The patient in bed nine has been here before. Four visits this month, each one the same: hours of retching, a normal abdominal exam, and labs that refuse to explain the misery in front of me. Somewhere earlier in the chart another clinician has written the phrase that follows these patients around, likely drug-seeking, and it is wrong, and it is costing this person years of their life.

Cannabinoid hyperemesis syndrome, or CHS, is one of the clearest examples in medicine of a condition hiding in plain sight. We have the pattern in front of us constantly. We keep reading it wrong.

What CHS actually is

CHS is a syndrome of stereotyped, recurrent vomiting in people who use cannabis frequently and over a long period. Stereotyped means the episodes repeat in the same shape each time: abrupt onset, hours of intractable nausea and vomiting, then a symptom-free stretch until the next cycle arrives. It sits in the same family as cyclic vomiting syndrome, the older label for unexplained recurrent vomiting, and for years the two were blurred together. What separates CHS is the exposure. The vomiting is driven by chronic, heavy cannabis use, and it resolves when that use stops.

For most of its short history CHS was a clinical impression without hard edges. That changed with the Rome V criteria, the 2026 revision of the diagnostic framework for disorders of gut-brain interaction, the conditions where the signaling between gut and brain misfires. Rome V is the first version to define CHS with numbers rather than gestalt. It requires episodic vomiting that resembles cyclic vomiting syndrome, a history of prolonged use of at least a year and heavy use of at least four days a week or fifteen doses a week, and relief of the episodes after sustained cessation, meaning roughly six months off cannabis or three full vomiting cycles without it. Putting quantitative thresholds on the diagnosis matters, because it moves CHS from a label clinicians reach for when they have run out of other ideas to a condition with criteria you can actually test.

Why the diagnosis takes years

Even with criteria, CHS gets missed, and the delay is not trivial. In the survey work behind the Rome V revision, roughly forty percent of patients waited more than four years for the diagnosis. Four years of emergency visits, CT scans, endoscopies, antiemetics that barely touch the symptoms, and the quiet accumulation of suspicion in the medical record. The reasons are structural. Patients rarely volunteer the true extent of their cannabis use, clinicians rarely ask in a way that invites an honest answer, and both sides carry the assumption that cannabis settles the stomach rather than wrecking it. That last belief does real damage, because many patients with CHS are using more cannabis to treat the very nausea it is causing.

The epidemiology, stated honestly

The honest epidemiology is that CHS is uncommon but climbing. The validation survey that accompanied Rome V put global prevalence around 0.6 percent, roughly twelve times the estimate under the previous framework, with United States figures near 0.4 percent. Among people with cyclic vomiting who use cannabis, close to forty percent meet criteria for CHS. Some of that increase is better recognition. Much of it is not. Cannabis use has risen with legalization, and the potency of what people are consuming has climbed sharply, with THC concentrations in modern products far above what was typical a generation ago. Two variables are moving together here, how much people use and how strong it is, and both track with the syndrome. This follows dose and exposure, not the plant by itself.

The hot-shower sign

The most recognizable feature of CHS is also the most misunderstood. Patients discover, usually on their own, that a hot shower or bath blunts the nausea, and they begin bathing compulsively, sometimes for hours, occasionally scalding themselves in the process. In survey data more than nine in ten patients report that hot bathing relieves their symptoms. Clinicians have historically treated this as a curiosity or, worse, as evidence of something psychiatric. It is neither. It is a rational response to unbearable nausea by people who have found the one thing that reliably helps, and it is specific enough that it belongs at the front of the diagnostic interview. When a young person presents with cyclic vomiting and describes living in the shower, the diagnosis is often already made.

What we think is happening, and what we do not

Why any of this occurs is not fully settled, and honesty about that uncertainty is part of taking the condition seriously. The leading explanations center on the endocannabinoid system, the network of receptors that cannabis acts on. Chronic heavy exposure appears to downregulate CB1 receptors, the main target of THC, changing how the system signals over time. TRPV1, a receptor involved in heat and pain sensation and in gut signaling, is another candidate, and its involvement may explain why heat, in the form of a hot shower, provides relief. Disruption of the hypothalamus, the brain region that governs temperature regulation and helps coordinate the stress response, has also been proposed. These are mechanisms supported by receptor studies and physiological reasoning rather than settled fact. What is clear from the pattern is that heavy, sustained cannabinoid exposure changes the system in a way that stopping reverses.

This is harm reduction, not a verdict on cannabis

None of this is an argument against cannabis. I have written before that cannabis is not the villain in this story, and I hold to that. Most people who use cannabis will never develop CHS. The syndrome clusters at the high-frequency, high-potency end of use, which means the useful conversation is about pattern and dose, not prohibition. Turning CHS into a reason to moralize about cannabis does the same thing the drug-seeking label does. It pushes patients away from the honest disclosure that makes the diagnosis possible in the first place. The harm-reduction position is straightforward: the people getting hurt are heavy daily users of potent products, and they deserve accurate information about the risk rather than judgment about the choice.

What the emergency department can and cannot do

In the emergency department our role is narrow, and worth being honest about. We can rule out the dangerous mimics and correct the dehydration and electrolyte losses that come with days of vomiting. We can offer short-term relief. Standard antiemetics, the drugs we reach for first in ordinary vomiting, work poorly in CHS. The agents with better track records are different: capsaicin cream applied to the abdomen, which acts on the same TRPV1 receptor that heat does, alongside dopamine-blocking medications such as haloperidol and, in selected cases, benzodiazepines. A hot shower, where one is available, remains among the more reliable interventions we can provide in the moment. What the ED cannot do is fix the syndrome. We can end an episode. We cannot end the cycle. Every visit that stops at symptom control and skips the actual diagnosis is a missed opportunity dressed up as a discharge.

What actually ends it

What resolves CHS is cessation, and there is no way to make that sentence easier than it is. Stopping cannabis works. The vomiting cycles fade over weeks to months once use genuinely stops, which is why Rome V builds a six-month abstinence window into the definition. The difficulty is that stopping is hard, and the data are sober about it. In survey work only about one in five patients manages even four weeks of abstinence. Dependence is real, the withdrawal is unpleasant, and many patients are leaning on cannabis to manage anxiety and depression that do not vanish when the cannabis does. More than half screen positive for anxiety and depression, and any plan that ignores that is a plan that fails. Cognitive behavioral therapy directed at cannabis use is the intervention with the most support. Cessation is simple to state and genuinely difficult to do, and pretending otherwise helps no one.

Why being believed is treatment

Which brings me back to bed nine. The single most therapeutic thing available to a patient with CHS is often the thing that costs nothing and gets withheld most: being believed. These are people who have usually been through the system many times, been labeled and discharged with a shrug, then sent back into a cycle no one bothered to name for them. Naming it accurately and telling them the truth about what will and will not help, without judgment, is not soft medicine. It is the treatment. A patient who understands what is happening to them and why walks out with something they did not have on the last four visits, which is a real reason to believe the next year can look different.

For a condition we still cannot fully explain, that turns out to be no small thing.

Being believed is where treatment begins.

Rick Pescatore, DO, is a board-certified emergency physician and the founder of BellyMD. This article is educational and is not medical advice. If you are vomiting uncontrollably or cannot keep fluids down, seek medical care.