THC (tetrahydrocannabinol) is the psychoactive compound in cannabis that produces a "high." It is created from THCA (tetrahydrocannabinol acid) through decarboxylation, which occurs when THCA is heated. This process transforms THCA into THC, resulting in the same effects associated with cannabis consumption. In summary, THCA is non-psychoactive in its raw form, but when heated, it becomes THC and produces psychoactive effects.