What is the evidence supporting the use of medical cannabis?

Cannabis-related products are not well studied and when they have been they have come up short in the treatment of most mental disorders, including Tourette's, depression, attention deficit hyperactivity disorder, post-traumatic stress disorder, psychosis, and anxiety. Pharmaceutical grade tetrahydrocannabinol (THC) provides a small benefit in anxiety symptoms in patients with chronic noncancer pain and multiple sclerosis. Though not included in this review, the <a href="https://www.bmj.com/content/367/bmj.l6453">UK National Institute for Health and Care Excellence recommends cannabidiol</a> for seizures associated with Lennox-Gastaut syndrome and Dravet syndrome, as well as to controls spasms and spasticity associated with multiple sclerosis (LOE = 2a-)

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. Lancet Psychiatry 2019 https://doi.org/10.1016/S2215-0366(19)30401-8.  [PMID:31672337]

Meta-analysis (other)

Government

Various (meta-analysis)

This meta-analysis identified 83 randomized and nonrandomized studies that investigated the effectiveness of cannabis or cannabinoids (the active ingredients in cannabis) in the treatment of various mental problems by searching 4 databases as well as unpublished and ongoing studies. Two authors independently selected articles for inclusion, abstracted the data, and graded study quality; they also evaluated relevance and directness of results along with risk of bias. Overall, the quality of evidence is low, which is no surprise since there is no mega-pharma company with patent exclusivity requiring governments and other groups to develop the database. Despite many studies, cannabinoid (THC or cannabidiol) treatment has not been shown to be effective for depression, psychosis, or anxiety. Cannabinoids have been studied, without evidence of benefit, in patients with Tourette syndrome, adult attention-deficit/hyperactivity disorder, and posttraumatic stress disorder. Pharmaceutical-grade THC (7 studies, 252 patients) improves anxiety symptoms in patients with chronic noncancer pain and multiple sclerosis, though the effect size is small (standardized mean difference = .25).