My experience with trying to control cortisol using supplements such as Phosphatidylserine, Theanine, Ashwagandha, Holy Basil and Relora (magnolia bark) is that they all seem to work fine, for a brief period of time, and then they will suddenly stop being effective.
I think the real root of problem, with high adrenaline and cortisol, is that they are often caused by a reaction to histamine, which in turn, is a reaction to chronic inflammation. From what I understand, high histamine with send your adrenal system into overload. I believe that trying to control cortisol or adrenaline, with supplements, is too far downstream from the root cause to be effective, hence why such supplements tend to fail in a very brief period of time.
I'm now of the opinion that inflammation is a major factor in most CFS symptoms. I think years of chronic inflammation will completely disrupt our bodies on a cellular level.
I think the best approach is to start first on a low histamine Paleo type diet, focusing anti-inflammatory foods and supplements, before moving on to other modalities. This is currently what I'm doing and although I can't say that I've made dramatic improvement, I have made improvements nonetheless.
I think that decades of poisoning our bodies with toxic food cannot just get reversed overnight. As Amy Yasko says, "it's not a sprint, it's a marathon!"