Marijuana extract doesn't reduce postoperative nausea, vomiting

Intravenous THC had a "negligible" effect on postoperative nausea and vomiting (PONV), as well as "unpredictable psychotropic and sedative side effects," according to the clinical trial by Dr. Lorenz G. Theiler and colleagues of University of Bern, Switzerland. At a time of growing interest in the uses of medical marijuana, the results suggest that marijuana compounds (cannabinoids) aren't a good option to prevent PONV.

No Benefit of Medical Marijuana for PONV

The study included patients undergoing surgical procedures (gynecological or breast surgery) associated with a high risk of PONV. Patients were randomly assigned to receive a "relatively high" dose of intravenous THC or an inactive placebo. Both treatments were given toward the end of surgery, before emergence from general anesthesia.

Rates of PONV were compared between groups. The original study design called for enrollment of about 300 patients, to detect a "clinically significant" 25 percent relative reduction in PONV -- the estimated effect of current medications to prevent nausea and vomiting (antiemetics).

However, the trial was halted after the first 40 patients because of "clinically unacceptable" side effects of THC, as well as questionable effects on PONV. In both the THC and placebo groups, about 60 to 70 percent of patients experienced PONV during the first 24 hours after emerging from anesthesia.

The relative risk reduction with THC was just 12 percent -- well under the clinically significant cutoff point. The effect was even weaker after adjustment for differences in anesthesia time.

Meanwhile, there were major problems with side effects. Patients receiving THC took longer to emerge from anesthesia, were more sedated after emergence, and tended to remain in the recovery room longer. The THC group needed less pain medication for the first few hours, possibly because of their increased sedation.

Mental or mood (psychotropic) side effects were "unpredictable in both quantity and quality" in the THC group. "Patients' satisfaction varied enormously from 'best anesthesia ever' to 'worst experience of my life,'" the researchers add.

Nausea and vomiting after surgery is a common problem that can lead to serious complications. Current antiemetic drugs can reduce but not eliminate PONV. Past reports have suggested that marijuana compounds (cannabinoids) may prevent nausea and vomiting during cancer chemotherapy.

Marijuana extracts have also been suggested for prevention of PONV, but the evidence is "very limited and inconclusive." Most previous studies have used synthetic oral cannabinoids, with conflicting results.

Dr. Theiler and colleagues conclude, "Due to an unacceptable side effect profile and uncertain antiemetic effects, intravenous THC administered at the end of surgery prior to emergence from anesthesia cannot be recommended for the prevention of PONV in high-risk patients." The researchers note several limitations of their study, including questions about the best dose and timing of THC administration.