Nandrolone is a modification of testosterone (carbon atom removed from the 19th position) With an Anabolic/Androgenic ratio: 125:37, meaning it is highly anabolic (muscle building) and moderately androgenic (male characteristics). Due to nandrolones chemical structure it only aromatizes (converts to estrogen) slightly, at about 20% the rate of testosterone when it interacts with the aromatase enzyme. Ergo, estrogenic effects are not a major concern with its use. Of note, however, is that nandrolone is a progestin with a binding affinity of 20% to the progesterone receptor (PgR), so side effects are still possible, though rare. The development of breast tissue in males (gynecomastia) has been reported in some steroid.com users. One of the most popular anabolic steroid used in bodybuilding cycles, nandrolone is also (medically) used to treat severe debility or disease states and refractory anemias. It promotes tissue building processes, reverses catabolism (muscle destruction) and stimulates erythropoiesis (red blood cell production). This makes it a very useful drug to treat wasting disorders such as advanced H.I.V. , and also, makes it highly sought after by bodybuilders and athletes.