Tourists who come to Colorado and take advantage of the state's liberal marijuana laws often end up in emergency rooms, doctors said Wednesday.
Emergency department visits involving marijuana-using visitors doubled from 2013 to 2014, the first year cannabis use was legalized in Colorado, a team of Denver-area doctors said.
"At our institution, 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, which was the first year of retail marijuana sales," wrote Dr. Andrew Monte, an emergency room toxicologist at the University of Colorado Denver in a letter to the New England Journal of Medicine, along with colleagues.
Rates of visits involving marijuana did not change for in-state Colorado residents, they found.
Monte said some of the cases may simply involve people who mention marijuana use to the ER staff when they're in the hospital for something else. But even accounting for that, rates are up, he said.
"We see three different groups of people that come into the department," Monte told NBC News. "The first are exacerbations of underlying medical conditions."
These could include patients with anxiety disorders or schizophrenia, which can be worsened by marijuana use, or people with heart disease who can develop complications with heavy use, Monte said.
That's not always dangerous but it could be, he said. "In a young health person with a young healthy heart, absolutely not," he said. But in people with underlying heart disease, the stress of a racing heart from eating marijuana could be fatal, Monte said.
A second group would be directly affected by the drug. "These would be things like motor vehicle collisions when they are high or smoking," Monte said. Cyclic vomiting, which can come with heavy daily use, is another issue, Monte said.
The third group are people who smoke or eat a little too much pot and get heavily intoxicated and scared.
"Those are disproportionately due to the edibles," Monte said.
"I took care of a guy just the other night that had come in, was flying out of town, had come in to see friends, decided to drink some liquid just before going to the airport. He started to feel anxious. His heart started to race. So he came into the emergency department. So we made sure he had no heart trouble, checked the blood sugar, gave him a little bit of sedative and then sent him on to the airport."
States planning to legalize marijuana should take heed of these experiences and start education campaigns before the laws loosen up, Monte said.
"People should start low and go slow and have a full understanding of what the risks are," he said. "Nothing is 100 percent safe. You can get intoxicated by water if you drink too much of it."
Marijuana use has more than doubled in the U.S. since the beginning of the century. Legal U.S. pot sales hit a new high of $5.4 billion in 2015. Colorado sales surpassed $100 million last year for the first time. About 9.5 percent of U.S. adults used marijuana in 2013, up from 4.1 percent in 2001-2002.
But with more sales come more problems for users. Researchers found that nearly three of 10 marijuana users manifested a marijuana use disorder in 2012-2013. Studies suggest that using marijuana and alcohol together impairs driving more than either substance alone and that alcohol use may increase the absorption of THC, the psychoactive chemical found in marijuana.