The Effects of Recreational Cannabis Laws on Pharmacy- and Hospital-Based Opioid Distribution in the United States

Background: Nine states implemented recreational cannabis laws (RCLs) by the end of 2019, providing millions of U.S. residents with access to recreational cannabis. Cannabis is used as a therapeutic substitute for several prescription medications, including those used to treat chronic pain, insomnia, and mental health conditions. Prior literature found medical cannabis laws (MCLs) affect reductions in opioid dispending. Little is known, however, about the potentially larger effects of RCLs, which make cannabis available to millions more U.S. residents.

Methods: We evaluate the impact of RCLs on the distribution of opioids in the U.S. from 2011-2019. Using state-quarter distribution data from the Drug Enforcement Agency’s ARCOS reports and RCL implementation dates from RAND-USC Schaeffer OPTIC data, we estimate the effect of RCLs on opioid distribution for the 9 most common oral analgesic medications (OAMs) using a difference-in-differences approach. We control for state policy and demographic controls, clustering standard errors by state. We separately examine distribution to pharmacies and hospitals, evaluating RCL effects specific to opioid distribution endpoint.

Results: RCLs are associated with a 25% reduction [95% CI = -50.1 to -0.1 , P = 0.049 ] in pharmacy codeine distribution, a 12% reduction [95% CI = -22.5 to -2.7, P = 0.014] in pharmacy hydromorphone distribution, and a 9% reduction [95% CI = -16.9 to -1.7 , P = 0.018] in pharmacy morphine distribution. These estimates are robust to pre-trends tests and exclusion of states without MCLs.

Conclusion: Our findings suggest that, like MCLs, RCLs affect substitution from prescription opioids to cannabis. States should consider this substitution behavior, as well as affects on illicit markets, as they consider expanding RCLs.