I have a lot of experience with this. I took thiamine and magnesium for about 3 years. I’m now completely off it. In my experience, it seemed to help after the first few days. After a while (a few weeks), I started to notice more bad days creeping in, to the point it felt like the supplements weren’t actually helping. I continued taking them though in case it was helping, even if marginally so. Recently, my stuttering has become more severe, so I decided to stop taking them because I felt it was no longer helping at all, and I didn’t want to continue spending $20 or so a month on supplements. I think a lot of it might be placebo, or maybe just a minor reduction in block severity. I think quality of sleep, stress levels, and attitude play a much larger role in the severity of your stutter. If I had to put a number on it, I’d say the thiamine protocol maybe gave me a 5% reduction in severity, but not consistently over time.