The effectiveness of smoked cannabis and prescription cannabinoids like nabilone (Cesamet®), dronabinol (Marinol®), and levonantradol in the treatment of chemotherapy-induced nausea and vomiting (CINV) has been studied through systematic reviews, meta-analyses, and clinical trials. One meta-analysis of 28 randomized controlled trials involving 2,454 participants reported that prescription cannabinoids were more effective than both active comparators and placebo in reducing CINV, but statistical significance was not reached in all of the studies. Patients who received prescription cannabinoids experienced a greater anti-nausea and vomiting response than those who received a placebo.

While prescription cannabinoids have advantages over a placebo, randomized clinical trials indicate that cannabinoids are only slightly better than conventional anti-emetics that target dopamine D2 receptors. Patients have reported preferring cannabinoids to conventional therapies, despite experiencing adverse effects such as drowsiness, dizziness, dysphoria, depression, hallucinations, paranoia, and arterial hypotension. This preference may be due, in part, to the sedative and euphoric effects of cannabinoids, which some patients perceive as beneficial during chemotherapy.

Clinical trials of smoked cannabis for the treatment of CINV are lacking, but one review of US state clinical trials found that patients who smoked cannabis or took a Δ9-THC capsule reported significant relief from nausea and vomiting. Plasma levels of > 10 ng/mL Δ9-THC were associated with the greatest suppression of nausea and vomiting.

In one small open label trial, children with various blood cancers were administered Δ8-THC (18 mg/m2) two hours before chemotherapy and every six hours for the next 24 hours. The trial found that Δ8-THC prevented vomiting and did not cause delayed nausea or vomiting episodes. Δ8-THC was administered at doses higher than those typically given to adult patients with no significant side effects.

Few direct clinical trials have compared cannabinoids to newer anti-emetics such as 5-HT3 (Ondansetron, Granisetron) or NK-1 receptor antagonists, although animal studies show that the combination of low doses of Δ9-THC and low doses of the 5-HT3 receptor antagonists ondansetron or tropisetron may be more effective in reducing nausea and emesis frequency than when administered individually.

A retrospective chart review of dronabinol use for CINV in an adolescent oncology population found that the majority of patients who received moderate or highly emetogenic chemotherapy and standard anti-emetic therapy also received dronabinol. Sixty percent of the pediatric patients in this study reported a “good” response to dronabinol.

Reference info: https://www.canada.ca/en/health-canada/services/drugs-medication/cannabis/information-medical-practitioners/information-health-care-professionals-cannabis-cannabinoids.html#a4.1