jeeeeeez 18...your gunna fuck yourself up if you start aas now, you prob just hit puberty, your body is still growing and adjusting because your still young..My advice would be hit the gym hard everyday, have a good pre-workout, and post workout, diet is very important depending what your doing so make sure your intake protien,carbs, and cals, fats are where they are sappossed to be, and make sure your getting good/enough sleep everynight very important..HIT the books and read read read about aas youll get your answers, start it up in 2-3 years dont fuck yourself up now, you'll regret it.