Prednisone is a synthetic corticosteroid drug that is particularly effective as an immunosuppressant drug.It is used to treat certain inflammatory diseases (such as moderate allergic reactions) and (at higher doses) some types of cancer, but has significant adverse effects.rednisone has also been used in the treatment of migraine headaches and cluster headaches and for severe aphthous ulcer. Prednisone is used as an antitumor drug.