among young adults that appears to accompany the legalization of medical marijuana.[5] Although marijuana and alcohol use are positively correlated in the cross-section,[85,86] there is evidence of a sharp decrease in marijuana use when individuals reach the minimum legal drinking age, suggesting that young adults substitute marijuana for alcohol.[87] There is also evidence that restricting access to alcohol leads to fewer suicides.[29–31,88] The precise mechanism thorough which legalizing medical marijuana is related to suicides among men aged 20 to 39 years remains a topic for future study.

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