The head of the National Institute on Drug Abuse said there’s no evidence that marijuana weans people from opioid addiction – and promoting such treatment might deny people a chance at recovery.

The nation's research agency on drug use wants to assess cannabis ingredients as possible treatments for more than 2 million Americans with opioid-use disorder, NIDA Director Nora Volkow said this week. But there's not any evidence that marijuana works for opioid addiction, she said.

New York, New Jersey, Pennsylvania and Illinois allow marijuana as a treatment for addiction to opioids such as heroin, fentanyl and OxyContin. The Maryland General Assembly is considering a bill that would add opioid-use disorder to the state's list of qualifying medical conditions for marijuana.

Volkow said she worries people who substitute marijuana for the Food and Drug Administration-approved medications buprenorphine, methadone and naltrexone might be more likely to relapse.

"If you don’t treat it properly, your risk of dying is quite high," Volkow told the USA TODAY Editorial Board in a wide-ranging interview. "My main concern is by basically misinforming potential patients about the supposedly beneficial effects of cannabis, they may forgo a treatment that is lifesaving."

NIDA has two or three studies planned or underway to evaluate cannabis ingredients for opioid addiction. Still, Volkow said, scientific evidence does not support claims that marijuana helps people kick opioids. 

"I’m not saying it’s not possible," Volkow said. "Like anything else, we do science in order to determine and provide the evidence of whether it’s effective or not."

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