Cannabidiol (CBD) is a phytocannabinoid discovered in 1940. It is one of some 113 identified cannabinoids in Cannabis plants, accounting for up to 40% of the plant's extract. As of 2018, preliminary clinical research on cannabidiol included studies of anxiety, cognition, movement disorders, and pain.Cannabidiol can be taken into the body in multiple different 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 added 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 affect the actions of THC. Although in vitro studies indicate CBD may interact with different biological targets, including cannabinoid receptors and other neurotransmitter receptors, the mechanism of action for its possible biological effects has not been determined, as of 2018.In the United States, the cannabidiol drug Epidiolex has been approved by the Food and Drug Administration for treatment of two epilepsy disorders. Side effects of long-term use listed on the Epidiolex label include somnolence, decreased appetite, diarrhea, fatigue, malaise, weakness, sleeping problems, and others.The U.S. Drug Enforcement Administration has assigned Epidiolex a Schedule V classification while non-Epidiolex CBD remains a Schedule I drug prohibited for any use. CBD is not scheduled under any United Nations drug control treaties, and in 2018 the World Health Organization recommended that it remain unscheduled.