Anabolic/androgenic steroids with significant estrogenic or progestational activity may cause gynecomastia (female breast development in males). This disorder is specifically characterized by the growth of excess glandular tissue in men, due to an imbalance of male and female sex hormones in the breast. Estrogen is the primary supporter of mammary gland growth, and acts upon receptors in the breast to promote ductal epithelial hyperplasia, ductal elongation/branching, and fibroblast proliferation. Androgens, on the other hand, inhibit glandular tissue growth. High serum androgen levels and low estrogen usually prevent this tissue development in men, but it is possible in both sexes given the right hormonal environment. Gynecomastia is regarded as an unsightly side effect of anabolic/androgenic abuse by most users. In extreme cases the breast may take on a very female looking appearance, which is difficult to hide even with loose clothing.
Gynecomastia tends to develop in a series of progressive stages. The severity of this process will vary depending on the type and dose of drug(s) used, and individual sensitivity to hormones. The first sign is typically pain in the nipple area (gynecodynea). This may quickly coincide with minor swelling around the nipple area (lipomastia). This is sometimes referred to as pseudo-gynecomastia, as it primarily involves fat and not glandular tissue. At this stage, it may be possible to address mild nipple swelling by reducing or eliminating the offending steroidal compounds, and administering an appropriate anti-estrogenic medication for several weeks. If left untreated, however, this may quickly progress to clear gynecomastia, which involves significant fat, fibrous, and glandular tissue growth. The hard tissue growth may be easily felt in the early stages when pinching deeply around the nipple. Noticeable gynecomastia is likely to require corrective cosmetic surgery (male breast reduction).
Although gynecomastia is a very common side effect of steroid abuse, given its clear association with certain drugs or practices, it is also an easily avoidable one. Careful steroid selection and reasonable dosing are usually regarded as the most basic and reliable methods for preventing its onset. Many steroid users also frequently take some form of estrogen maintenance medication, which may effectively counter the effects of elevated estrogenicity. Common options include the anti-estrogen tamoxifen citrate, or an aromatase inhibitor such as anastrozole. The use of a post-cycle hormone recovery program at the conclusion of steroid administration (which usually includes several weeks of anti-estrogen use) is also commonly advised, as gynecomastia is sometimes reported in the post-cycle hormone imbalance phase when steroids are not actually being taken.
It is important to note that progesterone can also augment the stimulatory effect of estrogen on mammary tissue growth. As such, progestational drugs may be able to trigger the onset of gynecomastia in sensitive individuals, even without elevating levels of estrogen. Many anabolic steroids, particularly those derived from nandrolone, are known to exhibit strong progestational activity. While gynecomastia is not a common compliant with these drugs, they are occasionally linked to this side effect in anecdotal reports. The anti-estrogen tamoxifen citrate is usually taken in such instances, as it can offset the effects of estrogen at the receptor, which are still necessary for progestins to impart their growth- promoting effects on the breast.
Wlliam Llewellyn (2011) - Anabolics