6-OXO is the trade name of a supplement whose active ingredient is androst-4-ene-3,6,17-trione, a synthetic steroid that is androstenedione with an extra ketone (oxygen) group at carbon 6. In lab studies with human placental tissue it is a “suicide substrate” of aromatase, the enzyme that turns androgens into estrogens: the enzyme processes it and is permanently inactivated in the process. It was sold in the US as a “nutritional” aromatase inhibitor meant to raise testosterone (Deventer et al., J Chromatogr B 2005).

The most important fact: only one published human trial has tested it. That 8-week study of 16 men had no placebo group, was funded by supplement companies, and found higher free testosterone and DHT but no change in body composition, while estrogens did not fall (Rohle et al., J Int Soc Sports Nutr 2007). It has never been an approved drug, it is banned in sport, and regulators in the US and Canada have acted against products containing it.

This page summarizes what the laboratory research, the single human trial and regulators report. It is for education only and is not medical advice.

Property	Detail
Class	Synthetic steroidal aromatase inhibitor (androstenedione derivative)
Chemical name	Androst-4-ene-3,6,17-trione (6-oxoandrostenedione); C₁₉H₂₄O₃, 300.4 g/mol; CAS 2243-06-3
Medical approval	None; never an FDA-approved drug
Route studied in humans	Oral capsules
Doses used in the human trial	300 mg/day or 600 mg/day for 8 weeks
Half-life	Not established in humans; parent drug detectable in urine for about 24 h, main metabolite up to 37 h
Key mechanism fact	Irreversible (“suicide”) aromatase inactivation in placental microsomes
US controlled-substance status	Not named in 21 CFR 1308.13 (its saturated relative 5α-androstan-3,6,17-trione is)
WADA status	Prohibited at all times (S4.1 aromatase inhibitors, named explicitly; Specified Substance)

What it is

Androst-4-ene-3,6,17-trione has the formula C₁₉H₂₄O₃ and a molecular weight of 300.4 g/mol (PubChem). Structurally it is androstenedione, the natural precursor of testosterone and estrone, with a ketone added at carbon 6 of the B-ring. Researchers often call it 6-oxoandrostenedione or “AT.”

Despite the similar names, it is a different compound from adrenosterone (“11-OXO”), which carries its extra ketone at carbon 11 and acts as an androgen precursor rather than an aromatase inhibitor. It is also distinct from androstenedione itself, which aromatase converts into estrone.

6-OXO was not invented as a supplement. It was a research tool in aromatase biochemistry for decades: rat studies used it to block aromatization as early as 1978 (Booth, J Endocrinol 1978). By 2005 it was being sold online as a supplement called “6-OXO” (Deventer et al., 2005), made by ErgoPharm / Proviant Technologies of Champaign, Illinois (Health Canada 2008).

How it inactivates aromatase

Aromatase normally removes carbon 19 of androstenedione through three oxidation steps, producing estrone. Lab work with human placental microsomes (cell fractions that contain the enzyme) showed the following for 6-OXO:

Finding	Study
Binds aromatase with an apparent Ki (inhibition constant) of 0.43 µM and causes a time-dependent loss of enzyme activity, not just competitive blocking	Covey & Hood, Endocrinology 1981
Binds irreversibly to the enzyme, probably through a sulfur atom, in a time-dependent way that requires NADPH	Numazawa et al., J Steroid Biochem 1987
Inactivation runs through a 19-oxo intermediate; a 4β,5β-epoxy-19-oxo derivative acts as the reactive species that bonds to the active site	Numazawa et al., Biochem Pharmacol 1996
Part of the drug is still aromatized, to 6-oxoestrone, through the same 19-hydroxy and 19-aldehyde steps used for androstenedione	Numazawa et al., J Steroid Biochem Mol Biol 2007

Among prescription drugs, the closest relative is the steroidal aromatase inhibitor exemestane; anastrozole and letrozole are nonsteroidal (Goss et al., J Clin Oncol 2013). Unlike those drugs, 6-OXO has no clinical trials showing how much it lowers estrogen in people.

The 1987 study also found that placental microsomes rapidly convert 6-OXO into a 3β-reduced metabolite, which is itself a weaker irreversible aromatase inhibitor (Ki 6.5 µM) (Numazawa et al., 1987). All of these findings come from test-tube enzyme systems, not from people.

How it works in the body

Human pharmacokinetic data are limited to doping-control studies at Ghent University, in which volunteers took the 6-OXO supplement and their urine was analyzed:

Measure	Finding	Study
Urinary products	Parent drug plus androst-4-ene-6α-ol-3,17-dione (major metabolite) and androst-4-ene-6α,17β-diol-3-one (minor)	Deventer et al., 2005
Form in urine	Parent drug mostly conjugated; both metabolites only as conjugates	Deventer et al., 2005
Detection window after the manufacturer’s recommended dose	Parent drug and the 6α,17β-diol metabolite: 24 h; the 6α-ol-3,17-dione metabolite: up to 37 h	Van Thuyne et al., Biomed Chromatogr 2005

No study has reported its blood half-life, oral bioavailability or blood levels in humans.

Regulatory status

6-OXO has never been approved as a medicine anywhere we could find. Its status as a supplement has been challenged in several ways.

United States: controlled substances

The DEA Schedule III list of anabolic steroids names 5α-androstan-3,6,17-trione, the fully saturated relative of 6-OXO (no double bond between carbons 4 and 5). It does not name androst-4-ene-3,6,17-trione itself (21 CFR 1308.13). 5α-Androstan-3,6,17-trione was added to the statutory definition of “anabolic steroid” by the Designer Anabolic Steroid Control Act of 2014 (Pub. L. 113-260) (21 U.S.C. 802).

The same 2014 law added a catch-all clause. An unlisted substance that is derived from, or structurally “substantially similar” to, a listed anabolic steroid is treated as an anabolic steroid if it was made with the intent to promote muscle growth or testosterone-like effects, or is marketed that way (21 U.S.C. 802(41)(C)). Whether 6-OXO falls under that clause depends on how a product is made and promoted; we found no DEA rule or ruling that addresses 6-OXO by name. It should therefore not be described as a named Schedule III substance.

United States: supplement law

On May 11, 2009, FDA announced that a federal court consent decree had condemned about $1.3 million of bodybuilding products from LG Sciences for destruction (FDA seizures and injunctions list). According to the announcement, FDA testing found that one product, Formadrol Extreme XL, contained 1,4,6-androstatriene-3,17-dione (ATD) and “3,6,17-androstenetrione (also known as 6-OXO)” (announcement text, New Hope 2009).

FDA’s legal basis was that the products contained unapproved food additives and/or new dietary ingredients without adequate information that they do not pose a significant or unreasonable risk. FDA also stated that it had no scientific information on the safety of the products or their ingredients.

Canada

In June 2008 Health Canada told consumers not to use 6-OXO or 1-AD (1-androstenediol), both made by ErgoPharm / Proviant Technologies. It called 6-OXO “an unauthorized natural health product in Canada” and also warned against other products containing 4-androstene-3,6,17-trione (Health Canada 2008).

Sport

The WADA 2026 Prohibited List names “4-Androstene-3,6,17 trione (6-oxo)” under S4.1 aromatase inhibitors, prohibited in and out of competition. S4.1 substances are Specified Substances. Arimistane (androsta-3,5-diene-7,17-dione) and androstatrienedione (ATD) are listed in the same class.

What the research shows

Hormones in trained men (Rohle et al. 2007)

The only published human trial gave 16 resistance-trained, healthy men (mean age 26.6 years) either 300 mg/day or 600 mg/day of 6-OXO (ErgoPharm) for 8 weeks, followed by a 3-week washout (Rohle et al., 2007). The 300 mg dose was split 100 mg in the morning and 200 mg in the evening; the 600 mg dose was split 300 mg and 300 mg. Assignment to dose was random and double-blind, but there was no placebo group: the authors decided one was not needed because they did not measure performance.

Changes compared with each group’s own baseline:

Measure	300 mg/day	600 mg/day	Comment
Free testosterone	+90% overall	+84% overall	Significant at weeks 1, 3 and 8
DHT	+192% overall	+265% overall	Significant at weeks 1, 3 and 8
Free testosterone/estradiol ratio	+53%	+67%	Significant
Estrone	+22%	+52%	Rose rather than fell
Estradiol	+27%	+12%	Not significant; did not fall
Total testosterone	Trend only	Trend only	p = 0.062
Body fat, fat-free mass, body weight (DEXA)	No change	No change	No significant effect

The two doses did not differ significantly from each other on any hormone, and all values returned to baseline after the 3-week washout. The authors concluded that 6-OXO “did not completely inhibit aromatase activity” in the doses tested. Because estrogens did not decrease, the rise in androgens cannot be clearly explained by aromatase inhibition.

Limits of this trial to keep in mind:

No placebo or untreated control, so changes over time cannot be separated from assay drift, season or chance.
Very small: 8 men per dose.
Industry funding: the study was supported by a grant from Proviant Laboratories (Champaign, Illinois) and InStone Nutrition (Aliso Viejo, California). Health Canada names ErgoPharm / Proviant Technologies of Champaign as the maker of 6-OXO.
Questionable lab values: several reported numbers are far outside usual human ranges in both groups at baseline (for example, FSH of 0.03–0.2 mIU/mL, estradiol reported in “ng/mL,” and serum total protein near 10 g/dL), which suggests assay or reporting problems.

The same Baylor group earlier tested Novedex XT, a different supplement that the Rohle paper describes as containing a 6-oxo-androstene THP-ether plus 3,17-diketo-androst-1,4,6-triene (ATD). In that 8-week placebo-controlled trial of 16 young men, total testosterone rose 283%, free testosterone 625% and DHT 566%, and fat mass fell 3.5% (Willoughby et al., Int J Sport Nutr Exerc Metab 2007). These results apply to that product, not to 6-OXO itself. A 2024 systematic review of “testosterone boosters” rated that non-hormonal aromatase inhibitor product only “possibly effective” for male athletes (Morgado et al., Int J Impot Res 2024).

What has not been studied

There are no trials of 6-OXO in women, older men, men with low testosterone, or in any disease. There are no data on muscle strength, performance or long-term safety, and no head-to-head comparisons with prescription aromatase inhibitors.

Side effects and risks

What the trial reported

In the Rohle trial, participants reported no side effects, and the authors found no significant changes in blood counts, liver and kidney chemistry, lipids, urinalysis, heart rate or blood pressure over 8 weeks (Rohle et al., 2007). With only 16 men, no control group and the lab-value problems noted above, this cannot establish safety.

Regulator safety signal

Health Canada reported one Canadian case in which a man with no known predisposing conditions developed seizures and blood clots in the brain associated with using 6-OXO together with 1-AD (Health Canada 2008). Because two products were taken together, the event cannot be attributed to 6-OXO alone.

Unknowns

FDA stated in 2009 that it had no scientific information on the safety of products containing 6-OXO. Effects of long-term estrogen suppression in men (for example on bone and lipids) are documented for prescription aromatase inhibitors on their own pages, but have not been measured for 6-OXO. Product content is also uncertain: FDA’s 2009 action involved 6-OXO found in a product alongside a second aromatase-inhibiting steroid (ATD).

Athletes

Because it is named on the WADA list, any detectable use is an anti-doping rule violation. Its metabolites can be detected in urine for at least 37 hours after a single recommended dose (Van Thuyne et al., 2005).

Key takeaways

An irreversible aromatase inhibitor in the lab. In placental enzyme studies, 6-OXO permanently inactivates aromatase. Like exemestane it is a steroid, but unlike exemestane it has no clinical data on estrogen lowering.
One small, uncontrolled human trial. In 16 men taking 300 or 600 mg/day for 8 weeks, free testosterone and DHT rose, but estrogens did not fall and body composition did not change.
Safety is unproven. The trial reported no side effects, but it was too small and too flawed to show safety; Health Canada logged a serious case with 6-OXO taken alongside another product.
Not a named controlled substance, but challenged as a supplement. It is absent from the DEA Schedule III list (its saturated relative is listed). FDA treated a product containing it as having unapproved food additives or new dietary ingredients, and Health Canada called it unauthorized.
Banned in sport. WADA names it under S4.1 aromatase inhibitors, prohibited at all times.

Sources

Rohle D, Wilborn C, Taylor L, Mulligan C, Kreider R, Willoughby D. Effects of eight weeks of an alleged aromatase inhibiting nutritional supplement 6-OXO (androst-4-ene-3,6,17-trione) on serum hormone profiles and clinical safety markers in resistance-trained, eugonadal males. J Int Soc Sports Nutr. 2007;4:13. PubMed.
Deventer K, Van Eenoo P, Mikulcíková P, Van Thuyne W, Delbeke FT. Quantitative analysis of androst-4-ene-3,6,17-trione and metabolites in human urine after the administration of a food supplement by liquid chromatography/ion trap-mass spectrometry. J Chromatogr B Analyt Technol Biomed Life Sci. 2005;828(1-2):21–26. PubMed.
Van Thuyne W, Van Eenoo P, Mikulcíková P, Deventer K, Delbeke FT. Detection of androst-4-ene-3,6,17-trione (6-OXO) and its metabolites in urine by gas chromatography-mass spectrometry in relation to doping analysis. Biomed Chromatogr. 2005;19(9):689–695. PubMed.
Covey DF, Hood WF. Enzyme-generated intermediates derived from 4-androstene-3,6,17-trione and 1,4,6-androstatriene-3,17-dione cause a time-dependent decrease in human placental aromatase activity. Endocrinology. 1981;108(4):1597–1599. PubMed.
Numazawa M, Tsuji M, Mutsumi A. Studies on aromatase inhibition with 4-androstene-3,6,17-trione: its 3 beta-reduction and time-dependent irreversible binding to aromatase with human placental microsomes. J Steroid Biochem. 1987;28(3):337–344. PubMed.
Numazawa M, Mutsumi A, Tachibana M. Mechanism for aromatase inactivation by a suicide substrate, androst-4-ene-3,6,17-trione. The 4 beta, 5 beta-epoxy-19-oxo derivative as a reactive electrophile irreversibly binding to the active site. Biochem Pharmacol. 1996;52(8):1253–1259. PubMed.
Numazawa M, Takahashi M, Nagaoka M, Handa W, Yamashita K. Mass spectrometric analysis of oxygenations in aromatization of androst-4-ene-3,6,17-trione, a suicide substrate of aromatase, by placental microsomes. Isotope effect and stereochemistry. J Steroid Biochem Mol Biol. 2007;107(3-5):220–227. PubMed.
Booth JE. Effects of the aromatization inhibitor androst-4-ene-3,6,17-trione on sexual differentiation induced by testosterone in the neonatally castrated rat. J Endocrinol. 1978;79(1):69–76. PubMed.
Willoughby DS, Wilborn C, Taylor L, Campbell W. Eight weeks of aromatase inhibition using the nutritional supplement Novedex XT: effects in young, eugonadal men. Int J Sport Nutr Exerc Metab. 2007;17(1):92–108. PubMed.
Goss PE, Ingle JN, Pritchard KI, et al. Exemestane versus anastrozole in postmenopausal women with early breast cancer: NCIC CTG MA.27–a randomized controlled phase III trial. J Clin Oncol. 2013;31(11):1398–1404. PubMed.
Morgado A, Tsampoukas G, Sokolakis I, et al. Do “testosterone boosters” really increase serum total testosterone? A systematic review. Int J Impot Res. 2024;36(4):348–364. PubMed.
National Center for Biotechnology Information. PubChem Compound Summary for CID 150986, androst-4-ene-3,6,17-trione. PubChem.
Drug Enforcement Administration. Schedules of controlled substances: Schedule III, paragraph (f), anabolic steroids. 21 CFR 1308.13. eCFR.
21 U.S.C. 802(41), definition of “anabolic steroid,” as amended by the Designer Anabolic Steroid Control Act of 2014 (Pub. L. 113-260). govinfo.
World Anti-Doping Agency. The 2026 Prohibited List, S4.1 Aromatase inhibitors. WADA.
Health Canada. Health Canada warns consumers not to use the dietary supplements 6-OXO and 1-AD due to potential serious health risks. June 2008. Government of Canada.
Food and Drug Administration. Dietary supplements worth $1.3 million condemned and forfeited to the United States under consent decree. May 11, 2009. Listed at FDA; announcement text reproduced by New Hope.

6-OXO (Androst-4-ene-3,6,17-trione)