THCA (short for tetrahydrocannabinolic acid) is the precursor molecule to THC. It occurs naturally in raw cannabis (whereas THC doesn’t) and converts to THC when the flower is exposed to heat and light.When cannabis is dried and cured, THCA slowly becomes THC. This is why inhaling marijuana has such a strong effect; it’s full of potent THC molecules that were created from THCA. THCA isn’t the only cannabinoid acid you’ll find in cannabis.