11-OH-THC: The High that Comes from Within Us

Editor’s note (October 2026): Jason Lupoi’s 2019 explainer below is unchanged. Two things to keep in mind as you read it: the rapid, intense high in the 1973 study came from intravenous injection, not from edibles, which take an hour or more to peak; and the enzyme and potency questions he raised have since been studied directly. An addendum at the end covers what the research now shows.

It’s unsettling how much unwarranted scrutiny delta-9 tetrahydrocannabinol (THC) has generated through the years. The lucid mind should perpetually question why. These days cannabidiol (CBD) rivals THC in attention, including a recent announcement by the US Food & Drug Administration which coincidentally occurred one day prior to the confirmed expiration of US Patent 6630507B1, which regarded cannabinoids as antioxidants and neuroprotectants.

But there are, of course, other cannabinoids that deserve our attention, not in any wild, irrational ways, but as scientists and those who appreciate and want to understand Cannabis sativa, the phyto-molecules therein, and their natural metabolites. One of these metabolites is called 11-OH-Δ9-THC (spoken as eleven-hydroxy-delta-9-tetrahydrocannabinol). If you’ve eaten an edible infused with THC, you’ve already intimately become acquainted with this molecule.

Our bodies break down THC into 11-OH-THC via a process called first pass metabolism that occurs in our livers. This metabolic reaction is a part of the conversation regarding the low bioavailability of THC (said to be 4-20%). Even with the degradation of much of the orally consumed THC, we can still feel the effects of the edible long after. Thus, 11-OH-THC is intoxicating.^[1]

In fact, 11-OH-THC was first considered to be the active ingredient within cannabis.^[2] A subsequent study, however, questioned this, after the intravenous (IV) injection of 11-OH-THC failed to induce effects.^[3] Nevertheless, 11-OH-THC does intoxicate. In a 1973 study, subjects given 11-OH-THC reported a maximum high just 2-3 minutes after IV injection. The high was more intense than that experienced by smoking cannabis. Some found it initially unpleasant as their hearts beat faster, but these people later recanted, saying it was more pleasant than previous experiences from smoking.^[4] So, the effects of 11-OH-THC to the nascent user can be a little frightening early on but can segue into something demonstrably serene.

Manno et al found that just five minutes after smoking cannabis, THC measurably degraded to 11-OH-THC.^[5] But, 11-OH-THC lingers in the body much longer, which is why the overall high sustains despite potentially having a diminished “peak” high. Researchers have posited that the enzymes responsible for breaking down THC and 11-OH-THC differ.^[5] In another study, when a molecule called proadifen was used to inhibit enzymes housed in the liver, the metabolic pathway from THC to 11-OH-THC was barely affected, whereas the degradation of 11-OH-THC to downstream metabolites was more noticeably inhibited.^[6]

The scientific literature abounds with forensic methods of detecting 11-OH-THC in urine^[7] or hair.^[8] This is the realm that we find ourselves in, since until recent times, the Reefer Madness indoctrination all but squashed increasingly relevant scientific inquiry into the molecular treasure chests known as trichomes. Research, therefore, was often centered around enforcing dying laws juxtaposed to helping humankind.

But I did find one study that made me smile, like the one about the mice and the edibles did. In this study, pigeons were intravenously injected with THC or 11-OH-THC.^[9] The rate of the pigeons’ key pecking was evaluated. A 30 µg per kg of body weight dose of either cannabinoid decreased the pecking rate, but the rate returned to normal after 30 to 45 minutes. Doses of 100 or 300 µg/kg caused the pigeons to stop pecking. Recovery times ranged from 60-90 minutes and 195-240 minutes for the two doses, respectively.

It just goes to show you, though, that you can teach birds to peck keys, but once they’ve got THC or 11-OH-THC coursing through their blood, they’re no longer so controllable. What’s happening within their bird brains, however, is anyone’s guess.

Editor’s Addendum (October 2026): What Has the Research Found Since?

The enzyme question has an answer. The liver enzyme CYP2C9 does most, though not all, of the work of turning THC into 11-OH-THC. The active metabolite is then oxidized further to THC-COOH, the inactive metabolite detected in urine drug testing.^[10] CYP2C9 genetics is one reason people can respond differently to edibles. In a study of 43 volunteers given oral THC, the four participants with two copies of the slow CYP2C9*3 variant had roughly three times the THC exposure of people with the common version, and about 70 percent less THC-COOH, with a trend toward more sedation.^[11] Our endocannabinoid system pillar explains what THC and 11-OH-THC are acting on once they arrive.

The route really does change the chemistry. After smoking, 11-OH-THC in blood runs at only about 6 to 10 percent of the THC concentration, because most of the THC reaches the brain before the liver sees it. After eating, the two are roughly equal.^[10] In a study of cannabis brownies (10, 25 or 50 mg THC), blood THC and 11-OH-THC peaked at similar levels, effects began 30 to 60 minutes after eating, peaked between about 90 minutes and three hours, and lasted six to eight hours.^[12] In frequent users given the same cannabis by three routes, THC peaked at about six minutes after smoking or vaporizing and at two and a half hours after eating.^[13] That lag, rather than any simple difference in potency, is a major reason people overshoot with edibles, a theme our Measuring Cups of THC and THC overconsumption pieces take up. How much THC an edible actually delivers depends on decarboxylation during cooking, and on which THC isomer is in the product.

Is 11-OH-THC “more potent” than THC? In people, the old intravenous work found equal doses produced equal highs, with 11-OH-THC acting faster,^[10] and in the 1973 study the high and the heart-rate jump came within three to five minutes of injection versus 10 to 20 minutes for THC.^[4] The most direct modern comparison comes from mice: after accounting for blood concentrations, a 2024 study estimated that 11-OH-THC was 153 percent as active as THC in a pain test but 78 percent as active for catalepsy.^[14] Relative activity therefore depended on what was measured. No human study has repeated the comparison with modern methods. The honest summary is that 11-OH-THC is clearly active and may equal or exceed THC on some measures, but there is no single defensible potency ratio.

Two 2026 findings matter for anyone who eats cannabis and drives. In a placebo-controlled trial of 40 regular users, gummies with 10 or 20 mg THC impaired simulated driving at two and five hours after ingestion, at blood THC levels that mostly stayed below the 5 ng/mL per se limit used in several jurisdictions: only 8 of 294 blood samples exceeded it.^[15] Blood THC alone was therefore a poor proxy for impairment after edible use. First-pass metabolism and the substantial production of active 11-OH-THC may contribute to that mismatch, but the trial did not establish that 11-OH-THC caused it. Our article on whether THC and metabolite levels track impairment covers the wider problem. And “fast-acting” edibles, which claim to speed onset by encapsulating the THC, produced broadly the same impairment timeline as a standard 10 mg edible in a small crossover study still in preprint.^[16]

On testing, Lupoi’s forensic thread has moved on. THC-COOH remains the principal confirmatory metabolite in urine testing and an important marker in forensic hair analysis. In urine, it can remain detectable for days after occasional use and for weeks after heavy use; hair can reflect a much longer period.^[10] An Italian group analyzing 672 THC-positive hair samples proposed 11-OH-THC as a complementary marker of active consumption, with a tentative cutoff of 0.5 ng/mg. The researchers recommended interpreting it alongside THC-COOH rather than using it alone.^[17] Our companion piece, 11-OH-THC in Hair, covers that study and its limits.

References

1. Huestis MA. Human cannabinoid pharmacokinetics. Chemistry & Biodiversity. 2007;4(8):1770–1804.
2. Lemberger L, et al. 11-Hydroxy-Δ9-tetrahydrocannabinol: pharmacology, disposition, and metabolism of a major metabolite of marihuana in man. Science. 1972;177(4043):62–64.
3. Agurell S, et al. Pharmacokinetics and metabolism of Δ1-tetrahydrocannabinol and other cannabinoids with emphasis on man. Pharmacological Reviews. 1986;38(1):21–43.
4. Lemberger L, Martz R, Rodda B, Forney R, Rowe H. Comparative pharmacology of Δ9-tetrahydrocannabinol and its metabolite, 11-OH-Δ9-tetrahydrocannabinol. Journal of Clinical Investigation. 1973;52(10):2411–2417.
5. Manno JE, et al. Temporal indication of marijuana use can be estimated from plasma and urine concentrations of Δ9-tetrahydrocannabinol, 11-hydroxy-Δ9-tetrahydrocannabinol, and 11-nor-Δ9-tetrahydrocannabinol-9-carboxylic acid. Journal of Analytical Toxicology. 2001;25(7):538–549.
6. Gill EW, Jones G. Brain levels of Δ1-tetrahydrocannabinol and its metabolites in mice: correlation with behaviour, and the effect of the metabolic inhibitors SKF 525A and piperonyl butoxide. Biochemical Pharmacology. 1972;21:2237–2248.
7. Lowe RH, et al. Extended urinary Δ9-tetrahydrocannabinol excretion in chronic cannabis users precludes use as a biomarker of new drug exposure. Drug and Alcohol Dependence. 2009;105(1–2):24–32.
8. Wilkins D, et al. Quantitative analysis of THC, 11-OH-THC, and THCCOOH in human hair by negative ion chemical ionization mass spectrometry. Journal of Analytical Toxicology. 1995;19(6):483–491.
9. Kosersky DS, et al. Δ9-Tetrahydrocannabinol and 11-OH-Δ9-tetrahydrocannabinol: behavioral effects and tolerance development. Journal of Pharmacology and Experimental Therapeutics. 1974;189(1):61–65.
10. Huestis MA. Pharmacokinetics and metabolism of the plant cannabinoids, Δ9-tetrahydrocannabinol, cannabidiol and cannabinol. Handbook of Experimental Pharmacology. 2005;168:657–690. PMID 16596792.
11. Sachse-Seeboth C, Pfeil J, Sehrt D, et al. Interindividual variation in the pharmacokinetics of Δ9-tetrahydrocannabinol as related to genetic polymorphisms in CYP2C9. Clinical Pharmacology & Therapeutics. 2009.
12. Vandrey R, Herrmann ES, Mitchell JM, et al. Pharmacokinetic profile of oral cannabis in humans: blood and oral fluid disposition and relation to pharmacodynamic outcomes. Journal of Analytical Toxicology. 2017;41(2):83–99.
13. Newmeyer MN, Scheidweiler KB, Barnes AJ, Coffay AO, Abulseoud OA, Huestis MA. Blood cannabinoid pharmacokinetics in frequent cannabis smokers after controlled smoked, vaporized, and oral cannabis administration: markers of recent cannabis intake. American Academy of Forensic Sciences annual meeting, 2016; abstract K53.
14. Zagzoog A, Halter K, Jones AM, et al. The intoxication equivalency of 11-hydroxy-Δ9-tetrahydrocannabinol (11-OH-THC) relative to Δ9-tetrahydrocannabinol (THC). Journal of Pharmacology and Experimental Therapeutics. 2024.
15. Le Foll B, Matheson J, Antwi P, et al. Dose-dependent effects of cannabis edibles on simulated driving performance: a randomized clinical trial. JAMA Network Open. 2026;9(8):e2631306.
16. DiCecco SM, Smith E, Sturgess K, et al. Behavioral and self-report cognitive impairment differences between fast-acting, standard, and placebo cannabis edibles. Research Square preprint, May 2026 (not yet peer reviewed).
17. Casati S, Angeli I, Ravelli A, Del Fabbro M, Minoli M, Orioli M. 11-OH-THC in hair as marker of active cannabis consumption: estimating a reliable cut-off by evaluation of 672 THC-positive hair samples. Forensic Science International. 2019;304:109951.

Originally published November 30, 2019 by Jason S. Lupoi, Ph.D. Editor’s addendum and reference updates added October 2026. This article is for information only and is not medical advice.