I'm sorry to say I don't have any proof, all I know is that is what my son's Endo told me. We didn't have any warning when the 5mg cortisone acetate tablets became unavailable, and the pharmacies just kept telling us it was on back-order. We were down to the last few pills when I frantically called his Endo. That's when he gave us a prescription for the prednisone. I questioned the pharmacist about hydrocortisone & he said he thought that would have been a closer substitute than prednisone, but that the doctor must have some reason for his preference. It was some time after that when we got our computer & I found this (& other) sites and learned more about CAH & the meds. When I read that others were taking hydrosortisone, I decided to question the Endo, that's when he told me that we'd end up going through the same thing as we did with the cortisone. It's not that they don't make these meds at all, it's just that they stop making tablets in small enough doses. Sorry I can't be of more help. I can tell you that the prednisone is working fine for my son.