Glossary
THCa (tetrahydrocannabinolic acid)
Updated:
Tetrahydrocannabinolic acid, or THCa, is the non-intoxicating acid form of THC that the plant makes. Heat converts it to delta-9 THC. USDA counts it in total THC using the factor 0.877, and the federal hemp definition will include it from December 11, 2026.
The cannabis plant does not make delta-9 THC directly. It makes tetrahydrocannabinolic acid, which is not intoxicating on its own. Applying heat removes a carboxyl group and converts THCa into delta-9 THC (7 CFR 990.1). Smoking, vaping and baking all do this within seconds to minutes.
USDA's hemp testing rules define total THC as delta-9 THC plus 0.877 times THCa. The factor reflects the loss of mass when the carboxyl group leaves (7 CFR 990.1). So flower showing 20 percent THCa holds about 17.5 percent potential delta-9 THC after heating.
The 2018 Farm Bill definition measured only delta-9 THC, which allowed THCa-rich flower to be sold as hemp. Section 781 of Public Law 119-37 rewrote the definition to use total tetrahydrocannabinols, including tetrahydrocannabinolic acid (7 U.S.C. 1639o). Public Law 119-103 delayed that part of the change until December 11, 2026 (P.L. 119-103). After that date, flower that passes only on delta-9 THC no longer qualifies as hemp.
On a certificate of analysis, THCa and delta-9 THC appear as separate lines, and a total THC line combines them.
Sources
- 7 CFR 990.1, Meaning of terms (Domestic Hemp Production Program) Cornell Legal Information Institute (accessed 2026-10-13)
- 7 U.S.C. 1639o, Definitions (hemp) Cornell Legal Information Institute (accessed 2026-10-13)
- Public Law 119-103, Continuing Appropriations and Extensions Act, 2027, section 2019 GovInfo (accessed 2026-10-13)