Our endo is switching my daughter because the half life of prednisone is longer than that of Cortef. She just can't remember to take the afternoon dose that Cortef requires, although she is 100% perfect about am and pm. My son (age 16) is exactly the same way, however for him the Cortef is doing what it needs to do and no switch will happen for him. I think he told me that they are both cortisol, but the prednisone is double bound. I haven't looked that one up, so I don't understand what it meant. I don't know about the saliva test. My endo did say he wanted to wait two months before doing a blood test to see how the change in meds has affected her. It seemed a little long to me.