This obscure marijuana-related illness is on the rise in states with legalized pot.

Ever heard of cannabinoid hyperemesis syndrome? Don’t worry, almost no one else has either. But it’s a very real, and frightening, condition that can affect people who smoke heavy amounts of marijuana. And unfortunately, it appears to be on the rise in states that have legalized recreational cannabis.

“It is certainly something that, before legalization, we almost never saw,” Dr. Kennon Heard told CBS News. “Now we are seeing it quite frequently.”

The syndrome manifests itself with intense vomiting and abdominal pain that strangely enough is relieved when the person suffering takes repeated hot showers or baths. Abstaining from marijuana also typically causes the symptoms to completely go away.

“Patients are given IV fluids and medication to resolve the vomiting and help with the pain,” Dr. Heard told CBS. “But the treatment is really to stop using marijuana, or at least to cut back severely, and that’s really the only way to make it better.”

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But because it’s so poorly understood, people showing up to emergency rooms with the symptoms are often misdiagnosed. First discovered 10 years ago in Australia, researchers are still trying to understand exactly how the condition works. In particular, the effect of uncontrolled vomiting is directly at odds with one of marijuana’s most widely accepted health benefits as an antiemetic, i.e. something which stops vomiting and nausea, bringing great relief to individuals suffering from conditions like cancer, Crohn’s Disease and HIV.

However, according to a small collection of reports from hospitals in four states, the number of people showing up to ER’s with cannabinoid hyperemesis syndrome has risen sharply in recent years. One study showed that in two Colorado hospital the admittance rates for the condition have doubled since 2009. Similar increases have been reported in Washington, DC and Maryland where pot was recently legalized.

“These folks are really suffering. They can get pretty sick,” Dr. Eric Lavona of the Denver Health Medical Center said in an interview with the Missoulian. “They vomit like crazy and make frequent emergency department visits because they just can’t stop vomiting.”

Of course, those increased numbers can’t be entirely pinned on increased marijuana use. As CBS notes, many patients suffering from the condition may be reluctant to admit to using marijuana in states where the drug is still illegal.

In the meantime, the reports of CNS show that while recreational and medicinal marijuana are proving to be relatively safe for the vast majority of users, there are still potential risks associated with heavy use and other health conditions. And more importantly, that the science on the full range of effects from cannabis use is still far from settled.