Beware the niacin flush. Once I took 500mg, after having already been accustomed to the flush. It hit hard that day though. 15 minutes after taking the pill, while driving, my vision started to narrow and go black. It felt like being chocked out. I was rapidly losing consciousness, but was able to safely pull over to the side of the road. Before completely passing out I was able to vomit up what was left of the pill. I was able to return home, and sleep for the rest of the day. This was with a single 500mg pill, after already being used to the flush.