Vitamin B1 dosis?

Vitamin B1 dosis? I have read in this subreddit about vitamin b1 and said to myself why not? I don't expect anything but if it works even a little I'll be surprised. I've been told I should consume magnesium as well but I really don't know if it's going to damage my stomach or something like that. So, I need dosis, should I first take vitamin B1 only and see how it goes?