THCa flower is a type of cannabis flower that has high levels of THCa (tetrahydrocannabinolic acid). THCa itself, is the precursor to THC. THCa flower is cannabis flower that’s been harvested before the THCa has been converted into THC during its maturation. While raw THCa isn’t psychoactive, when it’s exposed to heat (like vaping or smoking), it turns into THC and becomes psychoactive.