The Association Between Medical Cannabis Laws and Flows of Opioids by Dosage Strength to US Pharmacies – Evidence From Detailed ARCOS Data, 2006–2014

Abstract A growing body of research finds a consistently negative relationship between medical cannabis access and aggregate measures of opioid use. Nothing is currently known about the types of opioids that are being most impacted by cannabis access. Using the Callaway and Sant’Anna (2021) difference-in-differences (DID) estimator for the main analysis and data on all opioid shipments to every United States (US) pharmacy from 2006 to 2014, the authors found no evidence of overall change in the total number of morphine milligram equivalent (MME) units of opioids shipped to pharmacies, following the opening of medical cannabis dispensaries. However, across all opioids, the authors found a reduction in the highest MME dosage strengths (8.8% decrease in 50–89 MME doses and 11.3% decrease in 90+ MME doses). This decrease appears to be driven predominantly by commonly diverted opioids, where the authors found a reduction in the highest MME dosage strengths (12.2% in 50–89 MME doses and 13.8% in 90+ MME doses). Further, the authors see a 6.0% increase in low-to-moderate dose opioids (0–49 MMEs). This is consistent with patients using cannabis concomitantly with opioids in order to achieve a lower opioids dose.