What is THCa? THCa, or tetrahydrocannabinolic acid, is a cannabinoid found in the cannabis plant. It is the precursor to THC (tetrahydrocannabinol), the well-known psychoactive compound in cannabis. THCa itself does not produce the psychoactive effects commonly associated with THC because it needs to be decarboxylated, a process that involves heating the compound.When cannabis is heated, either through smoking, vaporization, or cooking, THCa undergoes decarboxylation and transforms into THC. This process releases carbon dioxide (CO2) and activates the psychoactive properties of THC. The decarboxylation process occurs naturally over time as cannabis plants dry and age.