How long does a dose of cortef stay in your system???? My son is 7 and is given 5mg of cortef around 7:00 A.M. and 7 1/2 mg. at bedtime. Usually atleast a 12 hour span of time between the two doses. Am I doing something wrong here and what symptoms or side effects can I expect to see if his body is not getting the cortef he needs. I read further down on the message board that cortef only stays in ones body 4-6 hours.