[Adam F]

DRUGS
A significant percentage of gynecomastia is caused by medications or exogenous chemicals that result in increased estrogen effect. This may occur by several mechanisms: 1) they possess intrinsic estrogen-like properties, 2) they increase endogenous estrogen production, or 3) they supply an excess of an estrogen precursor (e.g. testosterone or androstenedione) which can be aromatized to estrogen.

Contact with estrogen ******* creams, for instance, can elevate circulating estrogen levels. These may or may not be detected by standard estrogenic qualitative assays. An estrogen-containing embalming cream has been reported to cause gynecomastia in morticians.

Recreational use of *********, a phytoestrogen, has also been associated with gynecomastia. It has been suggested that digitalis causes gynecomastia due to its ability to bind to estrogen receptors.

The appearance of gynecomastia has been described in body builders and athletes after the administration of aromatizable androgens. The gynecomastia was presumably caused by an excess of circulating estrogens due to the conversion of androgens to estrogen by peripheral aromatase enzymes.

Drugs and chemicals that cause decreased testosterone levels either by causing direct testicular damage, by blocking testosterone synthesis, or by blocking androgen action can produce gynecomastia. For instance, phenothrin, a chemical component in delousing agents, possessing antiandrogenic activity, has been attributed as the cause of an epidemic of gynaecomastia among Haitian refugees in US detention centers in 1981 and 1982.

Chemotherapeutic drugs, such as alkylating agents, cause Leydig cell and germ cell damage, resulting in primary hypogonadism. Flutamide, an anti-androgen used as treatment for prostate cancer, blocks androgen action in peripheral tissues, while cimetidine blocks androgen receptors. Ketoconazole, on the other hand, can inhibit steroidogenic enzymes required for testosterone synthesis. Spironolactone causes gynecomastia by several mechanisms. Like ketoconazole, it can block androgen production by inhibiting enzymes in the testosterone synthetic pathway (i.e. 17a hydroxylase and 17-20-desmolase), but it can also block receptor-binding of testosterone and dihydrotestosterone.

In addition to decreasing testosterone levels and biologic effects, spironolactone also displaces estradiol from SHBG, increasing free estrogen levels.

Ethanol (For you Noobs: the alcohol consumed in beverages )increases the estrogen to androgen ratio and induces gynecomastia by multiple mechanisms as well. Firstly, it is associated with increased SHBG, which decreases free testosterone levels. Secondly, it increases hepatic clearance of testosterone, and thirdly, it has a direct toxic effect on the testes themselves. Unfortunately, besides the drugs stated, a multitude of others cause gynecomastia by unknown mechanisms.