DENVER -- Colorado's tourists aren't just buying weed now that it's legal - they're ending up in emergency rooms at rates far higher than residents, according to a new study.

Doctors reviewed marijuana-related emergency-room admissions at a hospital near Denver International Airport during 2014, when the sale of recreational pot became legal. The results will be published Thursday in the New England Journal of Medicine.

The physicians found that the rate of emergency-room visits possibly related to marijuana doubled among out-of-state residents in the first year of recreational pot sales. The rate went from 85 per 10,000 visits in 2013 to 168 per 10,000 visits in 2014.

Among Colorado residents, the rate of emergency-room visits possibly related to cannabis use did not change significantly between 2013 and 2014. Among Colorado resident emergency-room patients, 106 per 10,000 visits complained of marijuana-related ailments in 2013 and 112 per 10,000 visits complained of marijuana-related ailments in 2014.

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The difference between tourists and residents played out statewide.

Doctors in the study compared the hospital rates to data from the Colorado Hospital Association. That showed the rate among out-of-state residents rose from 78 per 10,000 visits in 2012 to 112 per 10,000 visits in 2013 to 163 per 10,000 visits in 2014. Among Colorado residents, the rate of emergency-room visits possibly related to cannabis use increased from 61 to 70 to 86 to 101, respectively.

Tourists and Coloradans also had different complaints related to marijuana. Coloradans across the time period mostly complained of gastrointestinal problems, while the most common ailment by visitors was psychiatric, including aggressive behavior and hallucinations.

Men were more two to three times more likely than women among both groups to complain of cannabis-related ailments in emergency rooms. Coloradans were slightly younger than out-of-state residents, with a median age of 34 for residents and a median age of 35.5 for visitors.

The doctors said the difference between tourists and residents caught them by surprise.

"We didn't expect people from out of state to actually be coming to the emergency department mentioning this drug more often," said Dr. Andrew Monte, a toxicologist and emergency-room physician at the University of Colorado Hospital in Aurora.

The cases of both tourists and residents reporting feeling like they'd overdosed on pot were a "vast minority" of those showing up complaining of a cannabis-related ailment, Monte said. Instead, the patients usually reported that pot exacerbated an underlying medical condition, especially schizophrenia or psychosis.

The study included all cases where patients mentioned cannabis. Monte said the increase has two likely explanations: more people using pot, and more patients fessing up about using pot to doctors because it's legal.

"There's more communication between patients and providers, and of course there's just more marijuana out in the community," Monte said. "People can come in and say, 'Hey, I've got chest pains and I used marijuana a week ago.' Now, that's got nothing to do with the marijuana."

None of the cases in Monte's study were fatal.

The effect of marijuana legalization on Colorado tourism is a matter of some dispute.

Colorado set records in 2014 for overall visitors (71.3 million) and tourist spending ($18.6 billion). But Colorado had also set records in the previous three years, when pot sales were restricted to state residents with medical ailments. (Tourist numbers for 2015 aren't yet available.)

The Colorado Tourism Office did report in a 2015 visitor survey that the marijuana laws influenced vacation decisions nearly 49 percent of the time.

State health officials say they're trying to educate tourists about responsible pot usage through educational pamphlets and signs at pot shops, a big part of a $5.7 million "Good To Know" campaign launched last year.

But health authorities add that Colorado can't advertise about how to use pot in other states, and that travelers likely use marijuana differently than people staying home.

"You're more likely to overdo it on vacation, with marijuana just like with anything else," said Mike Van Dyke, branch chief for environmental epidemiology at the Colorado Department of Public Health and Environment. "You have that vacation mentality. You're there to have a good time."