4-Androstene-3,6,17-trione (4-AT; 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, but has no proven effect on body composition. Its use can be detected in urine.[2][3]
4-AT is a potent irreversible
aromatase inhibitor that inhibits estrogen biosynthesis by permanently binding and inactivating aromatase in
adipose and peripheral tissue.[4][5][6]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 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.
Baylor University conducted an eight-week study to determine the effects of 300 mg or 600 mg of 4-AT in resistance-trained males. Compared to baseline, free testosterone increased by 90% for 300 mg group and 84% for 600 mg group, respectively. Also
dihydrotestosterone and the ratio of
free testosterone to
estradiol increased significantly. The report concluded that "[t]he results of this study indicate that eight weeks of 6-OXO supplementation had no effect on body composition or clinical safety markers, but incompletely inhibited aromatase activity and significantly increased endogenous DHT levels that were attenuated after a three-week washout period".[7] This study did not utilize a control group and was funded in part by two producers of commercial 4-AT.[7]
^Van Thuyne W, Van Eenoo P, Mikulcíková P, Deventer K, Delbeke FT (November 2005). "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". Biomedical Chromatography. 19 (9): 689–695.
doi:
10.1002/bmc.496.
PMID15828056.
^Deventer K, Van Eenoo P, Mikulcíková P, Van Thuyne W, Delbeke FT (December 2005). "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". Journal of Chromatography. B, Analytical Technologies in the Biomedical and Life Sciences. 828 (1–2): 21–26.
doi:
10.1016/j.jchromb.2005.08.024.
PMID16213800.
^Numazawa M, Tsuji M, Mutsumi A (September 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". Journal of Steroid Biochemistry. 28 (3): 337–344.
doi:
10.1016/0022-4731(87)91028-4.
PMID3657156.
^Covey DF, Hood WF (April 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): 1597–1599.
doi:
10.1210/endo-108-4-1597.
PMID7472286.
^Hsueh AJ, Erickson GF (December 1978). "Glucocorticoid inhibition of FSH-induced estrogen production in cultured rat granulosa cells". Steroids. 32 (5): 639–648.
doi:
10.1016/0039-128X(78)90074-0.
PMID734698.
S2CID23530490.