The marijuana extract tetrahydrocannabinol (THC) isn’t effective at preventing nausea and vomiting after surgery in patients at high risk of this common complication, reports a study in Anesthesia & Analgesia.
What’s more, there were “unpredictable psychotropic and sedative side effects,” the study showed.
The study was halted after the first 40 patients because of “clinically unacceptable” side effects of THC, as well as questionable effects on PONV.
“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 postoperative nausea and vomiting (PONV) in high-risk patients,” conclude researchers who were led by Lorenz G. Theiler, MD, and colleagues of University of Bern, Switzerland.
The study included patients undergoing 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% relative reduction in PONV—the estimated effect of current medications to prevent nausea and vomiting (antiemetics).
The study 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% of patients experienced PONV during the first 24 hours after emerging from anesthesia.
The relative risk reduction with THC was just 12%—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.
The researchers note several limitations of their study, including questions about the best dose and timing of THC administration.