Steroids are a type of man-made chemical that are used to mimic the effects of natural hormones. Steroids are often used to treat medical conditions and to improve athletic performance. Commonly used steroids include anabolic steroids and corticosteroids. Anabolic steroids are used to increase muscle mass and strength, as well as to improve athletic performance. Corticosteroids are used to reduce inflammation and to treat certain autoimmune diseases.