The most commonly used AAS in medicine are testosterone and its various esters (but most commonly testosterone undecanoate , testosterone enanthate , testosterone cypionate , and testosterone propionate ),  nandrolone esters (most commonly nandrolone decanoate and nandrolone phenylpropionate ), stanozolol , and metandienone (methandrostenolone).  Others also available and used commonly but to a lesser extent include methyltestosterone , oxandrolone , mesterolone , and oxymetholone , as well as drostanolone propionate , metenolone (methylandrostenolone), and fluoxymesterone .  Dihydrotestosterone (DHT; androstanolone, stanolone) and its esters are also notable, although they are not widely used in medicine.  Boldenone undecylenate and trenbolone acetate are used in veterinary medicine . 
As a non-aromatizing androgen, dihydrotestosterone is extremely potent. Aromatization refers to the conversion of testosterone or anabolic steroids into estrogen. High estrogenic activity causes bloating, acne, water retention and oily skin. As dihydrotestosterone does not aromatize even at high dosages, users do not face the aforementioned side-effects. Lack of water retention also has a hardening effect on muscle tissue, in bodybuilders. Being a powerful androgen, dihydrotestosterone is also responsible for a shift in the estrogen-testosterone ratio in the body. Due to its predominant androgenic component, the steroid has a stimulating effect on the adreno-pituitary functions, and causes neurological excitation in the ‘sexual orientation areas of the brain’. This in turn, spikes sex drive in males.