I take 200 mg. thiamine HCL daily - I've taken it for several years. I started with 100 mg, gradually worked up to 300 mg and then eventually backed down to 200 mg. I also take a good methyl B complex, methylfolate, methylcobalamin, B2, B6 and a ton of other stuff.
When I first took B1 maybe 8 years ago, I started with 100 mg. and it gave me an amazing boost in energy which was quickly followed a day or 2 later by severe fatigue so I had to stop it. It took a long time to figure out that the B1 had caused my phosphorous to tank, causing the fatigue, due to a refeeding syndrome reaction. So when I finally retried the B1 over a year later, and had the same reaction, I drank several glasses of kefir (high in phosphorous) and sure enough, within a few hours the fatigue started to go away. I've taken B1 ever since, and have had to supplement with phosphorous ever since.
methylfolate caused the same reaction, energy boost followed by severe fatigue, only the methylfolate caused my potassium to tank - which was quickly remedied because I had been reading Freddd's posts about methylation and potassium. And I've had to take potassium daily ever since.