SHBG and Gynecomastia: Approximately 4–10% cases of gynecomastia are due to drugs.[2] Mechanisms by which drugs cause gynecomastia include inhibition of androgen synthesis and/or metabolism (ketoconazole), antagonism at androgen receptor (flutamide, finastride), direct action at estrogen receptors by estrogen-like drugs (estrogen vaginal cream, clomiphine) and displacement of estrogen from sex hormone-binding globulin (thereby increasing the free estrogen level, e.g. spironolactone).