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. <sup id="cite_ref-3" class="reference">
[4]</sup><sup id="cite_ref-4" class="reference">
[5]</sup><sup id="cite_ref-5" class="reference">
[6]</sup>
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%.<sup id="cite_ref-6" class="reference">
[7]</sup> The subjects took 300 mg orally twice a day for four weeks without taking any other drugs or supplements.
Baylor University conducted an eight-week study to determine the effects of 300 mg or 600 mg of 6-OXO 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. This study did not utilize a control group and was funded in part by two producers of commercial 4-AT.<sup id="cite_ref-7" class="reference">
[8]</sup><sup id="cite_ref-8" class="reference">
[9]</sup>
In a warning letter<sup class="noprint Template-Fact" title="This claim needs references to reliable sources from June 2009" style="white-space: nowrap;">[
citation needed]</sup> dated July 7, 2006, the
U.S. Food and Drug Administration (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.
On June 18, 2008,
Health Canada issued a warning that 4-AT and 6-OXO had a health risk related to blood clotting and recommended all users immediately cease use.