THC-O

THC-O (THC-O-acetate, also abbreviated ATHC or THC acetate) is a synthetic prodrug of Δ⁹-THC in which the phenolic C1 hydroxyl is acetylated (C₂₃H₃₂O₃). It is not known to occur naturally in cannabis. Early synthesis was documented by the US Army's Edgewood Arsenal program in the 1970s exploring incapacitating agents. In vivo, the acetate is hydrolyzed by esterases to release free Δ⁹-THC, which accounts for its THC-like but delayed-onset subjective effects. The acetate group itself is not notably CB1-active. A 2023 case series and vape-emission analysis (Munger et al., 2024, Chemical Research in Toxicology) reported that THC-O acetate pyrolyzes to produce ketene, a potent pulmonary toxicant implicated in EVALI-like lipid pneumonia. ⚠️ Because of the ketene hazard and its unambiguously synthetic origin, many regulators classify THC-O acetate as a controlled synthetic cannabinoid. → See also: Synthetic cannabinoid, THC, Delta-8 THC.