THC is an abbreviation for tetrahydrocannabinol. It is the most well-known and most abundantly available cannabinoid in marijuana plants. THC is also the component in marijuana that is responsible for the psychoactive effects, or the “high.” Also known as delta-9-tetracannabinol, it was first isolated in 1964 and is thought to serve as a natural defense for the plant against pests. Research has shown THC to be an effective medical treatment for a range of conditions. There is no lethal dose of the compound in its natural form.