One study appeared to show that gw 50156 side effects included the growth of cancer cells but on further inspection, the results could be considered misleading. The study of gw1516 which was carried out on mice included 1000 times the recommended dose, taken over a prolonged period of time. As no individual would be taking such an inflated level of gw501516, there is debatable value attached to this particular study. Nevertheless, despite the criticism of this study, it was sufficient for GSK to drop the project so shouldn’t be dismissed completely.
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 . 
More specifically, the methylcobalamin form of B12 is recommended, as it has been shown to be the most effective. Taking B12 gives you a huge boost of energy while training, and more importantly, greatly helps your recovery.