Definition of carboxylation Cannabis, in its raw form, contains THCA, a compound that is distinctly different from TCA especially because it is not psychoactive. Upon smoking Cannabis, the THCA gives up its carboxylic group (-COOH) to form carbon dioxide gas and water vapor and THC. This is the process that is referred to as decarboxylation. THCA is one of the cannabinoid acids found in the plant, and which undergoes an alteration in its structure during drying or when heat is applied. This ...