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 . 
These latest miraculous gains by Thibaudeau are a little contradictory because, while he’s said repeatedly on their forum that he could get much bigger if he wanted to, he’s also been saying that he doesn’t want to/can’t because of health issues (and I believe he also said that he only took steroids experiementally for a little while when he was a teenager). He clearly must have changed his mind, however, because he’s just claimed to have gained more muscle in 6 weeks than many drug-free bodybuilders of his stature gain in a lifetime of training. He’s doing very well – he’s now carrying over 40 pounds more muscle than the world’s best drug-free bodybuilding champions of his height (which is also well over twice as much muscle as they’ve managed to build).