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Cannabis has been used for millennia to treat nausea and vomiting, among many other ailments. In 2017, the National Academy of Medicine confirmed that many scientific studies have proven the effectiveness of cannabis as a treatment for chemotherapy-induced nausea and vomiting (N/V). But this is only half the story of cannabis’s impact on nausea and vomiting.

Many drugs have biphasic effects. This means that a low dose of the drug has one effect, while higher doses have the opposite effect. Cannabis has biphasic effects in a variety of ways. For example, most people find lower doses of cannabis have a calming effect, lowering anxiety.

However, it is well documented that an increasing number of people become anxious and even panicky as higher doses of cannabis are ingested. This biphasic, dose-dependent paradoxical effect is also sometimes present regarding cannabis and N/V.

CHS History

Episodic bouts of recalcitrant vomiting induced by cannabis were first described in 2004. This functional gut-brain axis disorder is called Cannabis Hyperemesis Syndrome (CHS), derived from the Greek word “emein”, meaning “to vomit”. As high-concentration cannabis products became more available to increasing numbers of people due to spreading legalization, the frequency of CHS reports has also increased.

Often seen in emergency departments, CHS occurs because of long-term, heavy use of cannabis, although it has proven difficult to determine how long-term and how heavy cannabis use needs to be to cause CHS. Two recent articles provide most of the information contained in the following post: A Perisetti, et al (2020) and H. Senderocich, et al (2022).

The prodromal phase of CHS is characterized by nausea, abdominal discomfort, and fear of vomiting. The active phase of vomiting comes in episodes, often induced by ingesting cannabis. The vomiting phase often drives people to seek help in hospital emergency departments. where severe dehydration and electrolyte imbalance sometimes lead to costly hospitalization. When not recognized as cannabis-related, persistent vomiting can lead to unnecessary invasive medical tests and procedures. When not treated, people have occasionally experienced serious tears in their esophagus, and even a rare death.

CHS Causes

The cause of CHS is not known in detail. The endocannabinoid system is active in the intestine, and cannabis has multiple effects on the gastrointestinal system, including secretions, appetite stimulation, modulation of inflammation, and motility. The natural cannabinoids anandamide and 2-AG both activate cannabinoid receptors in the gut to produce anti-emetic properties.

Current theories suggest one or all the following mechanisms for CHS: THC overrides CB1 receptors that have been reduced in number by long-term heavy use, stress releases excess THC stored in fat cells, and/or genetic differences in the liver’s P450 enzyme system’s metabolism of THC. More needs to be revealed by ongoing research.

How long is long-term? One study says the average duration before the onset of CHS is 16 years, while another reports the case of an adolescent after six months, as well as cancer patients. Once an episode of CHS begins, refractory vomiting can last hours, to weeks.

Hot Showers and Baths

Currently, there is no reliable management regime except total abstinence from cannabis, and it can take up to 3-6 months to heal CHS. Many suffering from CHS have discovered hot showers and hot baths temporarily relieve symptoms. This discovery is so common that some researchers suggest compulsive hot water therapy is a valuable diagnostic clue.

The only other proven treatments are topical capsaicin crème and intravenous haloperidol. Both hot water and capsaicin divert blood from the intestines to the skin (activating TRPV1 and reducing Substance P). Standard antinausea medications, such as ondansetron, prochlorperazine, and promethazine, are not as effective. Since no treatment is reliable, benzodiazepines, propranolol, droperidol (a dopamine antagonist), and aprepitant (a neurokinin 1 receptor antagonist) have all been tried and reported to have potential benefits.

I included the above list of medications for the treatment of CHS in case any physician or emergency department professional reads this post. Awareness is the key to helping anyone unfortunate enough to be struck by CHS. Unless medical professionals are aware of CHS and ask about cannabis use, their patients will not get the care they need.

I have not found any reliable estimate of CHS prevalence, although articles by emergency room physicians use words like “common” and “very frequent."

Conclusion

The bottom line for therapists and the general public is twofold.

First, be aware: Nausea, abdominal discomfort, and vomiting in any cannabis user may be signs of CHS, as well as signs that the frequency and duration of cannabis use are likely more than initially acknowledged.

And second, abstinence is the commonsense response to CHS, although abstinence is likely far easier to advise than to accomplish. Considerable support may be necessary to achieve abstinence after a long history of very frequent cannabis use. Medication may be necessary to avoid the worse consequences of CHS, but it is hardly the best idea to use in order to continue using cannabis.