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I first heard of 6-oxo a few years back when I was searching for PCT (post cycle therapy) for a pro-hormone I was looking at. I ended up taking the 6-oxo and it did what I needed for PCT. Helped me rebound from the pro-hormone and keep almost all my gains. Before I took the 6-oxo, I did some research and this post will be about what I found. Hopefully, it will help those looking for a natural testosterone booster or something to add to there PCT.

Sidebar: I will not be discussing any PCT questions because I am not knowledgeable enough to direct others about the best solutions. Please visit a steroid/bodybuilding forum for questions directly related to PCT. If you have questions about 6-oxo itself, ask away.

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What is 6-oxo?

6-oxo, aka Androst-4-ene,3,6,17-trione, is a naturally occurring metabolite in androgen biosynthesis. 6-oxo is found in trace amounts in some animal products. No primary source dietary source has been identified.

In humans 6-oxo has been shown to inhibit the aromatase enzyme, which is responsible for converting testosterone and other androgens into estrogen.

6-oxo is classified as a Type I inhibitor of aromatase. It works by irreversibly binding to the aromatase enzyme, preventing it from interacting with steroid hormones and producing estrogen. In layman’s terms, 6-OXO binds to the enzyme and prevents it from doing its normal function, which is to produce estrogen from androgens.

As you probably know high levels of estrogen are not what we’re looking for when trying to build muscle and get lean. High levels of estrogen can lead to negative effects such as increased body fat, water retention, man boobs (gynecomastia), reduced libido, as well as other clinical conditions best avoided.

How 6-OXO Increases Testosterone

It is thought 6-oxo raises testosterone by altering a key feedback loop in how the body regulates testosterone production. This process also keeps estrogen levels in check.

The exact mechanisms of how the body regulates testosterone levels are quite complex and will only be touched on here. Just know that it will be simplified.

It primarily involves what is called the hypothalamic-pituitary-testicular axis (HPTA), which works by overlapping negative feedback loops. Estradiol is a major player in this system. It’s about 10 times as potent as estrone and about 80 times as potent as estriol in its estrogenic effect.

Estradiol is suppressive to testosterone production. High estradiol sends the signal there is high testosterone, leading to lower test levels.

On the other hand, lower estrogen causes the body to think testosterone is low, and sends the signal to produce more test. Reducing estrogen levels is a way to fool the HPTA into ramping up testosterone through an increase in the gonadotropins: follicle stimulating hormone (FSH) and luteinizing hormone (LH).

From my research, I have only been able to find one published placebo controlled study that looked at the effects of 6-oxo in exercising adults. In the study, subjects consumed 300 mg or 600 mg daily for a duration of 8 weeks. Body composition, hormone levels, and other health markers where measured and looked at various times during and after the study.

Subjects taking 300 mg of 6-oxo experienced a 90% increase in free testosterone levels, while subjects taking 600 mg noticed 84% increase when compared to the placebo group. 300 mg users noticed 192% increase in dihyrotestosterone and 600 mg an increase of 265%. Body composition did not change significantly for either group. Neither of the 6-OXO dosages appeared to have any negative effects on clinical health markers.


Effects of eight weeks of an alleged aromatse inhibiting nutritional supplement 6-oxo on serum hormone profiles and clinical safety markers in resistance-trained, eugonadal makes. Rohle D, Wilborn C, Taylor L, Mulligan C, Kreider R, Willoughby D. J Int Soc Sports Nutr. 2007 Oct 19;4:13.


I don’t recommend 6-oxo for anyone in their teens or early twenties with a clean bill of health and who are not cycling anything. It may be useful for those struggling with issues surrounding elevated estrogen levels due to steroid use, pro hormone use, age, etc.

As seen in the study above, it did increase testosterone levels but significant body composition changes were not seen. So if you are looking to take it just to help put on muscle mass, 6-oxo will probably not be of much use to you.

If you do decide to give 6-oxo a go, supplement with between 300-600 mg per day. In the study above, their were no harsh side effects related to supplementing with 6-oxo. If you do experience any sides, discontinue use immediately (obvious I know).

You can get some up at gnc or get some off the net.