THCa

THCa, or Tetrahydrocannabinolic Acid, is the precursor to Delta 9 THC. By itself, it does not produce the psychoactive "high" associated with THC. But, it has been shown to have a range of potential therapeutic benefits as well as psychoactive effects when exposed to heat. 

THCa is the same as THC on the molecular level except that THCa has an extra carboxyl ring. This extra carboxyl ring prevents THCa from being psychoactive when ingested. When exposed to heat, the process known as decarboxylation rids the molecule of the extra carboxyl ring and it converts to THC.

Once the THCa has been heated or smoked, it becomes THC and provides similar effects.

You may be wondering, how is this legal? According to the 2018 Farm Bill, as long as products contain less than 0.3% Delta 9 THC by dry weight, hemp-derived products are legal. So, THCa flower could contain a very high percentage of THCa, as long as the Delta 9 THC is less than the 0.3% threshold.