What is THC?
THC is short for delta-9-tetrahydrocannabinol. It is the main psychoactive compound in Cannabis sativa. Psychoactive means the compound changes mood, perception, or behavior. THC causes the high linked to marijuana. Raphael Mechoulam and Yechiel Gaoni isolated THC in 1964 at Hebrew University in Jerusalem.
Chemical profile
THC has the formula C21H30O2 and a molar mass of 314.46 g/mol. It belongs to the cannabinoid class. In fresh plant material, most THC exists as THC-A, an acid form with no strong psychoactive effect. Heat removes a carboxyl group from THC-A and converts it to THC. This reaction is decarboxylation. Smoking, vaping, and baking all trigger it.
THC Edibles Dosage for Beginners: Start at 2.5 mg
How THC works in the body
THC binds two receptors in the endocannabinoid system: CB1 and CB2. CB1 receptors sit in the brain and nervous system. CB2 receptors sit in immune tissue. THC acts as a partial agonist at CB1. That action affects short-term memory, coordination, appetite, and pain signaling. Effects start within minutes after smoking and within 30 to 90 minutes after eating a dose.
THC vs CBD
THC and CBD are different cannabinoids with different actions. CBD does not produce a strong high and does not activate CB1 in the same way. Both compounds appear in cannabis plants, but in different ratios. US law defines hemp as cannabis with 0.3% or less delta-9-THC on a dry weight basis. Plants above that line are marijuana under federal law.
Legal status in the US
THC is a Schedule I substance under the federal Controlled Substances Act. Schedule I drugs have no accepted medical use and a high potential for abuse under that framework. State laws differ. Some states allow adult use, some allow medical use, and some prohibit THC. Hemp and hemp-derived products that stay at or below the 0.3% delta-9-THC limit fall outside the CSA under the 2018 Farm Bill.
The FDA has not approved cannabis as a medicine. The agency has approved drugs built on single cannabinoids: dronabinol (Marinol, Syndros) for nausea and appetite, and CBD (Epidiolex) for rare seizure disorders.
Drug tests and detection
Urine tests measure THC metabolites, with 11-nor-9-carboxy-THC (THC-COOH) as the main marker. Detection windows vary with dose, frequency of use, and body fat. A single use can show up for a few days. Heavy use can show up for weeks. Blood and saliva tests have shorter windows than urine tests.
Common forms
- Flower and pre-rolls
- Concentrates and vapes
- Edibles and drinks
- Tinctures and capsules
- Topicals
Potency is not the same across forms. A 10 mg edible and a 10 mg puff do not deliver the same dose to the body. Read the label for total THC per serving.