6-oxo isn’t a legal steroid, though it can have some of the effects of one. It’s a permanantly binding aromatase inhibitor. It increases testosterone by throwing the HPTA off-axis. Basically, you’ve always got a balance of testosterone and estrogen. If you have more of one, it is converted to the other. This is what causes some of the side effects of steroid abuse. Too much testosterone and your body converts the excess to estrogen, and you can get gynecomastia. 6-oxo is much like the drugs used to treat breast cancer, it binds to aromatase, the compound that converts various precursor hormones into estrogen, therefore lowering overall estrogen over time. Some of these, like Tamoxifen, only temporarily bind to the aromatase, and it is freed back into the bloodstream eventually. 6-oxo, like Letrozole, binds permanantly, and so is very effective at reducing estrogen. In response, the body produces more of the master hormones to create estrogen, but more of it is converted to testosterone instead, because of the absence of the aromatase.
Too little estrogen is not healthy, however. If you take 6-oxo, or any other anti-estrogen, don’t go nuts. You can get away with mega-dosing some supplements, but remember that this is a potent drug, and it can harm you if you don’t respect it. (Price alone keeps most folks from getting into trouble with this.)