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Legal marijuana either eases opioid crisis or makes it worse. The evidence is split.

About a third of Americans live in a state that allows recreational marijuana.

As more states legalized marijuana for recreational or medical use, hopes were raised that wider availability of legal cannabis would help ease the opioid overdose epidemic, but some of the latest findings do not provide definitive answers, experts say.

Some thought cannabis could offer an alternative to opioids for treating chronic pain and therefore reduce opioid overdoses and deaths. Others believed cannabis also might help people with opioid use disorder to curb the addiction.

But research over the years has yielded mixed results, according to the experts.

A study published this week in Health Economics found that the implementation of recreational marijuana laws in 2017 was associated with a decline in opioid-related emergency department visits — but that decline did not persist after six months.

Researchers observed this trend after studying data from 29 states, including four — California, Maine, Massachusetts and Nevada — that implemented the laws in 2017. Those four states saw a 7.6 percent reduction in opioid-related emergency department visits for six months after the laws went into effect.

The researchers concluded that while recreational cannabis laws may offer some help in fighting the opioid crisis, they are “likely not a panacea.” They noted that about a third of Americans now live in a state with a recreational cannabis law. Yet during the pandemic, overdose deaths from opioid use rose by more than a third to 69,000 in 2020, according to provisional data released this week by the Centers for Disease Control and Prevention. Drug overdose deaths overall reached a record 93,000 last year.

Study author Coleman Drake, an assistant professor of health policy and management at the University of Pittsburgh, said some people may have turned to marijuana instead of opioids for pain relief, at least initially. Others may have tried to use marijuana to wean off of opioids but found it didn’t work.

“Maybe for those who already have opioid use disorder, they're finding that cannabis is not sufficient to treat all the symptoms of their condition,” he said, and at that point they may turn to heroin, fentanyl or other opioids. “There might be a substitution back towards that after a period of time,” he said.

But in a study published in January in the British Medical Journal, researchers found that the availability of legal marijuana dispensaries in one U.S. county was associated with a decrease in opioid-related deaths. An increase from one to two dispensaries in one county, for instance, was linked with a 17 percent reduction in deaths. The study looked at 812 counties in 23 states and Washington, D.C., that allowed cannabis dispensaries to operate by the end of 2017.

Our study provides further evidence that marijuana use is not effective in reducing nonmedical opioid use.

Study author Balázs Kovács, an associate professor of organizational behavior at Yale University, said the findings do not prove a causal relationship but do suggest an association.

“I would say there is some role of the cannabis dispensaries,” he said, possibly to increase access to marijuana for treating pain or to help people already on opioids to cut back.

Does marijuana promote or replace opioids?

Yet another study published last year in the journal Addiction found that marijuana use seemed to promote — rather than replace — opioid use. Researchers followed more than 200 adults in New York who used nonmedical or illegal opioids. Over 90 days of study, the researchers found that on the days when people used marijuana, the odds of them using nonmedical opioids almost doubled, regardless of whether they were experiencing pain.

“Our study provides further evidence that marijuana use is not effective in reducing nonmedical opioid use,” said study author Dr. Mark Olfson, a professor of psychiatry and epidemiology at Columbia University.

Olfson told NBC News via email that it’s hard to reach solid conclusions from reports linking fewer opioid-related deaths or less opioid prescribing to the passage of recreational and medical marijuana laws.

“It is often the case that drawing inferences about the behavior of individuals from aggregated data can be misleading,” he said. “In my view, it is unfortunate that these findings continue to receive attention as supporting a role for marijuana in the treatment of opioid use disorder.”

Other doctors also are skeptical that marijuana is a cure for opioid addiction. The American Society of Addiction Medicineadopted a policy statement in October declaring “there is no current evidence that cannabis is effective for the treatment of OUD (opioid use disorder).”

There are, however, Food and Drug Administration-approved medications for treating opioid addiction — buprenorphine, methadone and naltrexone — and those are considered the treatments of choice, said Dr. Andrew Saxon, a professor of psychiatry and behavioral sciences at the University of Washington School of Medicine and a member of the American Psychiatric Association’s council on addiction psychiatry.

“They are available, they are very effective and that’s what people should be looking for, not trying to use cannabis to help them with their problems with opioids,” he said.

CBD can reduce opioid cravings

Saxon said cannabis use is very common among his patients with opioid addiction, and it doesn’t seem to be helping them curb opioid use. “If we thought that cannabis could help people with opioid use disorder, the ones who were using cannabis should be doing better than the ones who were not using cannabis,” he said.

He noted that one specific cannabis compound, cannabidiol (CBD), does show some early promise for reducing opioid cravings. But he said CBD has been largely bred out of most marijuana sold for recreational use, in favor of higher levels of the intoxicating tetrahydrocannabinol (THC) compound. CBD does not cause intoxication.

One of the researchers studying pure CBD is Yasmin Hurd, director of the Mount Sinai Addiction Institute in New York. She and her colleagues published research in the American Journal of Psychiatry in 2019 showing that CBD can reduce cravings and anxiety in people with a history of heroin addiction who were not currently using the drug. “Those are the things that usually trigger relapse in people,” she said.

But while the CBD findings are promising, Hurd said, more research is needed. And she emphasized that not all marijuana products are alike, so people shouldn’t generalize that any form of cannabis potentially could help. Marijuana also is intoxicating and can lead to dependence, and there are “scary” reports of marijuana on the streets being laced with fentanyl, she warned.

Opioid overdoses accelerated during the Covid-19 pandemic, and Hurd recommended that anyone struggling with opioid addiction seek professional help rather than experimenting on their own with marijuana or stopping doctor-recommended treatment that could be lifesaving.

“It's important that they talk to their doctors and not just switch out” of a proven treatment for an unproven one, she said. “There really needs to be a partnership with their physician.”