Does medicinal cannabis affect depression, anxiety, and stress in people with cancer? A systematic review and meta-analysis of intervention studies.

Medicinal cannabis might have a role in supporting the mental health of people with cancer. This systematic review and meta-analysis examined the efficacy and safety of medicinal cannabis, compared with any control, as an intervention for depression, anxiety, and stress symptoms in people living with cancer. A secondary aim was to examine the effect of low versus high Δ-tetrahydrocannabinol (THC) dose on these outcomes. Five databases were systematically searched, and complemented with a snowball search from inception to May 2023, for any type of interventional study that included humans of any age with any cancer type. Primary outcomes were incidence and severity of depression, anxiety, and stress symptoms. Secondary outcomes were mood, cognition, quality of life, appetite, nutrition status, gastrointestinal symptoms, and adverse events. Data were pooled using Review Manager. Evidence was appraised using Cochrane risk of bias tools. Confidence in the estimated effect of pooled outcomes was assessed using GRADE. Fifteen studies (n=11 randomized trials, n=4 non-randomized trials) of 18 interventions (N=1898 total participants; 100% ≥18 years of age) were included. Ten studies examined THC (70% synthetic), two synthetic cannabidiol with or without THC, and six whole-plant extracts. No clinically significant effects of medicinal cannabis were found on primary outcomes. The likelihood of anxiety events increased with higher-dose synthetic THC compared with a lower dose (OR: 2.0; 95% CI: 1.4, 2.9; p<0.001; Confidence: very low). Medicinal cannabis increased the likelihood of improved appetite (OR: 12.3; 95% CI: 3.5, 45.5; p<0.001; n=3 interventions; Confidence: moderate) and reduced severity of appetite loss (SMD: -0.4; 95% CI: -0.8, -0.1; p=0.009; Confidence: very low). There was very low confidence that higher doses of synthetic THC increased the likelihood of any adverse event (OR: 0.5; 95% CI: 0.3, 0.7; p<0.001). Medicinal cannabis had no effect on emotional functioning, mood changes, confusion, disorientation, quality of life, and gastrointestinal symptoms. Confidence in findings was limited by some studies having high or unclear risk of bias and imprecise pooled estimates. There was insufficient evidence to determine the efficacy and safety of medicinal cannabis as a therapeutic intervention for depression, anxiety, or stress in people with active cancer.