Can medical cannabis help to fight the opioid epidemic? Many believe that it can. But a new study finds that people who use medical marijuana actually have higher rates of medical and non-medical prescription drug use — including pain relievers.

Rather than being at lower risk, people who use medical cannabis may be at higher risk for non-medical prescription drug use. Though, a supplementary commentary questions whether medical cannabis is the cause of higher prescription drug use, or whether other factors explain the association.

People who used medical cannabis were more likely to say they had used prescription drugs in the past year. They were about 60 percent more likely to report any prescription drug use, relative to those who did not use medical cannabis.

People who used medical cannabis were also more than twice as likely to report non-medical use of prescription drugs, as well as pain relievers, stimulants, and tranquilizers. Non-medical use of pain relievers is of specific interest because of pain relievers’ role in the opioid overdose epidemic.

Upper levels of non-medical prescription drug use by people who used medical cannabis persisted in an examination limited to people who used prescription drugs. This suggests that the elevated risk for prescription drug non-medical use among people who use medical cannabis cannot be ascribed simply to their having a medical concern or greater access to prescription drugs.

Previous studies have reported that states where medical cannabis is legal have lower rates of medical and non-medical prescription drug use and related harms — including opioid overdose. These reports have led many to believe that use of medical cannabis is a protective factor against non-medical prescription drug use. Though, individual-level inferences cannot be made using the ecological studies cited frequently in the debate over medical cannabis.

In other studies, people who take medical cannabis consistently report replacing cannabis for other prescription and illegal drugs. To fully comprehend the effect of medical marijuana on the use of other drugs, prospective longitudinal studies randomizing patients to marijuana versus other treatments are urgently needed.