Regarding prolactin, androgens decrease prolactin levels whereas estrogens increase prolactin. Non-aromatizing androgens have never been shown to elevate prolactin levels in humans, but testosterone has, due to its aromatization to estradiol (19). Prolactin secreting tumors, or prolactinomas, are often associated with gyno. But in these cases the prolactin is believed to induce gyno by suppressing testosterone production: “Prolactinomas that are sufficiently large to cause gynecomastia do so as a result of impairment of gonadotropin secretion and secondary hypogonadism”. (20). However, this is a moot issue in AAS users whose gonadotropin secretion is already blunted.
According to research cited in (20), prolactin may have a direct stimulatory effect on mammary tissue development, but only in the presence of high estrogen levels:
The presence of mild hyperprolactinaemia is therefore not uncommon in patients with estrogen excess. Significant primary hyperprolactinaemia, on the other hand, may directly stimulate epithelial cell proliferation in an estrogen-primed breast, causing epithelial cell proliferation and gynaecomastia.
So rather than focusing solely on lowering prolactin levels which may be elevated in users of aromatizing androgens, attacking estrogen should be the first line of action.