From Big cat....
It has been suggested that the estrogenic effects of oxymetholone may not be as much mediated by estrogen, as by oxymetholone itself activating the estrogen receptor. Because there is little to no aromatisation off oxymetholone, the possible progestational effect was examined first. Similar to that of nandrolone perhaps. But a study2 testing the progestational effects of oxymetholone and methandrostenolone against those of testosterone as well as nandrolone and its metabolites showed that the progestagenic activity of oxymetholone wasn't even in the neighbourhood of that of testosterone, let alone nandrolone. Ruling out the possibility of progestagenic activity and aromatisation, that only left oxymetholone engaging in a structure with the estrogen receptor itself. Since it has an A-ring similar to that of estradiol (the prime estrogen) so this would be the most logical explanation. Since progesterone acts as an estrogen agonist, it would require circulating estrogen to negotiate such levels of water build-up as oxymetholone causes, so it seemed like a far-fetched idea to begin with.