Another study for the “pros” column of the pro-con list for cannabis legalization just hit the research journals, and this one could save lives. A Boston University School of Public Health study published in Drug and Alcohol Dependence found that states legalizing cannabis for both medical and adult use saw a 9-to-11 percentage point decline in daily opioid use among people who inject drugs compared to medical-only states.
Let that sink in. We’re talking about a population at the epicenter of America’s opioid crisis – where opioids account for over 75 percent of fatal drug overdoses – finding a safer alternative in legal cannabis.
Study Finds Cannabis Legalization Could Reduce Daily Opioid Use
Researchers analyzed data from the CDC’s National HIV Behavioral Surveillance, tracking nearly 29,000 people who inject drugs across 13 states over four waves (2012, 2015, 2018, and 2022). The findings were consistent across all racial and ethnic groups, as well as among both males and females.
“The magnitude of decrease in opioid use that we observed among a population that is experienced with opioid use and likely to experience unpleasant withdrawal symptoms after reducing this use is very profound and important,” says Dr. Danielle Haley, the study’s lead author and assistant professor of community health sciences at BUSPH.
What makes this even more significant? The study focused on people who inject drugs—a group that stands to benefit most from policies expanding cannabis access. Previous research has primarily looked at the general population, which has a lower risk of opioid-related harms, with mixed results.
Why Legal Cannabis Seems to Reduce Opioid Use
Dr. Haley’s team points to a crucial factor: creating a safe, regulated supply matters. “Legalized cannabis tends to be higher quality and more potent. As these products become more available and cheaper, people might be able to reduce their opioid use even without increasing how often they use cannabis,” Haley explains.
The study found no evidence that dispensaries increase local cannabis crimes or intoxication-related offenses. Instead, the regulated market appears to be displacing the unstable and toxic illegal opioid supply with a comparatively safer option.
One interesting nuance: while the team didn’t observe overall links between cannabis legalization and daily cannabis use, White participants in medical-only states showed a 5 percentage point increase. Researchers suggest this reflects long-standing racial inequities in healthcare access that make it easier for White people to navigate medical cannabis systems.
The Policy Context
This research drops at a pivotal moment. In December 2025, President Donald Trump signed an executive order to downgrade cannabis from Schedule 1 to Schedule 3—a significant shift that will lower federal restrictions on the plant. Nearly all U.S. states and Washington, D.C. have legalized medical cannabis, while 48 percent of states now allow adult recreational use.
“What this study shows is the potential impact of decriminalization paired with access to a regulated supply,” says Stephen Murray, adjunct clinical assistant professor at BUSPH and an overdose survivor. “When legal barriers are removed and people have safer alternatives available, we see meaningful reductions in daily opioid use—even among people with long histories of injection drug use. That’s a powerful signal.”
The Bottom Line
While prohibitionists continue to debate the harms and benefits of cannabis reform, the data keeps piling up in favor of legalization. This study adds another critical piece to the puzzle: widespread cannabis access may enable people to substitute dangerous opioids with a safer alternative, potentially reducing overdose deaths in communities hit hardest by the crisis
When even police are calling on the government for change, studies like this only add to the potential benefits outweighing the so-called risks. This isn’t the first study to find a correlation between legalization and reduced opiate use. This study was more narrow in scope and left researchers recommending future studies investigate similar links between legal cannabis and other harm reduction outcomes, including decreased blood-borne infections through injection.
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**Study Source:** Haley, D. F., et al. (2026). Cannabis legalization and cannabis and opioid use in a large, multistate sample of people who inject drugs: A staggered adoption difference-in-differences analysis. *Drug and Alcohol Dependence*. DOI: 10.1016/j.drugalcdep.2026.113040.
