Legal Pot: Good for Public Safety, But Not for Mental Health?

Two new studies of the impact of state legalization of marijuana offer a mixed verdict. One uncovered an association between legal pot and increased crime clearance, while the other detected a correlation between legalization and the frequency of serious mental illnesses.

While the sale and possession of marijuana remain federal offenses, the state-level impact of legalization on public health and safety has been hotly debated.

Two new studies demonstrate that legalization can be a mixed bag: one finds a correlation between legalization and the frequency of serious mental illnesses, while the other uncovers an association between legalization and increased crime clearance.

Advocates have long asserted that police effectiveness would increase if marijuana were legal, because officers would have more time and resources to devote to other offenses.

In “Marijuana Legalization and Crime Clearance Rates: Testing Proponent Assertions in Colorado and Washington State,” researchers find that this claim holds up under scrutiny.

The paper, published this month in Police Quarterly, notes significant increases in the clearance rate—the ratio between the number of crimes solved and the total number of crimes recorded by the police—for violent crime in both Colorado and Washington state, the first two states to legalize recreational cannabis, following legalization.

The data did not allow the study’s authors to attribute the increased clearance rate to legalization or to posit why the observed trend occurred. But the timing and the lack of other probable explanations lead them to hypothesize that legalization did indeed enable officers to focus on other crimes.

Notably, national trends remained relatively flat during the time period examined, and there were no kinds of crime in either state for which legalization negatively impacted clearance rates.

The authors of the paper, all from Washington State University, were David A. Makin, Dale W. Willits, Guangzhen Wu, Kathryn O. DuBois, Ruibin Lu, Mary K. Stohr, Wendy Koslicki, Duane Stanton, Craig Hemmens, John Snyder and Nicholas P. Lovrich.

But if legalization boosts public safety, it appears to strike a small but not insignificant blow to mental health.

Medical Cannabis Legalization and State-Level Prevalence of Serious Mental Illness in the National Survey on Drug Use and Health 2008-2015,” published this month in the International Review of Psychiatry, finds that legalization is positively associated with instances of serious mental illness in states with “liberal” laws, i.e. laws permitting cannabis use for a broad range of medical conditions.

The prevalence of serious mental illnesses was 0.3 percent higher in states with liberal laws compared with other states once cannabis use was taken into account.

Previous research has linked high levels of cannabis consumption with psychotic disorders. Citing such studies, researchers hypothesize that legalization leads to increased use among state residents, which increases users’ likelihood of developing psychosis.

The study’s authors were Lauren M. Dutra, William J. Parish, Camille K. Gourdet , and Jennie L. Wiley, all of RTI International; and Sarah A. Wylie of the Oregon Health Authority.

Nearly half of Americans currently live in states where marijuana use is legal in some form. Authors from both studies stressed the need for further research to verify their claims and to determine what the effects of legalization truly are.

Elena Schwartz is a TCR news intern. Readers’ comments are welcome.