cut and paste from Johns Hopkins web site:
Prednisone is a corticosteroid. In contrast to anabolic steroids (used by “bodybuilders”), corticosteroids are used in inflammatory conditions for their anti–inflammatory effects. They have a rapid onset of action, and profoundly affect many parts of the immune system as well as most other body systems. Corticosteroids are a cornerstone of treating most types of vasculitis, and are often used in combination with other immunosuppressive medications
Furthermore, prednisone is highly catabolic.