Whew... the flush! If you are unprepared for the flush, read up about it FIRST or it will be quite disconcerting. The first time I took this product, I forgot completely that I added it to my morning vitamin mix and then I skipped a few days because I forgot. So Monday morning, I am at work and I take my vitamins with my morning tea, and all of a sudden I start feeling WEIRD... VERY weird. It starts with prickling in your nostrils, that spreads to your cheeks, then ears, which get very hot, then down the neck through your torso and out to your fingers and toes. It is like standing inside the sun... OMG. So I am looking at my secretary who tells me I look a little odd, like I am "pink". Heat is rolling off me in waves I cannot believe she can't feel it from 10 feet away. I AM the sun... My socks are clearly melting around my feet. I contemplate whether I should be worried as this is really very strange, then I start to process the sensations, and consider whether I am having a heart attack ... probably not, pulse is fine, or a stroke... probably not, as I am cogent, just HOT. I wrack my brain thinking I am having an allergic reaction but I haven't eaten anything yet today. So then I remember... OH... The Niacin. I read the reviews, I remembered the "flush". Well, that term does not accurately describe this sensation. It subsides after about 25-30 minutes but lessened some after 15 or so. Whew. That was my fault. So after thinking about it, that wasn't so bad, just different. You can feel that niacin working, coursing through your body. Oh, don't forget the distinctly metallic taste that floods your mouth while this is happening. Now, after a couple of weeks, it seems the flush is diminishing a little but I have decided that I kind of like it. So just be prepared when you try it for the first time if you are not accustomed to this sensation. The product itself is great, I would purchase again.