Glossary
THC-O (THC-O-acetate)
Updated:
THC-O-acetate is a synthetic ester of THC made by reacting THC with acetic anhydride. It does not occur in the plant. When vaped, the acetate group breaks down into ketene, a toxic gas, according to 2022 laboratory work. It is excluded from the federal hemp definition.
THC-O-acetate, often shortened to THC-O, is made by taking delta-8 or delta-9 THC and adding an acetate group with acetic anhydride. The plant never makes it. Producers typically start from hemp CBD, convert it to delta-8 THC, then acetylate.
The acetate group is the problem. A 2022 study in Chemical Research in Toxicology heated cannabinoid acetates under vaping conditions and detected ketene, a highly toxic gas, in the condensate from every acetate tested, including a commercial delta-8 THC-O product bought online (Munger 2022). Ketene is the same degradant implicated in vitamin E acetate vaping harm, and toxicologists flagged THC-O as a candidate for a repeat of that outbreak (J Med Toxicol 2023).
THC-O has no natural source, so it falls squarely within the amended federal hemp definition's exclusion for cannabinoids that are not capable of being naturally produced by a Cannabis sativa L. plant, effective November 12, 2026 (7 U.S.C. 1639o). It is also a tetrahydrocannabinol derivative for total THC purposes.
No published human safety data exist for THC-O. Major carriers refuse synthetic cannabinoids outright.
Sources
- Vaping Cannabinoid Acetates Leads to Ketene Formation (Chem Res Toxicol, 2022) PubMed (accessed 2026-10-13)
- Vaping THC-O Acetate: Potential for Another EVALI Epidemic (J Med Toxicol, 2023) PubMed (accessed 2026-10-13)
- 7 U.S.C. 1639o, Definitions (hemp) Cornell Legal Information Institute (accessed 2026-10-13)