Anabolic and androgenic steroids are available as prescription medications to be used in cases in which the body does not make enough hormone and supplementation may be required. Some hormone supplements in this pathway include growth hormone and testosterone itself. These medications are legally prescribed by health-care providers, but this group of drugs is often used illegally and abused to help increase athletic performance and improve body appearance. When used in a well-nourished body, anabolic steroids will cause weight gain primarily due to an increase in muscle mass.
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 .