Medical marijuana’s growing acceptance in the U.S. is prompted mostly by evidence showing effectiveness in treating cancer and neurodegenerative diseases, among others. Pain, on the other hand, has always been a point of contention between regulators, doctors, and patients, mostly because of its vague nature — you can’t really pinpoint the severity of a person’s pain, and some people may just be looking to get high. Though this has led some doctors to be apprehensive about prescribing marijuana for pain, a new study may offer a reason to welcome marijuana as a pain treatment.

The study, published in JAMA Internal Medicine, found that states that implemented medical marijuana laws saw a reduction in average opioid analgesic overdoses and deaths, both from prescription painkillers and illicit drugs like heroin. Their study went as far back as 1999, when only three states had legalized medical marijuana. In all, states with medical marijuana laws had a 24.8 percent lower average of annual overdose death rates when compared to states that hadn’t legalized the drug.

What’s even better, the rates of overdose deaths decreased over time, presumably as medical marijuana became more widely used. Whereas the first year of legalization saw an average decrease in deaths of about 20 percent, there was an average reduction of 33.3 percent after six years. By 2010, which was the end of the study period, there were about 1,729 fewer deaths from opioids, the study found.

“Approximately 60 percent of all opioid analgesic overdose deaths occur among patients who have legitimate prescriptions from a single provider,” the researchers wrote. “This group may be sensitive to medical cannabis laws; patients with chronic non-cancer pain who would have otherwise initiated opioid analgesics may choose medical cannabis instead.”

Though pain can arise from cancer, heart disease, diabetes, arthritis, and many other conditions, it can linger long after the disease has subsided. In all, chronic pain affects an estimated 100 million Americans, according to the American Academy of Pain Medicine, far more than any rates of pain from the other aforementioned diseases.

Marijuana, and specifically some of its cannabinoids, have long been considered to play a role in pain relief. In one study from San Francisco General Hospital, 34 percent of HIV patients who used marijuana for pain experienced a reduction in symptoms compared to only 17 percent of a control group. Another more novel experiment used capsaicin, an ingredient in chili peppers, to induce pain on patients’ arms. When they gave the patients marijuana, those who took higher doses reported less burning.

Marijuana has been shown effective in reducing opioid use through other studies as well. A study from the University of California, San Francisco, found that patients given medical marijuana as a supplement to an opiate regimen reported less pain than when they used opiates alone. Perhaps the best part about the treatment, however, was that patients could theoretically reduce their opiate doses “for longer periods of time if taken in conjunction with cannabis,” lead author Dr. Donald Abrams said in a press release.

For the current study, Pennsylvania researchers looked at data regarding annual opioid overdose deaths in the country from 1999, when three states had implemented marijuana laws, to 2010, when an additional 10 states had implemented laws. They stopped short of saying that the cause of these reductions was from patients switching to cannabis. However, in a hopeful tone, they noted that “if medical cannabis laws lead to decreases in polypharmacy,” or the use of multiple medications to treat one condition, “in people taking opioid analgesics, over dose risk would be decreased.” According to the Centers for Disease Control and Prevention, 46 people die each day from prescription painkiller overdoses.

Source: Bachhuber M, Saloner B, Cunningham C, Barry C. Medical Cannabis Laws and Opioid Analgesic Overdose: Mortality in the United States, 1999-2010. JAMA Internal Medicine. 2014.