After a rather rocky start, I seem to be tolerating B1 (in the form of benfotiamine) quite well. I react very strongly to it. My energy (in between crashes) is a lot better, and I'm sleeping more soundly and going back to sleep more quickly than I have in years. Whether it will end up helping with PEM remains to be seen. When I initially tried taking B1 some months ago, it gave me a big boost of energy and then dropped me down. It was very frustrating and eventually I discovered the causes (I think). Based on Freddd's posts and my subsequent reading re refeeding syndrome, I'm just about certain the B1 caused hypophosphatemia (sort of like folate caused my potassium to tank). Much of my post-B1 fatigue went away after adding in kefir/yogurt (high in phosphorus) and a low dose of monosodium phosphate (about 750 mg.) But I was still stuck, could not get all my energy back and then theorized the B1 was depleting one of the Bs, but which one? I did not feel like experimenting, I'd reacted badly to B2 before, and then had the idea to try brewers yeast which I figured might have the B vitamins in a better ratio than my B complex. And that seems to have solved the problem. I've been on benfotiamine for about 2-1/2 weeks now, working my way up gradually from 1/4 of a 150 mg. tablet to a full 150 mg. a day (I break the tablet in half, 75 mg. twice a day) The only downside now that I can see, and I don't know its significance, is that it has raised my BP some 20 points or so. It's been up in the 140's over 80 something. It was always before 120 something over 70 something. I don't know why, but am not worrying about it. It's still a work in progress, but again, the increase in energy is amazing, although in a way I have to be more careful now not to crash when I have energy to do more things! I also take 1600 mcg. methylfolate and 5,000 mcg. sublingual methylcobalamin, plus 100 mg. B6, and a ton of other stuff, oh, and 500 mg. pantothenic acid every other day. And I think it increases my need for potassium a little, but not a lot like the folate did. So am trying to stay on top of that too!