Prednisolone is a synthetic corticosteroid drug which is usually taken orally and can be used for a large number of different conditions. It has a mainly glucocorticoid effect. The related substance prednisone is a pro-drug that is converted by the liver into prednisolone, which is the active drug.

Prednisolone is particularly effective as an immunosuppressant and affects virtually all of the immune system. It can therefore be used in autoimmune diseases, inflammatory diseases (such as asthma and Crohn's disease), various kidney diseases including nephrotic syndrome and to prevent and treat rejection in organ transplantation.

Short-term side effects, as with all glucocorticoids, include high blood glucose levels, especially in patients who already have diabetes mellitus or are on other medications which increase blood glucose (such as tacrolimus), and mineralocorticoid effects such as fluid retention. Long term side effects include Cushing's syndrome, weight gain, osteoporosis, glaucoma, and type II diabetes mellitus.

Adrenal suppression occurs if prednisolone is taken for longer than 7 days, a condition which means the body is unable to synthesise natural corticosteroids and becomes dependent on the prednisolone taken by the patient. For this reason, prednisolone cannot be stopped abruptly if taken for longer than seven days, but needs to be reduced slowly; this reduction may be over a few days if the course of prednisolone was short, but may take weeks or months if the patient has been on long-term steroid treatment. Abrupt withdrawal will lead to an Addisonian crisis, which may be life-threatening.