I used to take a 150 B Forte Complex almost daily, sometimes twice daily (
https://www.chemistwarehouse.com.au/buy/124176/nature-s-own-ultra-b-150-forte-60-tablets). This contains 150mg of thiamine nitrate per pill. This supplement was so transformative for my POIS, I took it for years. I could never find another B complex that made me feel so damn good. I could never really figure out what within it was so responsible for the medicinal benefits.
I always put it's medicinal effects down to replenishing methyl donors, but now I'm not convinced thats the whole picture.
I had to stop the B complex recently because it began giving me side-effects. Just making me more apathetic/anhedonic than usual. I took this as too many methyl donors and probably running out of certain nutrients that are methyl buffers. I also got lots of bloodwork done recently, and it all showed adequate B6, high B12 and folate. So I knew my methyl donors were adequately replenished. I eat and eggs and meat very frequently as well. So I stopped taking it and felt fine for a while, until recently began noticing my mood has been really off. Taking electrolytes seemed to exascterbate the problem as well, as I had just recently switched to keto which has been a gamechanger for my libido and energy. Every time I took potassium and magnesium, my mood would become more apathetic and less motivated.
I've always seemed to have electrolyte issues even on AB, and now that I was reacting to electrolytes after 4-5 weeks of no issues, I decided to research and came across thiamine as an important nutrient for regulating electrolytes.
3 days ago I finally decided to take TTFD 100mg and am already experiencing a significant improvement in mood and energy. I don't know for sure, but I'm more bullish than ever that thiamine is really important for our condition. Not to mention all the interesting thiamine megadosing info for complex chronic diseases i.e., POTS, long-covid, etc.
I seem to also be tolerating my electrolytes better as well, but this whole thing will probably be a work in progress for a while too. In hindsight though, I think I was actually megadosing B1 (150-300mg per day) through my B complex unknowingly. That was probably providing a lot of medicinal benefit that I over attributed to methyl donors.
Basic plan at this point is to take a moderately dosed B complex vitamin maybe 1-3x per week, but thiamine daily for a while. Eventually maybe switch thiamine to every 2nd day or so. Will come to understand it all better with time.