The Most Comprehensive Systematic Review of CHS: 183 Studies, 14 Diagnostic Features, and Treatment Options

The Systematic Review

Cecilia Sorensen and colleagues — an interdisciplinary team spanning emergency medicine, pharmacy, psychology, and toxicology at the University of Colorado and Denver Health — conducted the most comprehensive systematic review of cannabinoid hyperemesis syndrome (CHS) to date.

The review searched five major databases from January 2000 through September 2015, screened 2,178 articles, removed duplicates to review 1,253 abstracts, and ultimately included 183 studies. The majority were case reports and case series — the nature of a syndrome that had only been formally named thirteen years earlier.

The Diagnostic Profile

The cumulative synthesis produced the clearest clinical picture of CHS available anywhere in the medical literature.

The diagnostic pattern is striking in its consistency. CHS is not a vague, subjective diagnosis. It is a syndrome with a nearly pathognomonic feature — compulsive hot bathing — that no other common cause of cyclic vomiting produces. Emergency physicians who know to ask about cannabis use and hot shower behavior can make the diagnosis at the bedside in minutes, potentially saving thousands of dollars in unnecessary testing.

The Three Phases

The review confirmed that CHS follows a characteristic three-phase pattern first described in the early case literature:

The Paradox: Why Does Cannabis Cause Vomiting?

This is the question that makes CHS so scientifically fascinating. Cannabis is among the most effective anti-emetics known — it has been used for chemotherapy-induced nausea since the 1970s and is FDA-approved for this purpose (as dronabinol and nabilone). How can the same substance that prevents vomiting also cause uncontrollable vomiting?

The Sorensen review was candid about the limits of understanding: the pathophysiology section concluded that the mechanisms remain "unclear" with a "dearth of research dedicated to investigating its underlying mechanism." This honesty is important — CHS is a clinical reality whose biological explanation is still being worked out.

The Treatment Landscape

The failure of standard anti-emetics is itself a diagnostic feature. When a chronic cannabis user presents with cyclic vomiting that does not respond to ondansetron but improves dramatically with hot water, the diagnosis is almost certainly CHS. This pattern distinguishes it from cyclic vomiting syndrome and virtually all other causes of recurrent vomiting.

From Obscure Case Report to Emergency Department Epidemic

When J.H. Allen first described the syndrome in 2004 — a case series of 19 patients in South Australia, 9 of whom met criteria for the full syndrome — it was a medical curiosity. Most physicians had never heard of it. Many did not believe it was real.

The numbers are stark. CHS-related emergency department visits in the United States increased roughly seven-fold between 2016 and 2020. In states with legalized recreational cannabis, rates were more than double those in non-legalized states. The increasing potency of modern cannabis products — concentrates, vapes, edibles with precise high doses — appears to be a key driver. CHS is no longer rare. It is a routine part of emergency medicine practice in any state with legal cannabis.

What People Get Wrong

Myth vs. Reality

✕Myth

CHS only affects people who smoke enormous amounts of cannabis

✓Reality

While heavy daily use is the typical pattern, the Sorensen review found that 'regular cannabis for any duration of time' was present in 100% of cases, and the specific threshold for developing CHS is unknown. Some patients develop CHS after relatively modest use — the susceptibility appears to involve individual genetic and metabolic factors, not just quantity consumed.

The Evidence

Sorensen et al. (2017); Russo (2022) genomic investigation

The most dangerous misconception about CHS is the belief that it cannot happen to you. Many patients with CHS initially refuse to accept the diagnosis because they have used cannabis for years without problems. The prodromal phase — increased nausea treated with more cannabis — can last months or years before the full hyperemetic crisis hits. During this phase, patients are often told by fellow cannabis users (and sometimes by uninformed healthcare providers) that cannabis should help their nausea, creating a vicious cycle of increasing use and worsening symptoms.

The Bigger Picture

CHS matters far beyond the emergency department. It is a natural experiment in what happens when the endocannabinoid system is chronically overstimulated — a living demonstration of receptor desensitization, dose-response reversal, and the difference between acute pharmacology and chronic adaptation.

For the broader cannabis conversation, CHS serves as a corrective to the notion that cannabis is entirely benign. It is not. At high doses over extended periods, it can produce a syndrome so severe that patients end up in the emergency department repeatedly, undergo unnecessary surgeries, lose weight dangerously, and in rare documented cases, die from complications including dehydration-related kidney failure and cardiac events.

But CHS is also treatable — with the simplest intervention imaginable: stop using cannabis. The recovery rate approaches 97%. For a syndrome that can be utterly debilitating, the cure is complete and available to everyone.

Frequently Asked Questions

How do I know if I have CHS versus regular food poisoning or a stomach bug?

The key distinguishing features: CHS is cyclical (it comes back), it occurs exclusively in regular cannabis users, standard anti-nausea medications do not work, and hot showers or baths provide dramatic temporary relief. If you use cannabis regularly and have had multiple episodes of severe vomiting that seem to defy diagnosis, CHS should be strongly considered. Our full CHS guide walks through the diagnosis step by step.

Can I keep using cannabis if I reduce my intake?

The evidence from this systematic review is clear: reducing cannabis use does not resolve CHS. Complete cessation was required in essentially all successfully treated cases. Even patients who reduced to occasional use frequently relapsed into the hyperemetic cycle. The syndrome resolves only with full abstinence.

Why do hot showers help?

The leading theory involves the TRPV1 receptor — the same receptor activated by capsaicin (chili pepper heat). TRPV1 is coexpressed with CB1 cannabinoid receptors in the gut. Hot water activates TRPV1 in a way that may temporarily restore the balance disrupted by chronic CB1 desensitization. This is also why topical capsaicin cream applied to the abdomen can provide similar relief.

How common is CHS?

More common than previously thought and increasing. One study found that approximately 32.9% of daily or near-daily cannabis smokers in an urban ED met criteria for CHS. Emergency department visits for CHS increased roughly seven-fold in the US between 2016 and 2020. As cannabis potency and availability increase, CHS rates are expected to continue rising.