Steroid use

Hi i dont know if anyone here can help me but my older brother smokes a lot of Marijuana and now he is about to start using steroids to get inshape. I am worried that he is gonna do serious damage to his body but i cant find anything online about what will happen when the to drugs mix. If someone can tell me what will happen to him or where i could find this information i would greatly appreciate it. I dont want to see my brother or his friend get hurt.