A new study finds that in places where medical marijuana has been legalized, illegal use is higher, and more people are at risk for “cannabis use disorder.”

The study, published in JAMA Psychiatry and reported by Reuters, compiles results from three federal studies conducted between 1991 and 2013. Researchers found that illegal marijuana use and so-called “cannabis use disorder” rose at greater rates in states that had legalized medical marijuana than they did in states that had not.

“Cannabis use disorder” is defined as a condition where cannabis users suffer cravings or withdrawals.

Lead author Deborah Hasin, of Columbia University’s Mailman School of Public Health in New York, told Reuters  that the study couldn’t directly link the increase in use to medical-marijuana legalization, but that changes in the law may have had an effect on users’ attitudes toward cannabis, both from a legal and medical perspective.

“”I think all of these things can contribute to increases, but we can’t pinpoint them for sure because it’s not what the study was designed to address,” she told Reuters.

Previous surveys have found mixed results on the question of teen use increasing or decreasing in the context of legalized marijuana. Hasin said that teenagers are generally less concerned with legality, so researchers focused instead on adults.

To read more on the story, head over to Reuters.com.