@temple-of-salt EONutrition on youtube has some good videos explaining the different types of thiamine. I think a B complex would be considered necessary for high dose thiamine by most people.

@Samyo Eggs have high sulfur, generally sulfur intolerance can happen because of a molybdenum deficiency. You could test and see if you have the same reaction to other high sulfur foods. Or it could be something else of course

@Samyo @tea B1 and B7 contain sulfur. I'd guess that you have a mild sulfur intolerance. Most dietary sulfur should be converted to sulfate, but if you have an overgrowth of Hydrogen Sulfide producing bacteria more sulfur would be converted to sulfite instead.

@Buck_Breaker Some people order from AlldayChemist or PharmacyDelivers from what I've heard. Although I've never used these suppliers so I can't vouch for them.