Some of the side effects of oral prednisone include nausea, vomiting, loss of appetite, trouble sleeping, diaphoresis, heartburn and acne, according to WebMD. Serious allergic reactions are rare, but side effects that indicate an allergic reaction include itching, swelling, rash, severe dizziness and trouble breathing.
Prednisone is a corticosteroid that decreases the immune system's response to various diseases, reducing swelling and allergic reactions, explains WebMD. Serious but unlikely side effects include an irregular heartbeat, muscle cramps, unusual weight gain, signs of infection, severe abdominal pain, slow wound healing and seizures. Prednisone can also cause blood sugar levels to rise, which can worsen diabetes.