According to Uptodate- Endicrinology section many treatments are in fact effective for treating Gynecomastia:
There are three types of medical therapy: androgens, antiestrogens and aromatase inhibitors. Unfortunately, most of the studies of medical therapy for gynecomastia had small sample sizes, were unblinded, or were uncontrolled.
Androgens — A number of different androgen preparations have been evaluated in the treatment of gynecomastia, although none are FDA-approved for this purpose. Testosterone, when given as a long-acting ester parenterally, has not been more effective than placebo and may exacerbate the gynecomastia because the exogenous testosterone is aromatized to estradiol [8], and the usual doses are probably somewhat more than physiologic. However, testosterone replacement therapy has been shown to reduce the prevalence of gynecomastia in patients with cirrhosis [10]. The effect of transdermally administered testosterone on gynecomastia has not been reported. The nonaromatizable androgen, dihydrotestosterone, has been used percutaneously. One report noted a reduction in breast volume in 75 percent of the patients and complete resolution in approximately 25 percent [11]; there were no side effects and the decrease in breast tenderness occurred within one to two weeks. Injections of dihydrotestosterone also demonstrated improvement in gynecomastia in a small number of subjects [12]. Danazol, an androgenic progestin, has been evaluated in a single placebo-controlled study [13]. 23 percent of the patients receiving danazol had complete resolution in contrast to only 12 percent of those receiving placebo [13]. Danazol appeared to be safe and well-tolerated, but it is known to be associated with edema, weight gain, acne, nausea, and muscle cramps when used for other conditions.
Antiestrogens — Both clomiphene and tamoxifen have been evaluated in the treatment of gynecomastia. Response rates of 36 to 95 percent have been reported with clomiphene. However, two major studies of pubertal gynecomastia found a much lower incidence of benefit: fewer than one-half of patients had more than a 20 percent decrease in breast volume or were satisfied with the results [14,15].
Two randomized double-blind studies with a total of 16 patients have been carried out with tamoxifen in doses of 10 mg orally twice a day. Neither study reported a complete remission, but there was a statistically significant reduction in pain and breast size [16,17]. Complete response rates of 50 and 80 percent have been noted in two uncontrolled trials [18,19]. Most patients who received tamoxifen for up to four months did not experience any side effects, although rarely epigastric distress and nausea have been noted.
A restrospective review of patients with persistent pubertal gynecomastia who received either raloxifene (n = 10) or tamoxifen (n = 15) reported a decrease in gynecomastia in 12 of 14 breasts (86 percent) and 20 of 22 (91 percent) breasts in the raloxifene and tamoxifen groups, respectively. More patients in the raloxifene group experienced a 50 percent reduction in the breast glandular tissue (86 versus 41 percent in the raloxifene and tamoxifen groups, respectively). However, only 3 of the 10 patients in the raloxifene group and one of the 15 patients in the tamoxifen group had complete resolution of the gynecomastia in both breasts. Forty percent of the patients in each group were not satisified with the results and underwent surgical removal of the tissue [20].
Aromatase inhibitors — Testolactone, an aromatase inhibitor, has been evaluated in an uncontrolled trial in a small number of boys with pubertal gynecomastia; there was an average 40 percent decrease in breast size, but the authors did not report the number who had a complete remission [21]. Thus, there is insufficient information to recommend testolactone as an initial therapy for gynecomastia, Although on theoretical grounds it would seem reasonable to use this drug or one of the newer aromatase inhibitors, such as anastrozole, letrozole, or formestane [22], a double-blind, placebo controlled trial of anastrozole treatment for pubertal gynecomastia failed to show any beneficial effect over placebo [23].
Recommendation — In view of its possible efficacy and low incidence of side effects, I usually recommend a three month trial of tamoxifen for patients with painful gynecomastia before referring the patient for surgical removal of the breast tissue.