Legalizing medical marijuana has either decreased or had no effect on teenage cannabis use, and initial evidence suggests that recreational legalization has similar effects, according to a new comprehensive review of studies on the topic.
The working paper, published by the National Bureau of Economic Research in April, also explores literature around the effects of medical and recreational marijuana legalization on other public health outcomes including tobacco smoking, use of opioids and other prescription drugs, traffic fatalities and overall crime. It considers results from more than 140 studies.
"The section of the paper that I think is most interesting to researchers across fields, across disciplines, is youth or teen marijuana use," said lead author Mark Anderson, an associate professor at Montana State University. "There's just no evidence that teen use has been encouraged through the legalization of marijuana for medical purposes."
In fact, several of the studies reviewed by Anderson and co-author Daniel Rees from the University of Colorado at Boulder showed declines in teen marijuana use associated with medical legalization. Initial research on recreational legalization shows similar effects, but since fewer states have had recreational marijuana laws for less time, the literature around the issue is smaller and less conclusive, according to Anderson.
Thirty-six states had legalized medical marijuana and 14 had legalized recreational use at the time the paper was written. New York Gov. Andrew Cuomo signed a law legalizing recreational marijuana use in the state shortly before the paper was published by NBER, bringing the number of states with legal recreational cannabis up to 15.
The New York recreational law is uniquely liberal, allowing some cafes to sell marijuana that customers can consume on-site as long as the establishments do not also serve alcohol.
Anderson said his literature review shows evidence that marijuana is functioning as a substitute for alcohol in areas where it has been legalized. The review references survey-based studies, as well as studies using alcohol sales data, to support this assertion.
"The more and more research that comes out on the relationship between marijuana legalization and alcohol suggests that these two are substitutes," he said. "When you legalize marijuana, especially among young adults, it really appears that alcohol use falls."
This substitution effect can also lead to decreased traffic fatalities in states that have legalized medical marijuana, multiple studies have found. Anderson and Rees, along with Benjamin Hansen, first discovered this effect in a 2013 Journal of Law & Economics paper. Their findings were corroborated in a 2020 American Journal of Public Health paper.
"When we were researching this topic, admittedly I was a little surprised," Anderson said. "My priors suggested this wasn't the result we were going to find."
While evidence that medical marijuana legalization reduces traffic fatalities is "fairly conclusive," Anderson said, the relationship between recreational legalization and traffic deaths needs more research.
"Readers are unsatisfied when they hear the jury's still out, but in many places that's the case," said Anderson in reference to the public health effects of recreational legalization.
Elsewhere in the paper, Anderson and Rees wrote that medical marijuana legalization appears to have decreased opioid-related deaths, decreased tobacco use and decreased use of prescription drugs for issues like sleep and anxiety, although these areas have been subject to less research.
While medical marijuana legalization has somewhat conclusively been shown to lower overall crime, according to Anderson and Rees, the pair of researchers said further studies should be conducted on the localized effects of marijuana dispensaries on crime.
"The research on local effects around dispensaries is more mixed and it's more nuanced," said Anderson. "I think this is where ... a lot of future research needs to go."
As an NBER working paper, Anderson and Rees' work has not been subject to peer review. But several other leading marijuana researchers contacted by The Academic Times spoke highly of their paper.
"This is a balanced piece that explicitly recognizes the heterogeneity of results while also providing a clear sense of where the preponderance of the evidence suggests a clear conclusion," said Harvard University senior economics lecturer and director of undergraduate studies Jeffrey Miron, who has written extensively about marijuana policy.
Jacqueline Doremus, an economist at California Polytechnic State University who has examined the effects of marijuana legalization on sales of over-the-counter sleep aids and acid reflux drugs, said, "This paper is vital to help us synthesize a sprawling literature where small differences in an analysis can really affect results."
And Sietse Goffard, an economist who has studied various aspects of marijuana legalization for the Cato Institute, called the review "very comprehensive and well researched."
The working paper, "The Public Health Effects of Legalizing Marijuana," published in April by the National Bureau of Economic Research, was authored by D. Mark Anderson, Montana State University; and Daniel I. Rees, University of Colorado at Denver.