Study: Recreational and Medical Marijuana Laws Linked to 9–11% Drop in Daily Opioid Misuse Among People Who Inject Drugs

A study published in the journal Drug and Alcohol Dependence by researchers from Boston University School of Public Health, Emory University, Johns Hopkins University, and Florida State University found that states with both medical and recreational marijuana laws experienced measurable reductions in daily opioid misuse among people who inject drugs (PWID), a population at the center of the nation’s overdose crisis. The study analyzed data from 28,069 PWID across 13 states using four waves of CDC National HIV Behavioral Surveillance surveys conducted between 2012 and 2022. Researchers used a staggered difference-in-differences model to compare states that had only legalized marijuana for medical use with those that later legalized adult use as well.

They found that transitioning from medical-only laws to states allowing both medical and recreational marijuana was associated with a 9% to 11% reduction in the probability of daily non-medical opioid use. The reduction was even more pronounced when looking specifically at injected opioids, where the probability dropped between 2% and 19% depending on the model used.

In contrast, states that adopted only medical marijuana laws did not show the same reduction.

Researchers also examined how legalization influenced daily marijuana use among PWID. While no overall increase was observed across the full sample, daily marijuana use did rise among non-Hispanic White participants in states transitioning from prohibition to medical legalization, increasing from roughly 15% to 20%.

The authors note that people who use opioids often report turning to marijuana to manage withdrawal symptoms, reduce cravings, and support recovery efforts. Prior research cited in the paper has linked frequent marijuana use among PWID with injecting opioids less often and with improved retention in opioid treatment programs, both of which are associated with lower overdose risk.

The study also highlights racial disparities in how legalization may affect substance use patterns. While marijuana use increased among non-Hispanic White participants following legalization, the same pattern was not observed among Black participants, raising questions about whether structural inequities influence who benefits from cannabis reform.

The sample in the study was economically vulnerable, with 78% living at or below the federal poverty line and 64% experiencing houselessness in the prior year. Forty-one percent of participants were Black, 39% were White, and 19% were Hispanic or Latino.

Researchers emphasize that most previous studies examining marijuana policy and opioid use have focused on the general population, not people who inject drugs. This analysis, they say, helps fill that gap by examining the group most directly affected by overdose risk.

While the authors caution that the study is observational and cannot prove causation, they conclude that broader marijuana legalization may be associated with meaningful reductions in daily opioid misuse among PWID and could play a role in reducing drug-related harms if paired with equitable access and supportive public health policies.