THCA, Δ9-tetrahydrocannabinolic acid, is the main cannabinoid in drug-type cannabis. The enzyme THCA synthase builds it from CBGA inside the trichome head. THCA is not reported to be intoxicating in its own right; it becomes THC when its carboxyl group leaves as CO2, a reaction driven by heat (smoking, vaping, baking) and, slowly, by storage.
In practice
A good drug-type flower COA might show THCA at 20% w/w and Δ9-THC at 0.6% w/w. The plant's genetics set whether it makes mostly THCA, mostly CBDA or both, through which synthase alleles it carries. Growers can't turn a CBDA plant into a THCA plant with feeding or light.
Because the CO2 group weighs about 12.3% of the molecule, 1 g of THCA can yield at most 0.877 g of THC. Total THC = Δ9-THC + 0.877 × THCA.
Don't confuse with
- THC: the neutral, decarboxylated product.
- THCA diamonds: a concentrate made of crystallised THCA, not a different compound.
- Total THC: a calculated label figure combining THCA and THC.
THCA synthase is the trichome enzyme that converts CBGA into THCA; which alleles of its gene a plant carries largely decides whether it is THC-dominant.CBGA (cannabigerolic acid) is the precursor cannabinoid that the plant converts into THCA, CBDA or CBCA, formed by joining olivetolic acid to geranyl pyrophosphate.Trichome heads are the bulbous resin-filled tops of capitate glandular trichomes, where cannabis makes and stores nearly all its cannabinoids and terpenes; they are the raw material of hash.THC (Δ9-tetrahydrocannabinol) is the neutral, decarboxylated cannabinoid mainly responsible for cannabis's reported intoxicating effects; the living plant makes it almost entirely as THCA.CO2 enrichment raises carbon dioxide in a sealed grow space from about 420 ppm to roughly 800–1,500 ppm, letting plants use higher light intensities productively.CBDA (cannabidiolic acid) is the acid cannabinoid made by CBDA synthase from CBGA; it dominates hemp-type and CBD-type cannabis and decarboxylates to CBD.An allele is one version of a gene; a diploid cannabis plant carries two alleles at each locus, one from each parent, which may be the same or different.Total THC is a calculated figure, Δ9-THC plus 0.877 × THCA, estimating the maximum THC a sample could yield after full decarboxylation.Decarboxylation is the loss of a carboxyl group as CO2 that turns acid cannabinoids such as THCA and CBDA into neutral THC and CBD, quickly with heat, slowly with time.Acid cannabinoids (THCA, CBDA, CBGA) are the carboxylated forms the plant makes; neutral cannabinoids (THC, CBD, CBG) form when heat or time removes the carboxyl group.
