A synthetic control analysis of Colorado, Washington, and Oregon found a consistent negative relationship between recreational marijuana dispensary openings and opioid death rates, but the effect did not reach statistical significance in any state.
Policymakers, researchers, and anyone interested in whether cannabis legalization affects the opioid crisis.
Consistent negative trend in opioid deaths across all 3 states, but none reached statistical significance
What the researchers found
The average treatment effect was approximately -6.49 opioid deaths per capita for Colorado, -2.89 for Washington, and -4.8 for Oregon after recreational dispensaries opened. However, none of these reductions reached statistical significance. Robustness checks confirmed the consistent negative direction but continued non-significance.
Why it matters
The opioid epidemic remains a major public health crisis. Whether legal cannabis access reduces opioid deaths is a high-stakes policy question. This study finds a suggestive but inconclusive downward trend, adding nuance to claims on both sides of the debate.
The numbers in context
Average treatment effects: Colorado -6.49, Washington -2.89, Oregon -4.8 opioid deaths per capita. All were non-significant. The consistent negative direction across all three states and robustness checks suggests a possible real effect that the study lacked power to confirm.
How the study worked
Researchers used the synthetic control method to construct counterfactual versions of Colorado, Washington, and Oregon using state-level data from the CDC, Bureau of Labor Statistics, US Census Bureau, and other sources. These three states were chosen because they were the first to legalize recreational marijuana, providing the longest post-treatment observation periods.
What this study cannot tell us
Synthetic control method relies on finding good donor states, which may be imperfect. Only three states were analyzed. Opioid death rates are influenced by many concurrent policy changes (naloxone access, prescribing guidelines, fentanyl emergence) that complicate attribution. The post-treatment period may not be long enough to capture delayed effects.
How to read the evidence
Rigorous synthetic control design analyzing the three states with the longest legalization history, but limited by non-significant findings and only three observations.
When this study was published
Published in 2025.
The bigger picture
The consistent direction of effect across three independent state analyses is notable even though no individual result was significant. This pattern is common in policy research where effects are real but modest relative to the noise in state-level data. The findings neither confirm nor refute the hypothesis that cannabis access reduces opioid deaths.
Questions still open
- Would analyzing more states that have since legalized recreational cannabis produce significant results? Is the effect too small to detect with state-level data, but real at the individual level? Does the type of cannabis available (high-THC flower vs. CBD products) matter for opioid substitution?
Common questions
Did cannabis legalization reduce opioid deaths?
Why only three states?
Read the original research
Recreational marijuana legalization's impact and opioid death rates: A synthetic control approach.
Public health, 239, 201-206
Citation
Denkyirah, Elisha Kwaku; March, Raymond J; Furton, Glenn L; Rayamajhee, Veeshan; Yonk, Ryan M. (2025). Recreational marijuana legalization's impact and opioid death rates: A synthetic control approach.. Public health, 239, 201-206. https://doi.org/10.1016/j.puhe.2024.12.047