Some of us have wondered why initial positive results boomeranged with higher doses, that perhaps it could be depletion of some nutrient, mineral or other vitamin. Usual suspects: other b vitamins (too much of one depletes others). Unusual suspect: manganese (I read in an old Mindell book about supplements that manganese worked with thiamine to produce an enzyme that aids thyroxin production). Note: I'm hypothyroid and crashed with excess thiamine and wonder if others that crashed suffer from low thyroid as well? Shot in the dark suspects: low zinc and/or copper. Only mention these as I have trouble balancing the two, seemed to get worse with extra thiamine. Anyone have other suspects? Or comments about those mentioned above?