THC-O acetate (THC acetate, THC-O) is a semi-synthetic cannabinoid made by chemically reacting THC with acetic anhydride. It does not occur in the cannabis plant. In the UK, it is a Class B drug: the Misuse of Drugs Act 1971 controls esters of THC, and THC-O is one. Research on its effects in people is almost non-existent, and heating it may release a toxic gas called ketene.
Key facts
- Other names
- THC-O, THCO-acetate, THC-O-A, THC acetate ester
- Type
- Semi-synthetic cannabinoid: an acetate ester of THC (delta-8 or delta-9)
- Formula
- C23H32O3
- Natural?
- No. It is made in a laboratory by acetylating THC with acetic anhydride.
- UK status
- As of October 2026, controlled as Class B under the Misuse of Drugs Act 1971 (esters of controlled cannabinol derivatives)
- Main safety concern
- Cannabinoid acetates may form ketene, a lung toxicant, when heated or vaped
What is THC-O acetate?
THC-O acetate is THC with an acetate group attached to its phenol (OH) group. Chemists call this acetylation, and it turns THC into an ester. The "O" in THC-O refers to the oxygen atom where the acetate group binds. The same change can be made to delta-8 THC, delta-9 THC, HHC and even CBD, which is why researchers talk about a whole family of "cannabinoid acetates".
THC-O is not a natural cannabinoid. Analysts preparing reference standards make it by reacting THC with acetic anhydride (Holt et al., 2022). It belongs to the group the UK's Advisory Council on the Misuse of Drugs (ACMD) calls semi-synthetic cannabinoids.
How is THC-O different from THC?
| THC-O acetate | Delta-9 THC | Delta-8 THC | |
|---|---|---|---|
| Formula | C23H32O3 | C21H30O2 | C21H30O2 |
| Origin | Synthetic step (acetylation) | Main natural cannabinoid of drug-type cannabis | Commercial products are made by converting other cannabinoids |
| Human research | Almost none | Extensive | Limited |
| UK status (October 2026) | Class B | Class B | Class B |
Acetate versions of cannabinoids appear to work as "prodrugs". In laboratory tests, HHC-O acetate, a close relative, is inactive and needs to be broken down by enzymes in the body to release the active compound (ACMD, 2025). This may explain why users describe a slower onset.
What are THC-O effects?
There are no controlled studies of THC-O effects in people. What exists is mostly online reports. A 2023 study analysed posts in a Reddit forum about THC-O from 2021. It found discussion of variable product content, comparisons with other substances, claims of psychedelic effects, and concerns and bad experiences. Most users heated and inhaled it (Kruger et al., 2023).
A forensic report from the US described products labelled as delta-8 THC or THC acetate that were linked to a case of visual and auditory hallucinations. The products contained THC-O acetates and CBD di-acetate, and the authors note that minimal clinical or pharmacological data exist for these compounds (Holt et al., 2022).
Is THC-O safe?
Its safety has not been studied. Two concerns stand out:
- Ketene: as an acetate ester, THC-O may break down when heated and release ketene gas, which is toxic to the lungs (Kruger et al., 2023). Ketene has been suggested as a factor in the US outbreak of vaping lung injury (EVALI) linked to vitamin E acetate. The ACMD notes that amounts formed from cannabinoid acetates appear low and that no EVALI cases have been linked to them so far (ACMD, 2025).
- Unknown content: products are often mixtures. In the forensic case above, a single product held several different acetates (Holt et al., 2022).
Is THC-O legal in the UK?
No. The Misuse of Drugs Act 1971 controls "cannabinol derivatives", which include THC, as Class B drugs. Paragraph 2 of Part II of Schedule 2 extends that control to esters and ethers of these derivatives, so THC acetate is controlled as well (ACMD, 2025). This is different from HHC, whose hexahydro structure is not covered by the same wording. See our guide to HHC.
Other countries have acted too. Japan, for example, introduced specific controls on delta-8 and delta-9 THC-O in March 2023 (ACMD, 2025).
Does THC-O show up on a drug test?
Very likely, because the body converts acetates back into the parent compound. In Swedish forensic work, cannabis screening tests cross-reacted with semi-synthetic cannabinoids, including acetates, before confirmation tests identified them (ACMD, 2025). For CBD products and testing, see CBD, drug tests and driving.
From our production
We don't sell HHC or any other cannabinoid that intoxicates, and we don't sell THCA products that turn into THC when heated.
— Robin Roy Krigslund-Hansen, co-founder and CEO
Frequently asked questions
What is THC acetate?
THC acetate (THC-O acetate or THC-O) is THC that has been chemically reacted with acetic anhydride, which adds an acetate group. It does not occur naturally and is classed as a semi-synthetic cannabinoid.
What does THC 0 mean?
"THC 0" is a common misspelling of THC-O. The letter O stands for the oxygen atom where the acetate group attaches. It has nothing to do with zero THC.
Is THC-O stronger than THC?
That claim comes from user reports, not from controlled studies. There are no clinical data comparing THC-O with THC in people.
Is THC-O legal in the UK?
No. THC-O is an ester of THC, and the Misuse of Drugs Act 1971 controls esters of THC as Class B drugs.
Is it safe to vape THC-O?
Its safety has not been studied. Cannabinoid acetates may form ketene, a lung toxicant, when heated, although the amounts appear low.
Does Formula Swiss sell THC-O?
No. We don't sell THC-O or any other intoxicating cannabinoid.
Related guides
Formula Swiss does not sell THC-O. Our CBD oils are sold as cosmetics for use on the skin and are not intended to diagnose, treat, cure or prevent any disease. This article is general information about the science and the law, not legal or medical advice.
Last reviewed:
Sources
- Advisory Council on the Misuse of Drugs (ACMD). Semi-synthetic cannabinoids: cannabinoids related to tetrahydro-cannabinol and cannabidiol. GOV.UK, May 2025.
- Holt AK, Poklis JL, Peace MR. Δ8-THC, THC-O acetates and CBD-di-O acetate: emerging synthetic cannabinoids found in commercially sold plant material and gummy edibles. Journal of Analytical Toxicology 2022. doi:10.1093/jat/bkac036
- Kruger DJ, et al. A content analysis of social media discussions on THC-O-acetate. Cannabis 2023. doi:10.26828/cannabis/2023/000164
