Have California’s medical marijuana dispensaries helped ease the state’s opioid crisis? Several studies have found lower rates of opioid-related overdoses in states that have legalized marijuana for medical purposes.

Now, a new study published in the Journal of Health Economics suggests states that have made it easiest for patients to buy medical marijuana -- primarily via dispensaries -- have seen the greatest impact on opioid overdose deaths. The study was co-authored by researchers from UC Irvine and the RAND Corporation.

"Dispensaries need to be open and operating to see the effect,” the RAND Corporation’s Rosalie Pacula, one of the study’s authors, said at a recent conference sponsored by UC Irvine’s new Center for the Study of Cannabis. “Market size matters.”

Still, Pacula cautioned that changing state marijuana laws and the evolving nature of the opioid crisis make it difficult to formulate solid conclusions. Plus, she said, the long-term health impacts of using marijuana -- especially today’s potent and varied derivatives -- are unknown.

"We need more information and longer time periods in order to see what the longer term effects are,” she said.

A 2017 report from the National Academies of Sciences, Engineering, and Medicine confirmed marijuana’s usefulness in reducing pain. And many patients have reported needing fewer prescription painkillers after starting on medical marijuana.

Still, experts said cannabis won’t solve the opioid crisis.

“Is it going to be a cure? I don’t think so,” Igor Grant, director of UC San Diego's Center for Medicinal Cannabis Research, said.

For one thing, only some opioid addicts use the drug for pain; many use it to get high.

Keith Humphreys, who studies addiction and drug policy at Stanford University, agreed.

“Many people use opioids and cannabis and one doesn’t necessarily make them stop the other,” he said.

But Humphreys said we need more granular research.

"The only way to figure out whether it works is to study individuals, not states.”

It’s extremely difficult to study cannabis in the U.S. because of federal restrictions. And until recently, the government only allowed researchers to use cannabis grown at the University of Mississippi.

Humphreys and Grant said they were hopeful about the potential for more and better research in the near future.

California’s new recreational marijuana laws include a commitment to give state universities $2 million annually for medical cannabis research.

“It’s sort of a fertile time,” Humphreys said. “If we can get the regulatory environment right such that people can do the science without it being incredibly cumbersome and incredibly expensive, it’s potentially quite exciting."