Corticosteroids (steroids) are medicines that are used to treat many chronic diseases. Corticosteroids are very good at reducing inflammation (swelling) and mucus production in the airways of the lungs. They also help other quick-relief medicines work better. The steroids (corticosteroids) used to treat chronic lung diseases are not the same as anabolic steroids, used illegally by some athletes for bodybuilding. Corticosteroids do not affect the liver or cause sterility.