A large systematic review and meta-analysis published in the Lancet Psychiatry found little evidence for the efficacy and safety of medicinal cannabinoids, including cannabidiol (CBD) and tetrahydrocannabinol (THC), as treatment for mental disorders. The study emphasizes the need for further research concerning a treatment that is increasingly being legalized and applied to a wide range of medical conditions.
Researchers searched major databases for studies published between January 1980 and April 2018 that included adults who received any form of medicinal cannabinoid for the treatment of various mental disorders, including attention-deficit hyperactivity disorder (ADHD), anxiety, depression, post-traumatic stress disorder (PTSD), Tourette syndrome, and psychosis. Primary outcomes included remission or symptom alterations. Safety, risk of bias, and quality of evidence were also assessed.
Of 83 total eligible studies, 40 were randomized controlled trials. Depression was the focus of 42 studies, anxiety of 31, Tourette syndrome of 8, ADHD of 3, PTSD of 12, and psychosis of 11.
In terms of efficacy, pharmaceutical THC (plus or minus CBD) reduced anxiety symptoms in patients with co-morbid medical conditions, such as multiple sclerosis and chronic non-cancer pain (standardized mean difference [SMD], -0.25; 95% CI, -0.49 to -0.01), but the quality of evidence was considered low as none of the 7 studies included patients with a primary anxiety diagnosis. Of note, primary outcomes for other disorders were not significantly affected.
For safety, 1 study demonstrated that pharmaceutical THC (plus or minus CBD) aggravated negative symptoms of psychosis (SMD, 0.36; 95% CI, 0.10-0.62). In addition, across studies, the number of people experiencing adverse events increased as a result of pharmaceutical THC (odds ratio (OR), 1.99; 95% CI, 1.20-1.39), as did withdrawals due to adverse events (OR, 2.78; 95% CI, 1.59-4.86), when compared with placebo.
The researchers wrote, “There remains insufficient evidence to provide guidance on the use of cannabinoids for treating mental disorders within a regulatory framework.”
The study was limited by a lack of available research on cannabinoid treatments with mental disorders as the primary target. “Further high-quality studies directly examining the effect of cannabinoids on treating mental disorders are needed,” they concluded.
Black N, Stockings E, Campbell G, et al. Cannabinoids for the treatment of mental disorders and symptoms of mental disorders: a systematic review and meta-analysis [published online October 28, 2019]. Lancet Psychiatry. doi:10.1016/S2215-0366(19)30401-8