THCa is the abbreviation of Tetrahydrocannabinolic acid which is found in undried cannabis but is gradually decarboxylated to THC with drying and particularly under intense heating.
THCa is the common ingredient of cannabis resin concentrates, such as hash oil or hashish when prepared from high THC products. It is innocuous but turns into intoxicating THC when exposed to heat through a process called decarboxylation. The acid has its medicinal potential in neuroprotective, antiemetic, and anti-inflammatory treatments.