Six days before Prince died, the iconic pop star was hospitalized after possibly overdosing on Percocet. His death on April 21 involved overdosing on another painkiller, fentanyl. Both are among the prescription opioids that alleviate the pain of millions of Americans every year—often at the price of their needing ever greater amounts and the risk of overdose. The U.S. “is in the midst of an unprecedented opioid epidemic,” according to the Department of Health and Human Services. Prescription opioid overdoses killed more than 165,000 Americans between 1999 and 2014, and the health and social costs of abusing such drugs are estimated to be as much as $55 billion a year. The problem has led experts to scramble for a less dangerous alternative for pain relief—and some research points to medical marijuana.

As early as 15 years ago physicians began hearing that patients were using cannabis instead of prescription opioids for pain. These anecdotes inspired a research team led by Marcus Bachhuber, assistant professor of medicine at the Montefiore Medical Center in New York City, to examine whether some states’ legalization of medical cannabis had affected the number of opioid overdose deaths. Published in 2014, the study revealed an intriguing trend: between 1999 and 2010, states that permitted medical marijuana had an average of almost 25 percent fewer opioid overdose deaths each year than states where cannabis remained illegal.

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