THCa stands for tetrahydrocannabinolic acid. It’s a natural compound found in cannabis plants. THCa is actually the precursor to THC, which is the compound responsible for the psychoactive effects of marijuana.
In its raw form, cannabis doesn’t contain THC. Instead, it contains THCa. When you heat (decarboxylate) THCa by smoking, vaporizing, or cooking it, it loses a carboxyl group and releases carbon dioxide turning the THCa molecule into a THC molecule. This conversion is what makes cannabis psychoactive.
So, to put it simply, THCa is the non-psychoactive form of THC found in raw cannabis. It only becomes THC when it’s heated (decarboxylated).