Legalization of cannabis for medical or recreational purposes is catching on in the United States and Canada. Although useful as an antiemetic for patients with various conditions, the drug can also lead to cannabinoid hyperemesis syndrome (CHS) in longtime users, which causes nausea and vomiting. An article in the September issue of Clinical & Forensic Toxicology News (CFTN) discusses this paradox, and how to recognize and treat CHS.

Patients with this condition can suffer for years before being diagnosed properly, which results in repeat emergency room visits and skyrocketing medical costs. “Prompt recognition and diagnosis can avoid unnecessary and expensive medical investigations and provide relief to the patient,” according to the article’s author Grace Mahony Kroner, PhD, a clinical chemistry fellow at the University of Utah/ARUP Laboratories in Salt Lake City.

CFTN is a quarterly AACC/College of American Pathologists (CAP) educational newsletter for toxicology laboratories and individuals with an interest in toxicology. Each issue highlights topics of interest to the clinical and forensic toxicology fields.

In her article, Kroner explains why a drug intended to relieve gastrointestinal symptoms might exacerbate such symptoms after long-term use. Activation of the CB1 cannabinoid receptor in the central nervous system and enteric nerves “is thought to be the main mechanism by which cannabinoids exert their antiemetic effect because activation of these receptors inhibits emetic neurotransmitter signaling … Researchers have proposed that downregulation or desensitization of the CB1 receptors due to excessive exposure to their cannabinoid ligands may produce an emetic effect by disrupting the endogenous cannabinoid system,” according to Kroner.

However, “the physiological control of nausea and vomiting is complex, so there are likely other influences on cannabis’ antiemetic effect,” she added. The buildup of cannabinoids in fat or variant metabolism may lead to nausea and vomiting. Animal models have revealed that delta-9-tetrahydrocannabinol, a critical mediator of hundreds of compounds in cannabis, suppressed vomiting, but another type of cannabinoid, cannabidiol, actually increased it.

Kroner also describes how patients with CHS present, and why baths and showers appear to relieve symptoms. “First, the hot water may correct cannabinoid-mediated disruption of the hypothalamic thermoregulatory system, thus decreasing symptoms. Second, the diversion of blood from the abdominal circulation to the skin due to the temperature increase may relieve symptoms,” she explains.

Common treatments for CHS include intravenous hydration and supportive therapy. Antipsychotic drugs such as haloperidol or olanzapine, or topical capsaicin are prescribed when appropriate to relieve symptoms. Mahony specifically addresses the dangers of using opiates as a therapy for CHS due to their addictive properties and tendency to cause nausea.

Abstaining from cannabis is the only true cure for CHS, Kroner emphasizes. “Patient education is therefore critical, and patients should be informed that it may take up to 10 days for symptoms to disappear after stopping use of cannabis,” she indicated.

CFTN is an educational service of the Forensic Urine Drug Testing (FUDT) Accreditation Program co-sponsored by AACC and CAP. Individual subscriptions are also available; the regular price is $65, and AACC members pay $45. Subscribers are eligible to receive four ACCENT continuing education credits per year, one credit per quarterly issue.