Abstract Objective: Two primary compounds of the cannabis plant (Cannabis sativa), delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD), differentially and dose-dependently affect mood and anxiety. In this systematic review, the authors summarize the design and results of controlled trials assessing the effects of THC and CBD on affective disorders, anxiety disorders, and posttraumatic stress disorder (PTSD). Methods: A keyword search of eight online literature databases identified eight randomized controlled trials of defined CBD or THC doses for the target populations. Results: A 1-month trial of daily THC (up to 3 mg per day) for DSM-II anxiety disorder reduced anxiety symptoms, but symptoms were very low throughout...