# THCA

> THCA (tetrahydrocannabinolic acid) is the acid cannabinoid that drug-type cannabis makes in its trichomes; heat or time decarboxylates it into THC, losing about 12% of its mass.

- Canonical: https://genetixbay.com/knowledge/glossary/thca.html
- Also written: THC-A, THCA-A, tetrahydrocannabinolic acid, Δ9-THCA, delta-9-THCA
- Glossary category: Cannabinoids and terpenes · Evidence: Established
- Status: Draft: awaiting expert review · Updated: 2026-10-31
- Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary"

THCA, Δ9-tetrahydrocannabinolic acid, is the main cannabinoid in drug-type cannabis. The enzyme [THCA synthase](https://genetixbay.com/knowledge/glossary/thca-synthase.md) builds it from [CBGA](https://genetixbay.com/knowledge/glossary/cbga.md) inside the [trichome head](https://genetixbay.com/knowledge/glossary/trichome-heads.md). THCA is not reported to be intoxicating in its own right; it becomes [THC](https://genetixbay.com/knowledge/glossary/thc.md) when its carboxyl group leaves as [CO2](https://genetixbay.com/knowledge/glossary/co2-enrichment.md), 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](https://genetixbay.com/knowledge/glossary/cbda.md) or both, through which synthase [alleles](https://genetixbay.com/knowledge/glossary/allele.md) it carries. Growers can't turn a CBDA plant into a THCA plant with feeding or light.

## Units and formula

Because the CO2 group weighs about 12.3% of the molecule, 1 g of THCA can yield at most [0.877](https://genetixbay.com/knowledge/glossary/total-thc.md) 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.

## Related terms

[THC](https://genetixbay.com/knowledge/glossary/thc.md), [Decarboxylation](https://genetixbay.com/knowledge/glossary/decarboxylation.md), [THCA synthase](https://genetixbay.com/knowledge/glossary/thca-synthase.md), [Total THC](https://genetixbay.com/knowledge/glossary/total-thc.md), [CBGA](https://genetixbay.com/knowledge/glossary/cbga.md), [Acid vs neutral cannabinoids](https://genetixbay.com/knowledge/glossary/acid-vs-neutral-cannabinoids.md)

## Read more

- [Buyer beware: potency labels, strain names and other claims that don't hold up](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md)
- [Chemotype inheritance: how THC and CBD synthase alleles pass on](https://genetixbay.com/knowledge/breeding/chemotype-inheritance.md)

## Sources

1. Sirikantaramas S, Morimoto S, Shoyama Y, et al. 2004. The gene controlling marijuana psychoactivity: molecular cloning and heterologous expression of Δ1-tetrahydrocannabinolic acid synthase from Cannabis sativa L. Journal of Biological Chemistry 279(38):39767-39774.
2. Wang M, Wang YH, Avula B, et al. 2016. Decarboxylation study of acidic cannabinoids: a novel approach using ultra-high-performance supercritical fluid chromatography/photodiode array-mass spectrometry. Cannabis and Cannabinoid Research 1(1):262-271.
3. Hanuš LO, Meyer SM, Muñoz E, Taglialatela-Scafati O, Appendino G. 2016. Phytocannabinoids: a unified critical inventory. Natural Product Reports 33(12):1357-1392.