Hydrocortisone (cortisol, CortefTM) is a prescription drug. It is, however, the identical hormone to one of the naturally occurring compounds secreted by the adrenal gland cortex (outside layer) in response to stress or low blood sugar. The correct and safe use of low dose cortisol requires a doctor familiar with its administration.
By the use of oral hydrocortisone it is possible to determine if adrenal fatigue is a problem and treat it as well. This is called a therapeutic trial.This means that conventional hormone testing may not be needed when conducting a therapeutic trial, though additional information may be gained by such testing. No more than 20mg per day should be used in such a trial and the timing of a single or divided doses is important.
The best published source of information is the book, The Safe Uses of Cortisol by William McJeffries, MD. This paper-back book is more expensive than expected, and harder than average to find. If you cannot find a doctor to work with you, it would be better to buy the book rather than give up on the idea of a hydrocortisone trial if it is strongly indicated.