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How Long Does a Niacin Flush Last?

Updated on September 6, 2015

What does a niacin flush feel like?

I had been reading about all the B vitamins the night before, so while I worked I was thinking about all the benefits they offer and I couldn’t wait to buy some. When it came time for my break (I work in a supermarket) I bought a B complex and extra thiamine and niacin (B3). I took one of each and went back to work. Let the good health begin!

But something else began first. After 10 minutes had passed, I felt pins and needles in my face. Then I felt really warm. I went to the mirror. My face and neck were red and a minute later my arms were totally red, too. I was overheating and tingling all over, and my face felt slightly stiff.

Niacin is a vasodilator causing increased blood flow to the tiny blood vessels under the skin, resulting in a niacin flush – redness and warmth with possible tingling and itching.

Me after taking a niacin tablet

I didn’t want any customers to see me on account of looking like I had malaria. I tried to stay out of my supervisor’s sight, but he eventually saw me. He enquired about my health, physical and emotional, as the nature of my suffering was unclear.

I knew I had to go stand in the freezer so I came up with some work I could do in there.

The worst of the reaction lasted about an hour and a half. The all-over redness and warmth lasted the entire time. There was intermittent tingling and itching on my legs.

I didn’t realize the reaction would be so intense and would make me look ridiculous.

I had read about niacin flush so I knew what was happening. If I hadn’t been aware of it I would have thought there was something seriously wrong (maybe the vitamins were poisoned or I was allergic?), and I might have gone to the hospital.

Knowing the flush was harmless, I waited it out.

How long does niacin flush last?

I took 500 mg on an empty stomach which is why my reaction started quickly and lasted so long.

Based on what I’ve read, a dose of 50 mg is enough to cause a flush in some people.

It seems that the flush lasts between 20 minutes and 2 hours depending on the size of the dose and if it’s taken alone or with food.

I cut up my niacin tablets into fours so I could take about 125 mg at a time. I took one of them the next morning with food and didn’t experience any flushing. I took 125 mg a few more times with no reaction.

Two days later I bumped it up to 250 mg. Again, no reaction.

On the third night before bed I went to 375 mg with food. I didn’t feel anything before falling asleep. I thought I was in the clear. Then I had a dream that I was flushing and trying to find a way to cool down.

I woke up to a niacin flush. It was 3 hours later. I felt this one in my dream for about 10 minutes and after I woke up for about 20 minutes. I’m guessing this one lasted about a half hour, but I don’t know how long it was happening in my sleep. The intensity was nowhere near like it was the first time.

On the fourth night I dropped down to 250 mg to avoid flushing but, to my surprise, I reacted at this reduced dosage about a half hour after taking it.

The explanation seems to be this: My earlier doses of 250 mg were taken as two pieces of 125 mg taken separately with my food. This last dose was a single piece at 250 mg. Breaking the niacin up and spacing it by about a minute seems to have been enough to avoid the flush. I’m going to experiment further with how many smaller pieces I can take without flushing. The 375 mg on the third night was also one piece.

Experiencing my first niacin flush was interesting and I’m glad of it. I just wish it hadn’t lasted so long and that I had been home at the time.

If you are planning on experiencing a niacin flush, I suggest taking a small dose and doing it at home so you can sit in a cool bath if you want.

A "normal" niacin flush lasts 15-20 minutes with mild effects. A strong flush can last 2 hours with intense effects.

The strength of the flush depends on the dosage (50-500 mg) and whether the stomach is empty or not (food delays and seems to lessen the flush reaction).

This article is not medical or nutritional advice. It is based on my experiences and what I have read. Consult a professional before taking a dietary supplement.


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    • Howard Allen profile image

      Howard Allen 4 months ago


      There are lots of different bottles and brands available at supplement stores and grocery stores, and also online. I don't recommend any specific brand.

    • profile image

      Shieh 4 months ago

      How does the bottle look for these supplements and where can i find them???