While there are many studies on cannabinoids for the treatment of mental disorders and symptoms of mental disorders – to date there are very few high quality studies. A meta-analysis published in Lancet Psychiatry in October 2018 reviewed research where a mental health target was the primary outcome of the study. The paper reports on 42 studies for depression and 11 for psychosis where mainly CBD or THC was used. The authors report no benefit for depression and none for psychosis. But they do report harm in one of the 11 studies in psychosis noting that cannabinoids made negative symptoms worse. To date, there appears to be little high quality evidence supporting the use of cannabinoids in depression or schizophrenia. There are also single studies showing potential uses in schizophrenia and more research in ongoing.
Black N, Stockings E, Campbell G, Tran LT, Zagic D, Hall WD, Farrell M, Degenhardt L. Cannabinoids for the treatment of mental disorders and symptoms of mental disorders: a systematic review and meta-analysis. The Lancet Psychiatry. 2019 Oct 28.
McGuire P, Robson P, Cubala WJ, Vasile D, Morrison PD, Barron R, Taylor A, Wright S. Cannabidiol (CBD) as an adjunctive therapy in schizophrenia: a multicenter randomized controlled trial. American Journal of Psychiatry. 2017 Dec 15;175(3):225-31.