@Adlyfrost: In my experience any little bit of *any form* of supplemental niacin can interfere with methylation, at least when I was starting out. I tried all forms, including inositol hexanicotinate. Even really, really small amounts of niacin would cause me problems. Even a small amount of of the so-called "active" form NADH, which supposedly is symptom-free because it requires no processing in the body for the body to use it.
I have to do my B vitamins piecemeal to avoid niacin completely. I'm thinking about trying some again, however, since I'm much more stable than I used to be. We'll see.
Worth noting is that I do drink milk and eat unrefined whole grain, so it could be that I am getting enough niacin from my food and didn't need any supplemental.
But you asked was it possible and yes, IME it is possible. Plus, 75mg seems like a big dose