THC-O, a Psychedelic Cannabinoid [Update & Warnings]

Following passage of the 2018 Farm Bill, which legalized hemp cultivation, there has been a commercial wave of products made from the legal plant. Aside from non-intoxicating CBD, which is found organically in hemp plants and can be easily extracted, there is a growing list of cannabinoids that have been manufactured by subjecting CBD to various chemical processes.

THC-O is one of the latest of those cannabinoids. It follows in the commercial footsteps of delta 8 THC and other “new” cannabinoids, which found a presence in the marketplace when manufacturers discovered how to produce them in large quantities by chemically processing CBD extracted from legal hemp plants.

In February 2023, the Drug Enforcement Administration (DEA) announced it considered THC-O an illegal synthetic cannabinoid, because THC-O is not found naturally in hemp plants. But in September 2024, the Fourth Circuit Court of Appeals ruled that THC-O is indeed a legal hemp-derived substance and falls under the Farm Bill definition of a legal cannabinoid.

What is THC-O?

THC-O is the acetate ester form of THC, sometimes called THC acetate ester, or O-acetyl-Δ9-THC. It’s usually known as THC-O acetate (or ATHC or THC-Oa) among experts, but has been shortened by almost everyone to THC-O. Sometimes people drop the hyphen and call it THCO or THC O. However you decide to spell it, it’s pronounced “THC-oh”—that’s the letter O, not a zero.

Like delta 10 THC and the other hemp-derived cannabinoids on the market, THC-O is chemically almost identical to delta 9 THC, the intoxicating compound that dominates marijuana plants. And its effects are very similar to delta 9, but because it binds more tightly to the body’s cannabinoid receptors than the other THC forms, THC-O is more intoxicating than delta 8, delta 10 or HHC—and is even stronger than delta 9 THC (more on that below).

THC-O is available in all the usual cannabis styles: vapes, oils, edibles and flower. THC-O vape carts and disposable vapes are sold with either unflavored distillate or with added terpenes for flavor. THC-O is also mixed with edible oils like MCT to make tinctures for oral use. There are THC-O edibles available too, including gummies and chocolates. Finally there is “THC-O flower,” which is simply hemp flower infused with THC-O.

What are the effects of THC-O?

As with the other hemp-derived THC variations, the big question about this one is, does THC-O get you high? The answer is a resounding yes. In fact, THC-O is purported to be 2-3 times more powerful than the delta 9 THC found in marijuana.

Measuring the effects of THC-O versus delta 8 THC, delta 10 THC or HHC is subjective, of course. But by most accounts, THC-O gets you higher than delta 8—and is a much more intense experience than all other forms of THC.

Not only is THC-O stronger than other forms of THC, but the psychoactive effects are much different. Many users describe THC-O as producing an almost psychedelic high, with borderline hallucinogenic effects. Both drug experts and sellers advise new users to go very slowly when trying this powerful cannabinoid.

There’s another reason to go slow: the effects of THC-O are always delayed. It's a so-called “prodrug,” which means that the THC-O you swallow or inhale isn’t pre-activated by heat like most THC (the process called decarboxylation). Instead, the effects of THC-O aren’t felt until it’s been fully processed through the body—just like THC edibles.

So, whether you’re eating THC-O gummies or vaping a THC-O cart, you won’t feel any effects for 20-60 minutes. Since it’s so strong, it’s important to use a small amount first, then wait and see how you react before ingesting more.

Will THC-O show up in a drug test?

There is practically no research on how the body processes THC-O. But as the acetate ester form of THC, it seems almost certain that drug tests will pick up THC metabolites in the blood, urine, or hair of a THC-O user. There is no information on how long THC-O remains in the body, but it’s safe to assume that it can be detected for at least as long as delta 9 THC—possibly for weeks or months.

The same warning applies to THC-O as delta 8, delta 10, and HHC: if your employer tests for marijuana use, it’s best to avoid THC-O.

Is THC-O safe?

THC-O is not safe to vape or smoke.

THC-O is created by chemically converting CBD into either delta 9 THC or delta 8 THC, and then converting those cannabinoids into their acetate ester form, which is called THC-O for short. The studies listed in the note at the top of this article show that when enough heat is applied to THC-O, thermal degradation can cause the formation of a dangerous lung toxicant called ketene.

The same thermal degradation process causes vitamin E acetate to generate ketene—a probable cause of the 2019 vaping lung injuries mistakenly called “EVALI” by the CDC. (Black market cannabis processors used vitamin E acetate to dilute THC oil in order to save money.)

The danger is not caused by cannabis itself, or vaping itself, but by the interaction of heat with the acetate form of various chemicals, including THC. In fact, any acetate ester subjected to heat could produce ketene.

It’s not certain if the amount of ketene produced by a vape cart is enough to create an immediate danger to the user, but it’s possible. It is also possible that cumulative lung damage could be caused by repeated small exposures.

Based on this research, we urge cannabis users to avoid vaping or smoking THC-O or any acetate form of any cannabinoid.

THC-O gummies and tinctures are not a health risk. The danger created by heating THC-O is not present in edible forms. Since there are lots of non-inhaled options available, THC-O fans should seek those instead.

Producing THC-O is definitely dangerous. Acetic anhydride is flammable, and using it creates a risk of fire and explosion. As with butane hash oil (BHO), it can only be made in properly equipped labs by people very familiar with the process. And even with experienced processors, there remains the chance that traces of the chemicals used to create THC-O could remain in the final product.

Is THC-O legal?