According to new research published in the New England Journal of Medicine, emergency department visits related to cannabis use appear to be increasing more rapidly among out-of-state residents than among Colorado residents.

“We noticed an increasing number of patients coming to the ER who seemed to be from out of town and we decided to look at the data to see if that was the case,” Dr Howard Kim, of the Northwestern University Feinberg School of Medicine in Chicago, told Reuters.

As a result, scientists conducted a cross-sectional study at University of Colorado School of Medicine in Aurora, that has approximately 100,000 ED visits per year and compared the rates of ED visits with International Classification of Diseases, Ninth Revision (ICD-9), codes of cannabis use between out-of-state residents and Colorado residents from 2012 through 2014.

According to the NEJM study, the rate of ED visits possibly related to cannabis use among out-of-state residents doubled from 85 per 10,000 visits in 2013 to 168 per 10,000 visits in 2014 — the first year of retail marijuana sales. However, among Colorado residents, the rate of ED visits possibly related to cannabis use did not change significantly between 2013 and 2014 (106 per 10,000 visits in 2013 and 112 per 10,000 visits in 2014).

The results suggest that marijuana dispensaries need to do a better job of educating people buying their product, Kim told Reuters.

“I would say visitors to states with legal marijuana should be aware of side effects of legal marijuana use,” said Kim. “If they decide to use, they should do it safely and in moderation.”

In states considering marijuana legalization, he said, policymakers should think of campaigns to educate the public and anticipate this as an issue.