Abstract Background: Medicinal cannabinoids, including medicinal cannabis, pharmaceutical cannabinoids and their synthetic derivatives, including tetrahydrocannabinol (THC) and or cannabidiol (CBD), have been suggested to have a therapeutic role for certain mental health conditions. The primary objective was to review the evidence for cannabinoids in treating symptoms of depression, anxiety, post-traumatic stress disorder, attention-deficit hyperactivity disorder, Tic/Tourette syndrome, and psychosis, either as the primary condition or secondary to other conditions. Secondary outcomes included quality of life and global functioning. Methods: We undertook a systematic review and meta-analysis of published and unpublished studies (1980-2018) using MEDLINE, Embase, PsycINFO, and Cochrane Central Register of Controlled Clinical Trials, clinicaltrials.gov,...