The Impact of Medical Marijuana Legalization on Opioid Prescriptions

Since the late 1990s, opioids have been increasingly prescribed for pain treatment in the U.S as a result of aggressive marketing by pharmaceutical companies. This has resulted in more than 450,000 opioid overdose deaths since then. In the same time period, several U.S. states have legalized medical marijuana, a drug that can also be used for pain relief. As a result, medical marijuana can be used as a substitute for opioids, leading to a reduction in opioid prescriptions. On the other hand, marijuana use can lead to increased substance abuse, leading to a potential increase in opioid prescriptions. The lack of scientific and medical knowledge along with the uncertain regulatory environment vis-a-vis medical marijuana use also makes it possible that its legalization has no impact on opioid prescriptions. With claims data from a large health insurance company in the U.S. between 2006 and 2016, we study the effect of medical marijuana legalization on opioid prescriptions, leveraging the temporal variation in state-wise legalization. We find that, on average, opioid prescriptions decreased after medical marijuana legalization for all three outcome metrics that we consider (number of prescriptions, total days of supply, and total dosage in MME). We also find that the role of physicians in reducing opioid prescriptions after legalization is more prominent than their corresponding role in increasing opioid prescriptions