Arizona dispensary lottery shows medical marijuana access increased cannabis ER visits by 45% | Research

The takeaway

Using a natural experiment from Arizona's dispensary lottery, researchers found that zip codes assigned a dispensary saw cannabis-related ER visits increase by approximately 45% over four years.

Cannabis policy researchers, public health planners, healthcare administrators

~45% increase in cannabis ER visits in dispensary zip codes over 4 years

What the researchers found

Zip codes winning a dispensary license saw cannabis-related ER visits increase approximately 45% relative to non-winning zip codes over four years. Weak evidence of increased opioid-related visits was also found. The lottery design provides unusually strong causal evidence for the effect of dispensary access.

Why it matters

The lottery design approximates a randomized experiment, providing stronger causal evidence than typical dispensary studies about the health effects of expanding medical marijuana access.

The numbers in context

Approximately 45% increase in cannabis ER visits in winning zip codes vs. non-winning over 4 years. 36 winning vs. 48 losing zip codes across 69 contested areas. Likely underestimates due to spillover effects.

How the study worked

Natural experiment using Arizona's August 2012 lottery for medical marijuana dispensary licenses. 36 winning zip codes compared to 48 losing zip codes using propensity score weighting. ER discharge data from 2010-2016 for cannabis, opioid, alcohol, and cocaine-related visits.

What this study cannot tell us

ER discharge data may not capture all cannabis-related presentations; spillover between neighboring zip codes likely attenuates the measured effect; cannot distinguish between more use vs. more acute reactions; Arizona-specific context.

How to read the evidence

Strong quasi-experimental design using randomized lottery allocation, though limited by ecological data and spillover concerns.

When this study was published

Published in 2020.

The bigger picture

While dispensary access aims to provide safe, regulated cannabis, increased ER utilization suggests that expanded access also brings health system costs that policymakers should anticipate.

Questions still open

Are the ER visits driven by new users, higher-potency products, or edible miscalculations? Do the ER visits represent serious harm or mostly precautionary visits?

Common questions

Why is this study particularly credible?

Arizona allocated dispensary licenses by lottery, creating a natural experiment where some zip codes randomly got dispensaries and others did not. This randomization mimics a controlled experiment and reduces the bias that affects most dispensary studies.

Does this mean dispensaries are harmful?

The study shows dispensary access increased ER visits for acute cannabis causes. Whether these visits represent serious harm or precautionary presentations (like anxiety episodes) is not addressed. The finding suggests expanded access has health system impacts that should be planned for.

Read the original research

A lottery test of the effect of dispensaries on emergency room visits in Arizona.

Health economics, 29(8), 854-864

View on PubMed ↗Publisher’s paper ↗

Citation

Conyers, Gregory; Ayres, Ian. (2020). A lottery test of the effect of dispensaries on emergency room visits in Arizona.. Health economics, 29(8), 854-864. https://doi.org/10.1002/hec.4013