When raw THCa is heated, it is converted to THC through the decarboxylation process. The simplified answer is through heat and light or the decarboxylation process. Heat removes a carboxylic acid group from THCA, altering the chemical structure of THC. This makes it perfectly shaped to adapt to our endocannabinoid system (ECS) and the CB1 receptors that run through our central nervous system, allowing us to enjoy that classic elevated experience.
There are very few psychoactive benefits of freshly harvested cannabis flowers until decarbonization occurs. The decarboxylation process basically activates the acid conversion switch, converting them into THC and CBD. The heating process transforms THCA, the inactive psychoactive compounds, into THC, producing intoxicating effects. In addition, it takes inactive cannabidiol acid (CBDA) and converts it into CBD, which has milder effects than THC.
The importance of heating is well understood and is one of the foundations of cannabis pharmacology. The cannabinoid acids found in the plant's resin glands contain an additional carboxyl molecule that makes them psychoactively inert. These molecules must be removed through a heating process known as decarboxylation. Through this process, THCA is converted to THC, CBDA into CBD, etc.
Interestingly, a cured cannabis flower actually contains very little THC until the heating process is complete, so the test data that patients see in dispensaries technically reflect the expected THC content, rather than real. The raw cannabis flower contains the acidic cannabinoid THCA, which acts as a “precursor” to THC. That acid contains an additional carboxyl molecule that blocks the psychoactive effect. Decarboxation eliminates that additional carboxyl group and THCA is transformed into THC due to prolonged exposure of the raw flower to high temperatures.
Several studies have confirmed that a temperature range of 220 to 240°F is ideal for converting THCA to THC. If you smoke, cook, drink or vape cannabis, you should look for products with a high amount of THCA. While the FDA doesn't specifically mention THCA, it's best to avoid these products in states where THC hasn't been legalized.