Steroids can have long-lasting and sometimes irreversible side effects on the body. Anabolic steroids have been linked to increased cholesterol, stroke and blood clots, urinary and bowel problems, and problems with the musculoskeletal system. Since steroids are a hormone, much like testosterone, the effects on sex characteristics can be far reaching, causing a kind of hyper-masculinity in young men. They can also cause male-pattern baldness and shrinking of the testicles. The excess of testosterone can also have feminizing effects on young men, such as breast development. (Jerry Adler, 2004)
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.