Be aware that fat soluble form may lead to toxicity long-term since it's stored in fat. If you will continue using B1 it would be probably better to switch to thiamine hcl which is water soluble form. I read about it a lot (articles, comments, pdf, lot od googling) and almost everytime they suggest water soluble form and you can go up to 1200mg per day (higher dose will not give you better effect, body will pee it out) and even 5000-7000mg dosages were mentioned to mot being toxic (maybe long-term they will, but that dose is useless anyway). What form of magnesium are you using? Are you avoiding foods high in tannins that blocks B1 absorption? btw for me it didn't work, I hope you will have more luck with B1 than me :)