6-oxo and clomid/nolva work differently. 6-oxo is an aromatase inhibitor similar to formestane and arimidex. These compounds work by preventing test to convert (aromatize) into estrogen. Clomid/Nolva are estrogen blockers. They bind to estrogen receptors to prevent estrogen from doing the same. Although 6-oxo and clo/nolva are used for PCT, personally, i prefer to use 6-oxo during cycle to prevent bloat/gyno (similar to arimidex and formestane) and clo/nolva for post. I just never understood the value of an aromatase inhibitor during post since little to no aromatization is taking place, maybe someone can school me on the subject if i'm off base. That said, I believe that for PCT, clo/nolva is the way to go.