Marijuana Extract THC Ineffective at Preventing Nausea Post-Surgery

The marijuana extract THC is ineffective at preventing postoperative nausea and vomiting.

The marijuana extract tetrahydrocannabinol (THC) is ineffective at preventing postoperative nausea and vomiting, according to research published in Anesthesia & Analgesia.

Postoperative nausea and vomiting (PONV) occurs at rates of 20% to 70% and can severely affect patients’ wellbeing. Recent trials have found that marijuana extracts are moderately successful in medical treatments; notably, dronabinol (synthetic d-9-THC), which was approved in the United States to prevent nausea and vomiting in patients undergoing chemotherapy.

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Maren Kleine-Brueggeney, MD, of the University of Bern in Switzerland, and colleagues evaluated the effectiveness of intravenous (IV) THC in preventing PONV, but found it ineffective. The relative risk reduction in patients who received THC was  12% (95% CI: -37% to 43%), less than the clinically significant 25% demonstrated by other drugs used to prevent PONV.

THC also caused widely-varying side effects such as increased sedation and confusion, as well as unacceptable extreme side effects in some patients. “Four patients in the THC group experienced pronounced side effects, such as extreme and sustained mood swings or anxiety, including one patient who was fighting and screaming when waking up. In the placebo group, only one patient experienced anxiety,” the researchers wrote.

For this study, Kleine-Brueggeney and colleagues identified 102 eligible patients out of 1885 patients undergoing elective surgical procedures, of whom 45 gave informed consent. Overall, 40 patients were randomly assigned to either receive 0.125 mg/kg IV THC or placebo after surgery before emergence from anesthesia. The researchers analyzed PONV for the first 24 hours after emergence, as well as early and late nausea and possible adverse effects.

The researchers stopped the trial after 40 patients because of THC’s relative ineffectiveness at preventing PONV, as well as its side effects. Results of logistic regression analysis adjusting for anesthesia time yielded an odd ratio of 0.95 (95% CI: 0.21 to 4.43, P = .97). Because previous research has found adverse effects associated with THC to be insignificant compared with commonly used drugs such as non-steroidal analgesics, the pronounced side effects in the current study were surprising.

“THC-treated patients showed longer times to emergence, higher sedation scores after emergence, and had almost statistically significant longer times until postanesthesia care unit (PACU) discharge criteria were met,” the researchers wrote.

Psychotropic adverse effects were also unpredictable, leading to patient satisfaction that varied as much as “best anesthesia ever” to “worst experience in my life.”

The researchers concluded that because they would have needed much larger sample sizes and because of the controversial findings of both the antiemetic and proemetic effects of THC, it would have been highly unlikely that they would have found a clinically relevant PONV-reducing effect of THC if they had continued the study.


  1. Kleine-Brueggeney M, Greif R, Brenneisen R, Urwyler N et al. Intravenous Delta-9-Tetrahydrocannabinol to Prevent Postoperative Nausea and Vomiting: A Randomized Controlled Trial. Anesthesia & Analgesia. 2015; doi:10.1213/ANE.0000000000000877.