There are possible estrogenic side effects of Nandrolone despite it not being a very estrogenic hormone, at least not directly. Nandrolone does aromatize slightly. Aromatization refers to the conversion of testosterone to estrogen . This takes place when the testosterone hormone interacts with the aromatase enzyme. When the conversion takes place this can cause estrogen levels to go up, which can promote gynecomastia and water retention. High blood pressure can also become an issue if water retention becomes severe. Along with the low level of aromatase activity Nandrolone is also a progestin and has a strong binding affinity for the progesterone receptor. This may stimulate the mammary tissue and enhance the risk of gynecomastia in sensitive individuals.
Combating the estrogenic side effects of Nandrolone can be achieved by the use of anti-estrogen medications, specifically Aromatase Inhibitors (AI’s) such as Anastrozole ( Arimidex ). Selective Estrogen Receptor Modulators (SERM’s) are also sometimes used, such as Tamoxifen ( Nolvadex ). However, AI’s are the proper choice as they will directly reduce serum estrogen levels and SERM’s will not. An AI should be enough to reduce and avoid gynecomastia unless the individual already has existing gynecomastia that could potentially be exasperated.
Important Note: It’s often been said that Nandrolone based gynecomastia is based on increases in prolactin. It is true that 19-nor steroids can increase prolactin, which can also negatively affect libido and erection function. Some men may need to use a dopamine agonist to combat this. However, it is not prolactin that causes 19-nor based gynecomastia but rather the imbalance between estrogen and progesterone. If you merely combat prolactin you may find yourself with the very gynecomastia you tried to avoid.
Hypercalcemia may develop both spontaneously and as a result of androgen therapy in women with disseminated breast carcinoma. If it develops while on this agent, the drug should be discontinued. Caution is required in administering these agents to patients with cardiac, renal or hepatic disease. Cholestatic jaundice is associated with therapeutic use of anabolic and androgenic steroids. Edema may occur occasionally with or without congestive heart failure. Concomitant administration of adrenal steroids or ACTH may add to the edema. In children, anabolic steroid treatment may accelerate bone maturation without producing compensatory gain in linear growth. This adverse effect may result in compromised adult stature. The younger the child the greater the risk of compromising final mature height. The effect on bone maturation should be monitored by assessing bone age of the wrist and hand every six months. This drug has not been shown to be safe and effective for the enhancement of athletic performance. Because of the potential risk of serious adverse health effects, this drug should not be used for such purpose.
Heavy consumption of the essential amino acid lysine (as indicated in the treatment of cold sores) has allegedly shown false positives in some and was cited by American shotputter C. J. Hunter as the reason for his positive test, though in 2004 he admitted to a federal grand jury that he had injected nandrolone.  A possible cause of incorrect urine test results is the presence of metabolites from other AAS, though modern urinalysis can usually determine the exact AAS used by analyzing the ratio of the two remaining nandrolone metabolites. As a result of the numerous overturned verdicts, the testing procedure was reviewed by UK Sport . On October 5, 2007, three-time Olympic gold medalist for track and field Marion Jones admitted to use of the drug, and was sentenced to six months in jail for lying to a federal grand jury in 2000.