THCa stands for Tetrahydrocannabinolic acid, and is the precursor chemical to ordinary, everyday THC; THCa is the chemical compound found in all marijuana responsible for the creation of the psychoactive substance of THC during a process called decarboxylation. Decarboxylation, or the removal of a carbon and oxygen molecule, yields regular THC. This synthesized version is not considered a scheduled substance due to it’s chemical make-up functionally being the same as regular THCa, but with a couple molecules out of place to give it a unique identity from the scheduled substance, allowing for legal sale of THCa and its by-products.