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 . 
After that, I had a whole different outlook on the use of meds and performance enhancement. I still use NSAIDs on my own stiffness, but I won’t accept a joint injection of cortisone–it weakens the joint. I don’t give a horse Bute until the vet has seen it, and I know it’s partly a cover-up, not a cure. Nor do I work a horse that’s on Bute–it’s off work until it’s sound without Bute. If a dressage horse “needs” its hocks injected to keep doing upper-level work in collection, it needs to quit doing upper-level work in collection.
What is it? An anabolic steroid (a steroid that acts as the hormone testosterone) that occurs in small amounts in the human body.
Medical Use: Used to treat osteoporosis in postmenopausal women, to aid in the growth of blood cells in bone marrow, and to help tissue and muscle growth in people suffering from degenerative diseases like AIDS.
Athletic Use: To grow muscle mass and aid in physical recovery from workouts.
Possible Negative Side Effects: Cardiovascular damage, sexual dysfunction, liver damage, acne, sterility, baldness, enlarged prostate.
Is it legal? Available only by prescription.