Fludrocortisone is a corticosteroid. It works by causing the kidneys to retain sodium and acting as a replacement for cortisone when the body does not produce enough.Carry an ID card at all times that says you take fludrocortisone. Tell your doctor or dentist that you take fludrocortisone before you receive any medical or dental care, emergency care, or surgery.Fludrocortisone may cause an increase in blood pressure, salt and water retention, and calcium and potassium loss. Talk with your doctor to see if you need to decrease the amount of salt in your diet or take a calcium or vitamin D supplement. Check with your doctor if any of these most common side effects persist or become bothersome:Difficulty sleeping; dizziness or lightheadedness; headache; increased appetite; increased sweating; indigestion; nervousness