I had to stop taking the niacin for now. I think it is responsible for my very sore boobs! Gahhh! My bra size went up very quickly and I also developed a very bad knot of muscle pain in my upper back - I don't think I was drinking enough water... I did some research on it and the breast pain and muscle pain can be quite common if you are taking too much. Rats. I really liked how it made me feel before all of that junk started happening! haha