Since 2012, 18 states and the nation’s capital have legalized recreational marijuana, even as it remains illegal under federal law. A new working paper released through the National Bureau of Economic Research has made a few of the consequences of this policy shift clearer.

The upshot is that marijuana legalization poses an obvious tradeoff: marijuana use goes up, while marijuana arrests go down. Most other hypothesized consequences, good and bad, remain uncertain. Alongside some clear conclusions, the paper has lots of imprecise, statistically insignificant findings.

In general, papers like this one analyze how trends differed between states that changed their marijuana laws and those that did not. For each outcome, the authors run the numbers a few ways, allowing readers to see how sensitive the results are to changes in the statistical models.

One commonsense effect of these policies is that pot use increases—at least according to self-report surveys, which remain (unfortunately) the best method we have for measuring the phenomenon. With legalization, the share of adults reporting pot use in the past 30 days increases by 1.6 to 3.6 percentage points, a 20 percent–40 percent gain from previous levels. This is concerning because, while pot is nowhere near as dangerous as some other drugs, it does have some negative effects on health and behavior.

The other obvious consequence of legalizing pot is that, well, pot is legal, and people aren’t arrested for it anymore, so long as they are of age and stay within the confines imposed by the new laws. According to the study, pot-possession arrests decline by more than 90 percent after legalization. Other drug arrests might decline somewhat as well, suggesting that states that legalize pot may also start taking a generally more lenient stance toward drugs.

The situation is less clear when it comes to other consequences that supporters and critics of these laws have suggested. For example, legal pot could in theory change arrest rates for other crimes, because legal pot drives people to commit crimes; because police have the resources to pursue other problems; or because diminishing the black market reduces crime. But the study detects little change in arrests for violent or property crime. Further research might also consider reports of crime, both to the police and in victimization surveys, to disentangle effects that might cut in opposite directions.

Another common theory is that legal pot will affect the use of harder drugs, either via a “gateway” effect (graduating from pot to worse things) or via “substitution” (using marijuana instead of other drugs). The authors report that legal pot doesn’t seem to increase use of, treatment admissions for, or deaths from hard drugs in general, and that the laws might even reduce opioid deaths.

However, the results on opioid deaths are imprecise and mostly statistically insignificant. This idea also has a tricky history in the literature. A 2014 study claimed that medical-marijuana laws reduced the toll of the opioid epidemic, but a 2019 study using the same methods found that, when later data were added to the model, the relationship not only weakened but reversed. There are various reasons why the effect might change over time or why recreational and medical pot laws might have different effects. Skepticism is warranted.

Further, while numerous studies have reported that users substitute marijuana for alcohol, this study finds no measurable change in binge drinking, alcohol-treatment admissions, or alcohol-related deaths for states that legalize pot.

Recreational-marijuana laws are less than a decade old. As time passes, we will learn more about longer-term effects and collect enough data to detect smaller effects than we can now. For the time being, we know that the tradeoffs suggested by common sense are real: fewer arrests, more pot smoking.

Photo by ANGELA WEISS/AFP via Getty Images


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