Adrenal fatigue is likely inaccurate; low free cortisol may be due to rapid degradation or conversion to cortisone, not low total cortisol production.

“There's a term that you hear thrown around a lot called adrenal fatigue the suggestion is that if a person feels lousy it's because their adrenal gland isn't making enough cortisol because it's fatigued and of course these people may indeed have low levels of cortisol they may even have low levels of free cortisol but doesn't mean their adrenal glands are fatigued I would say the answer is in most cases probably not in fact in most of those patients if you look at the total metabolized amount of cortisol and cortisone you would in fact see that they have ample amounts of production what might be happening is that they are degrading too much of their cortisol and or turning too much of their cortisol into the inactive Cortisone and instead of maybe converting it back actually just metabolizing it here”