During a shift in the emergency department at the Ramón y Cajal Hospital in Madrid, Beatriz Mexía treated a 19-year-old man with severe nausea, vomiting, and abdominal pain. “He could not tolerate even a sip of water and was dehydrated. We gave him intravenous fluids, but the usual anti-emetics could not stop the vomiting,” she recalls. This fourth-year family medicine resident, who works at the Los Alpes Health Center in Madrid, that night witnessed a chronic, common — but little-known in Spain, even among health staff — clinical scenario caused by daily cannabis or marijuana use: cannabinoid hyperemesis syndrome (CHS), characterized by severe, cyclical episodes of vomiting and nausea.

“It was the first time I had treated it and I was struck by how intense and long-lasting it was. A colleague showed me that heat relieves the symptoms. Those who know this take compulsive hot showers to ease them. An alternative is creams containing capsaicin” — a compound derived from hot chili peppers that produces a similar effect — Mexía explains. She presented the case at the Spanish Society of General and Family Physicians (SEMG) congress held last week in Oviedo. Heat eases the condition because receptors in the skin are connected to nerve circuits related to nausea.

According to a survey in the United States — the country where the syndrome has been most studied — “Among those who used cannabis daily, 17.8% reported CHS-like symptoms,” and of those “only 11.5% reported receiving a CHS diagnosis.” Those percentages imply that 7.3 million Americans suffer from this disorder to some degree (there are more than 40 million regular users in the country).

A small 2016 study by researchers at Hospital Clínic Barcelona of 22 patients who were stopping cannabis use — the only study of its kind in Spain and published in Emergencias, the journal of the Spanish Society of Emergency Medicine (SEMES) — found that 18.2% “reported having experienced symptoms” of the syndrome, a percentage very similar to that detected in the U.S. “CHS is a frequent entity, so we recommend asking about suggestive symptoms, as it causes a high degree of discomfort, diagnostic errors, and multiple specialist consultations,” the authors concluded.

The EDADES survey of the National Drug Plan for 2024 shows that 2.5% of people aged 15 to 64 in Spain use cannabis daily (about 825,000 people), so applying those percentages would indicate that around 150,000 may show CHS symptoms.

“It is a syndrome that was first described in 2004 and remains greatly under-diagnosed because it is little known among professionals and patients, despite these patients frequently requiring medical care,” explains Guillermo Burillo, head of the Toxicology working group at SEMES.

Specialists say several factors explain this. One is that “some people are reluctant to admit cannabis use” when attending a health center and being asked about it. Another is that episodes — if not properly treated — last 24 to 48 hours while the patient is under medical supervision. “Because there is no consumption during that time, the symptoms disappear without a proper diagnosis being made.” It also a factor that “cannabis is considered helpful in some cases to do the opposite: prevent nausea and vomiting in chemotherapy patients, which means doctors may not even consider it as a possible cause.”

The result is that many sufferers endure this syndrome for years without knowing the cause, without diagnosis, and without knowing how to act when symptoms appear. Burillo is the lead author of Spain’s largest case compilation, published in 2022 in the journal Medicina Clínica. The brief study — the most recent of its kind in Spain — included 59 attendances in the emergency department of the University Hospital of the Canary Islands corresponding to 29 patients between 2018 and 2019, representing 4.4 cases per 10,000 emergency visits. Half of those affected visited the hospital more than once, and three out of four were treated with topical capsaicin.

“The mean time to resolution of vomiting after its application was 17.87 minutes,” the study highlights. “This shows it is an effective treatment. Droperidol and haloperidol [two antipsychotics] or intravenous benzodiazepines are also useful. In Spain, more research is needed to gauge the real scale of the problem and to provide more training for health staff to identify the syndrome,” something Burillo is promoting through SEMES.

A large study that analyzed nearly 190 million U.S. hospital emergency visits between 2016 and 2022, published last November in the journal Emergency Medicine, detected a sudden rise in cases in recent years: “CHS increased from 4.4 per 100 000 visits, peaked at 33.1 in quarter 2 2020, and remained elevated at 22.3 in 2022,” the paper concluded. The highest-risk age group was 18 to 25, followed by 26 to 35.

Experts believe part of this increase may be due to better recognition of the condition by clinicians, allowing them to diagnose cases that previously went unnoticed. “But the rise is also surely influenced by increased consumption, something that has been extensively studied in the U.S. after recreational marijuana legalization in several states, where emergency visits have risen by 200%. Also relevant is the development of increasingly potent plant variants with higher concentrations of psychoactive substances. In Spain we do not have data confirming that CHS incidence is growing, but clinicians’ impression is that it is,” Burillo says.

A study by researchers at George Washington University last year found that 85% of CHS sufferers had visited an emergency department at least once and that “44% had to be hospitalized because of the severity of the crises.” Among the patients analyzed, 40% said they used cannabis more than five times a day before the syndrome began and 44% reported using the substance for more than five years.

On why some users develop CHS and others do not, Burillo admits the mechanisms are not fully understood: “The most plausible hypothesis is genetic factors that make some people more prone. Another is that certain pesticides used in plant cultivation may play a role.”

The author of the clinical case presented at the SEMG congress warns of the considerable impact CHS has on patients’ lives, even though complications are uncommon (scientific literature does record cases of esophageal perforation and tears due to the intensity of vomiting). “The most important thing is to manage hydration well. But the syndrome is highly disabling because of the intensity of the symptoms. This can significantly interfere with daily life for those with more cyclical crises,” Mexía explains.

The specialist stresses that “the only way to definitively prevent CHS is to stop using cannabis, which also prevents the development of psychiatric disorders whose links to the substance are established, especially among younger users.”

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