I think this is a critical point...in my personal experience, people metabolize all drugs differently. Rarely do we know how our body actually metabolizes anything. Some people metabolize very slowly and others metabolize very quickly, and then there is the whole absorption issue which affects the effective dosage.
It's frustrating since so many of us here are lacking a good expert doctor in CFS/ME and it seems there is a lot of self-treatment going on, especially with vitamins and other supplements, myself included.
It is frustrating. Even if you have the best doctor in the world, haven't we learned how complicated the body is and how little is really known about it? No one is ready for these modern, environmental diseases. And many times, the damage is done, there's only so much you can do. Or is there?
I always think about the example of copper and zinc and how they need to be in balance. Most people are low in zinc so everyone is told to take zinc, but what if you have low copper? It seems like some with ME/CFS have low copper, I did. If you take too much zinc and no copper, it will through the balance off.
So there is a danger is supplementing, willy-nilly, but on the other hand, you have to do something, if you take no vitamins, that's not good either. You know your own body...or do you? And what about the reactions that feel bad but are actually good? How can you tell the difference between a bad reaction that's bad and a bad reaction that's good because it's causing the needed changes or the needed detox? Or is the detox bad because the body can't handle it and the toxins, like metals, will resettle causing more damage? What if the only doctor that takes insurance is not the best or has you take drugs? I can't handle drugs at all. They really mess me up. And I wish doctors would collaborate. Several good ones together are better than one alone.
My naturopath/nutritionist had me take so many tests and helped me a lot but he didn't use standard process supplements and I found that those helped me immensely. He started me off on what I need--how else would I have known that my spleen and thymus were weak and he had me take spleen and thymus glandular but it wasn't until I took Immuplex from Standard Process which has liver, bone, spleen and thymus PMGs that I really saw an improvement. And he didn't know about Rich's methylation protocol, which also helped me immensely.
He also taught me that there's an order to healing. Certain things you have to fix first, such as gut problems, metal problems, hormone problems, after you fix certain problems, only then do you work on the immune problems, then supplementing, etc. I notice that's a mistake a lot of people make is throwing a bunch of things at the problems out of order.