Delta-9-Tetrahydrocannabinol

Occurrence: Delta-9 is activated THCa. While Delta-9 does occur naturally on the plant, this is in small amounts. When a user smokes the plant, the THCa converts to Delta-9-THC. Smoking Delta-9-THC does not do any other conversions, and may even destroy the molecule.

Psychoactive: Yes - The primary reason you get high. Secondary is CBN and the Entourage Effect of terpenes/cannabinoids.

Effects: You get high! If eaten, the liver converts this into 11-hydroxy-THC, which is about 10 times the potency.

Potency: Depends on dosage, presence of terpenes, and presence of cannabinoids.

Discovery: 1941

Note: - Keep in mind, Delta-9 is NOT what is on Cannabis. THCa is on Cannabis, and only when smoked does it become Delta-9. This is why you cannot just eat a nug to get high.