THCA (tetrahydrocannabinolic acid) is the form THC takes inside the growing cannabis plant. Fresh and dried flower contains mostly THCA, not THC. When cannabis is heated, by lighting a joint, vaping or baking, THCA loses part of its molecule and becomes THC. That is why a flower label lists a lot of THCA and very little THC, and why New York labels report total THC. Here is how it works.
Quick Facts
- THCA Tetrahydrocannabinolic acid, the acidic form of THC made by the plant
- Turns into THC When heated, in a process called decarboxylation
- On New York labels Total THC = THC + (THCA × 0.877)
- THCA flower In practice, all cannabis flower is THCA-rich; licensed flower is labeled by total THC
- At Lenox Hill Lab-tested flower, plus THCA diamond concentrates and diamond-infused pre-rolls
THCA vs THC
| THCA | THC | |
|---|---|---|
| What it is | The acidic form the plant makes | The form created by heat |
| Where you find it | Raw and dried flower, THCA diamonds | Heated cannabis: smoke, vapor, edibles made with decarboxylated oil |
| How it forms | Made by the plant as it grows | Forms when heat removes carbon dioxide from THCA |
| On a New York label | Counted toward total THC at 87.7% | Counted toward total THC in full |
Lab research shows THCA binds far more weakly than THC to the body's CB1 cannabinoid receptor (study), which is one reason heat matters so much in how cannabis is used.
How Heat Turns THCA Into THC
The change is called decarboxylation: heat breaks off a small carboxyl group and releases it as carbon dioxide, leaving THC behind. Lab studies find the conversion speeds up sharply as temperature rises, and that it happens within minutes at the temperatures reached when cannabis is smoked or vaporized (review, study). Edibles are made with cannabis oil that has already been heated, so their labels list THC in milligrams.