I'm fluent on vitamin B1 for hours but it starts to wear off after hours

I'm fluent on vitamin B1 for hours but it starts to wear off after hours I started a Magnesium + vitamin B1 treatment about 18 months ago. It's effective to +95% fluency. One thing I have noticed is that if I talk too much in one setting for two hours or more, the fluency is starts to go away pretty noticeably and I'd have to refuel. I have experienced it several times after speaking with my friends or having a long interview where I do most of the talking. I think my brains burns all the vitamin B1 in my body when I do that.