Short answer
THCA (tetrahydrocannabinolic acid) is the form of THC the cannabis plant actually makes. Fresh and dried buds are mostly THCA; heat turns it into THC. Labels give total THC = THC + 0.877 × THCA, so 30% THCA is about 26% total THC. Established chemistry.
Why
The plant makes acids. Secretory cells in the glandular trichomes make cannabinoid acids, THCA among them, and store them in the gland head [2]. They become neutral THC mainly by heat, not on the living plant [3].
Heat knocks off a carbon dioxide. That reaction, decarboxylation, was measured at 80–145 °C: THCA converted to THC following first-order kinetics, faster at higher temperatures, and faster than CBDA or CBGA [1]. Smoking, vaping and baking all do it.
The 0.877 factor is just molecular weight. THC weighs about 314.5 g/mol and THCA about 358.5 g/mol, so 1 g of THCA can become at most 0.877 g of THC. Real conversion is usually less than complete.
Labels can run high. A retest of retail flower found many products below their labelled THC [4]. GenetixBay's position: flower labelled above about 35% total cannabinoids isn't credible.
The numbers
| Measure | Meaning | Example |
|---|---|---|
| THCA % | Acid form in the bud | 25% |
| THC % (delta-9) | Already neutral; usually small in fresh flower | 1% |
| Total THC | THC + 0.877 × THCA | 1 + 21.9 ≈ 22.9% |
| 0.877 | 314.5 ÷ 358.5 g/mol | — |
| Ceiling for flower | Total cannabinoids above ~35% not credible | — |
What to do
- Read a certificate of analysis for both THCA and THC, and the total.
- Treat "THCA flower" as ordinary cannabis: heat converts it.
- Store buds cool, dark and airtight to slow conversion and oxidation.
- Check local rules: some places regulate by total THC, others by delta-9 only.
Common mistakes
- Thinking high-THCA flower is "not THC".
- Adding THCA and THC without the 0.877 factor.
- Trusting a 40%+ flower label.
Related
- Full article: Buyer beware: label claims
- Answers: THC vs CBD plants · checking trichomes
- Article: Cannabis plant biology
- Terms: THCA · decarboxylation · total THC
