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4-Androstene-3,6,17-trione (also marketed as "6-OXO" or 4-etioallocholen-3,6,17-trione) is a drug or nutritional supplement that may increase the testosterone-estrogen ratio. Its use can be detected in urine.[1]

4-Androstene-3,6,17-trione (4-AT) is a potent irreversible aromatase inhibitor that inhibits estrogen biosynthesis by permanently binding and inactivating aromatase in adipose and peripheral tissue. [2][3][4] Aromatase is responsible for the conversion of testosterone to estradiol. Blocking aromatase causes the body to decrease in levels of estradiol, which then results in increase of LH and consequently, testosterone. Since testosterone has myotropic activity and estradiol does not, elevated testosterone levels increase muscle mass. However, there appear to be no human or animal studies testing the hypothesis that 4-AT will produce an anabolic effect.

4-AT is also used by steroid or prohormone users to counteract estrogen level increases caused by aromatization during their steroid cycle. This helps minimize side effects such as gynecomastia but can lead to acne. Also, after a steroid cycle, the compound may be used to shorten the recovery from the testicular suppression that can be the result of the use of steroids.

A recent United States patent application claims an 88% increase in plasma testosterone levels in men, while decreasing estrogen levels by 11%.[5] The subjects took 300mg orally twice a day for four weeks without taking any other drugs or supplements.

An often-cited study (but only referenced as being authored by "a prestigious clinical research organization") claims an average 188% increase in total testosterone levels and an average 226% increase in free testosterone levels in six male participants. The subjects took 600mg a day for a total of three weeks.[6]

It appears that the "prestigious clinical research organization" was Thomas Incledon's single man company "Human Performance Specialists, Inc." . Attempts to access the Inquiries page of the research section lead to a broken link.

There are no peer-reviewed studies that evaluate the safety or efficacy of 4-AT in humans. In a warning letter dated July 7, 2006, the FDA argues that marketing of 4-AT (aka, 6-OXO) violates the Federal Food, Drug, and Cosmetic Act and as such products containing it are adulterated by legal definition.


A typical dosage regimen is 200-600mg orally once a day in the evening, for a 4-6 week cycle.


  1. J Chromatogr B Analyt Technol Biomed Life Sci. 2005 Dec 15;828(1-2):21-6 -Regarding detection of 6-OXO in urine
  2. Numazawa M, Tsuji M, Mutsumi A (1987). "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. 28(3) (Sep): 337–44. PMID 3657156.
  3. Covey DF, Hood WF. (1981). "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. 108 (4): 1597–9. PMID 7472286.
  4. Hsueh AJ, Erickson GF. (1978). "Glucocorticoid inhibition of FSH-induced estrogen production in cultured rat granulosa cells". Steroids. 32 (5): 639–48. PMID 734698.
  5. Patent application:"Use of 4-androstene-3,6,17-trione to elevate testosterone levels and the testosterone/estrogen ratio in males"
  6. Muscle & Fitness: The science of 6-OXO

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