steroids as said are used to stimulate your testosterone levelswithin your body to give you the required bulk. Down sides are that they will make you retain water to give you bulk, give you acne, high blood pressure and kidney/ liver problems.
Anabolic steroids are used widely within medicine for ailments such as AIDS, Anorexia, Bolemia, muscular sclerosis (sp) etc etc as they are a muscle building drug that helps such diseases.
Personally I don't know whether it's worth the risks unless you are a serious body builder who competes etc.