One of the benefits of cannabis decriminalization in the United States is the ability to conduct research on the drug’s benefits and harms. A breakthrough study involving the impact of cannabis legalization on the use of opioids would not have been possible without a history of state cannabis legalization.

The study, just published in the journal Drug and Alcohol Dependence, involves 28,069 “people who inject drugs” (PWID) from 13 states. Four datasets were provided by the Centers for Disease Control’s (CDC’s) national HIV behavioral surveillance surveys conducted in 2012, 2015, 2018, and 2021.

The demographics of the sampled population are nowhere near average for the U.S. For example, 78% lived at or below the federal poverty line, and nearly two-thirds (64%) had experienced homelessness during the past 12 months. The racial mix was 41% Black, 39% White, and 19% Hispanic/Latinx.

The researchers compared the information with the dates of marijuana liberalization in the 13 states examined and found these two fascinating conclusions:

• “We found no evidence of an overall association between cannabis legalization and daily cannabis use.”

• “We found an inverse association between [medical + recreational use] compared to [medical use] only and daily opioid use.”

First, neither the legalization of medical marijuana nor the legalization of recreational marijuana led to an increase in cannabis use among PWID. Secondly, they did lead to a reduction in daily opioid use, leading the researchers to conclude:

PWID in states with recreational cannabis laws were less likely to use opioids daily.

And:

Cannabis legalization may potentially reduce opioid-related harms.

This isn’t the only recent research pointing to THC as a therapeutic in the treatment of opioid use disorder. A study in the journal Pain Management last August found that people treated with opioids for back pain used less opioids when also prescribed a THC drug. Median opioid use for the 56 patients who completed the study plummeted from 40mg/day to 2.7mg/day.

A 2021 study in the journal Pain Physician similarly found a “dramatic reduction in opioid use” among patients with chronic pain who were prescribed a cannabis painkiller. In this case, of the 85 people who completed the six-month trial, there was a 67.1% average reduction in use, and six months later, that number had risen to 73.3% reduction.

Both the Pain Management and Pain Physician studies have small sample sizes showing big results. The new Drug and Alcohol Dependence study has a huge sample size and still shows significant and encouraging results for the use of THC products as opioid substitutes.

Written by Steve O’Keefe. First published February 3, 2026.

Sources:

“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, January 23, 2026.

“Opioid reduction in patients with chronic non-cancer pain undergoing treatment with medicinal cannabis,” Pain Management, August 11, 2025.

“Medical Cannabis Used as an Alternative Treatment for Chronic Pain Demonstrates Reduction in Chronic Opioid Use — A Prospective Study,” Pain Physician, January/February 2022.

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