Medical Marijuana Laws, Marijuana Use, and Annual Opioid Analgesic Sales in the United States

Aim: To date, 23 states have enacted some type of medical marijuana legislation (MML), and more states may soon pass similar laws. It has been hypothesized that MML may reduce opioid overdose deaths. This study assesses whether state MMLs are associated with opiate consumption and whether this association is mediated by state prevalence of past-month marijuana use.  Methods: Annual opioid sales for 2003-2013 were culled from the Automation of Reports and Consolidated Orders System (ARCOS). This data includes annual sales of seven major opiates (e.g., oxycodone) by state. Morphine equivalent doses (MED) per 100,000 residents were calculated for each state-year observation. Mixed models with a random effect for state and a fixed effect for year were used to estimate differences in the (natural log) average MED rate for states with either effective MML, to be implemented MML, or without MML. Results: We found that the prevalence of past-month marijuana use mediated the association between MML and opiate consumption, and that this association was moderated by MML status. For example, for states that have never implemented an MML, a one percent increase in the prevalence of past-month use was associated with a 4.1% increase in opioid consumption (β= 0.041, p-value=0.059). However, for states that passed future laws or states with a current MML in effect, the association between past-month marijuana use and opiate consumption was near or significantly different (β= -0.039, p-value=0.196, β= -0.053, p-value=0.038, respectively) than the association observed for states that had never passed MML. Conclusions: While the prevalence of marijuana use in states that have never passed MML is associated with increased opioid consumption, this did not hold for states that have passed MML. By increasing availability and thus the prevalence of marijuana use, MML may reduce opioid consumption at the state level.