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.

Blocking aromatase causes the body to decrease in levels of estradiol, which then results in increase of LH and consequently, testosterone.

However, there appear to be no human or animal studies testing the hypothesis that 4-AT will produce an anabolic effect.

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] In a FDA Warning Letter[citation needed] dated July 7, 2006, the U.S. Food and Drug Administration (FDA) argues that marketing of 4-AT violates the Federal Food, Drug, and Cosmetic Act and as such products containing it are adulterated by legal definition.