The development of gynecomastia or feminization of the breast tissue in males is possible with anabolic steroids. This is due to an excess of estrogen being present in the body, through a process known as "aromatization" whereby androgens like testosterone are converted to estrogen. This excess estrogen then finds its way to the receptors in breast tissue and binds to them. This results in the possibility of female-like breast tissue, which must sometimes be removed by surgery. Most athletes experience itchiness of the nipples, followed by pain. Since this develops over several days, usually, the athlete has more than enough time to discontinue the use of the compounds he´s taking, or to attempt to counteract the breast tissue development while remaining on the cycle. The two most common ways to counteract gynecomastia are the use an anti-estrogen like Nolvadex or Clomiphene Citrate (best taken post-cycle) or Letrozole, a very strong Aromatase Inhibitor (AI)/anti-estrogenic compound is employed during cycle to effectively starve the growth of nourishing estrogen.
In addition to the mentioned side effects several others have been reported. In both males and females acne are frequently reported, as well as hypertrophy of sebaceous glands, increased tallow excretion, hair loss, and alopecia. There is some evidence that anabolic steroid abuse may affect the immune system, leading to a decreased effectiveness of the defense system. Steroid use decreases the glucose tolerance, while there is an increase in insulin resistance. These changes mimic Type II diabetes. These changes seem to be reversible after abstention from the drugs.