A new study documented a sharp rise in emergency-room visits linked with marijuana following legalization in Colorado.

One of the key drivers of the ER visits was a mysterious syndrome characterized by severe nausea and repeated vomiting.

Little is known about the condition, called cannabinoid hyperemesis syndrome, or CHS.

The only known way to cure CHS is to stop using marijuana. Researchers still aren't sure what causes it.

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When she became so uncontrollably sick that she resorted to scalding her skin in a hot bath for the third time in a row, Mrs. X began to wonder whether it had something to do with smoking marijuana.

For nearly a decade, the Australian woman had experienced sudden and severe episodes of nausea and vomiting in connection with using the drug. Before that, she'd smoked safely for years, with no symptoms.

In 2004, a team of emergency-room physicians in Australia detailed her experience anonymously alongside a handful of similar cases in the same region that year. In nearly all those cases, the people described an illness that cropped up suddenly, often after decades of normal marijuana use. Piping hot baths were their only relief.

The Australian physicians dubbed it "cannabinoid hyperemesis syndrome," or CHS.

Though the Australians' report raised some red flags locally, most experts continued to think that cases like Mrs. X's were rare across the globe — until a spate of similar reports cropped up elsewhere.

Now, several recent studies from ER physicians across Europe and the US are suggesting that CHS could be a lot more common than previously thought.

The latest study was published on Monday by a team of clinicians in Colorado, where marijuana was legalized medically in 2009 and recreationally in 2014. In their study, which appeared in the journal Annals of Internal Medicine, the physicians described more than 2,500 cannabis-related ER visits to a large public hospital in the state from 2012 to 2016.

They found that stomach issues like nausea and vomiting were the main driver of the trips, even before psychiatric problems like intoxication and paranoia. And of those stomach issues, CHS was the most commonly reported problem and the top reason for the people to be booked at the hospital.

"To see that this was a leading reason for people coming to the ER, that was pretty striking," Andrew Monte, an associate professor of emergency medicine at UCHealth University of Colorado Hospital who led the study, told Business Insider.

"We have to do a better job of educating users on the fact that this phenomenon exists," he added.

Nora Volkow, the director of the National Institute on Drug Abuse, echoed Monte's concerns about cannabis and CHS in an editorial published with the study.

"We must recognize that the full range of potential adverse health consequences from cannabis consumption are not fully understood," she wrote.

From a 'barely known' illness to something that could affect millions each year

Because marijuana was widely illegal until recently, few studies have explored its effects, positive or negative. Hollis Johnson/Business Insider

Because cannabis was widely illegal until very recently, very few studies have explored the full range of its effects, positive or negative.

Two decades ago, CHS was unheard of. Then in the early 2000s, a spate of researchers began to describe clusters of stomach-related issues that appeared to stem from heavy and repeated cannabis use. Though they coined a name for the problem, they still had no idea what was causing it or how to stop it.

More than a decade later, in 2017, a team of German ER doctors described CHS as a "barely known" illness characterized by intense nausea, vomiting, and stomach pain. They still hadn't pinned down a cause, but they did identify a cure: quitting cannabis.

A year later, in New York, clinicians surveyed thousands of patients at a large urban public hospital and concluded that every year as many as 2 million Americans could experience something like CHS. Again, the only definitive treatment they identified was quitting marijuana.

Read more: A mysterious syndrome in which marijuana users get violently ill is starting to worry researchers

For the latest study, the Colorado researchers chronicled nearly 10,000 ER visits to the University of Colorado Health's Anschutz campus, a large public hospital in Aurora, roughly 30 minutes from Denver. Of all the visits, about 2,500 were related to marijuana.

Of the weed-related visits, 31% were stomach-related, making stomach issues the leading cause of all ER trips for cannabis. And of the stomach-related cannabis visits, CHS emerged as the most common adverse event and the main driver of hospital admissions.

Monte's findings are chipping away at the assumption that CHS is uncommon.

"CHS is certainly not very rare," Monte told Business Insider. "We see it absolutely every week in our ER."

Other researchers agree.

"This isn't surprising, and we're certainly going to see more of this," Joseph Habboushe, an associate professor at NYU Langone and the lead author of the CHS paper published last year, told Business Insider.

Habboushe is working on a study to identify some new relief methods for the symptoms of CHS. Monte said one of his graduate students was working on a similar paper.

For Mrs. X, the only thing that helped was quitting. When she started smoking again, she was OK for a few months, but then her symptoms returned.

The authors of the Australian study documenting her case wrote in 2004 that the people who "rechallenged themselves by resuming marijuana" had "relapsed within months."