Cannabidiol (CBD) is a phytocannabinoid discovered in 1940. It is one of some 113 identified cannabinoids in cannabis plants and accounts for up to 40% of the plant's extract. In 2018, clinical research on cannabidiol included preliminary studies of anxiety, cognition, movement disorders, and pain. 
Cannabidiol can be taken into the body in multiple ways, including by inhalation of cannabis smoke or vapor, as an aerosol spray into the cheek, and by mouth. It may be supplied as CBD oil containing only CBD as the active ingredient (no included tetrahydrocannabinol [THC] or terpenes), a full-plant CBD-dominant hemp extract oil, capsules, dried cannabis, or as a prescription liquid solution. CBD does not have the same psychoactivity as THC, and may change the effects of THC on the body if both are present. As of 2018, the mechanism of action for its biological effects has not been determined. 
In the United States, the cannabidiol drug Epidiolex was approved by the Food and Drug Administration in 2018 for treatment of two epilepsy disorders. Since cannabis is a Schedule I controlled substance in the United States, other CBD formulations remain illegal to prescribe for medical use or to use as an ingredient in foods or dietary supplements.