The theory behind them is that they mimick androgens to enhance muscle mass. Whether or not they build muscle is up in the air, but it has been proven that they cause androgen-like side effects; i.e. hairloss, acne, gyno. My advice is to save your money, and hair, and steer clear of any pro-hormones. It would actually be safer to use a mild anabolic steroid- not to mention cheaper! If you are trying to avoid gear use, then just stick to the staples of creatine, glutamine and a well rounded diet- you won't be dissapointed!