Does medicinal cannabis support the mental health of cancer survivors? A systematic review and meta-analysis of intervention studies

IntroductionMedicinal cannabis may have a role in supporting the mental health of cancer survivors. This study aimed to synthesize evidence on the safety and efficacy of medicinal cannabis, compared to any control, on depression, anxiety, and stress in cancer survivors.MethodsA systematic review with meta-analysis searched five databases to October 2022. Any type of intervention study, medicinal cannabis, comparator, cancer type/stage, and participant age were included. Depression, anxiety, and stress were primary outcomes. Secondary outcomes were mood, cognition, pain, sleep, fatigue, quality of life, appetite, nutrition status, and gastrointestinal symptoms. Data were pooled using RevMan. Evidence was appraised using the Cochrane RoB-2 or ROBINS-I tool and GRADE.ResultsSixteen studies (n=9 RCTs, n=5 controlled trials; n=2 uncontrolled trials) of 18 interventions and 1898 adults were included. Compared to control, medicinal cannabis (THC with or without CBD) had no overall effect on anxiety (n=9 studies reported no effect) nor depression (n=5 studies reported no effect). However, the likelihood of anxiety was increased by 100% with high dose THC compared to low dose (OR:2.0; 95%CI:1.42-2.90; n=2 interventions; GRADE: Low). One study found severity of anxiety, depression, and stress was reduced with THC/CBD (GRADE: Very low). Medicinal cannabis improved sleep and appetite but had no effect on pain, fatigue, confusion, appetite loss, constipation, dry mouth, and adverse events (asthenia, anaemia, hallucinations, feeling ‘high’, neoplasm progression). Medicinal cannabis increased likelihood of nausea, vomiting, drowsiness, headache, disorientation, and dizziness. Confidence in findings was limited by most studies having high or unclear risk of bias, small samples, heterogenous interventions, unvalidated primary outcome measures, and inadequate data reported for meta-analysis.ConclusionsThere was insufficient evidence to determine if medicinal cannabis has a role in supporting the mental health of cancer survivors. Future well-powered trials using validated outcome measures and full data reporting are warranted to confirm efficacy and safety