Quick answer

Niacin, or vitamin B3, is a B vitamin your body turns into NAD, which more than 400 enzymes need, many of them to release energy from food. Adults need 14 to 16 mg NE a day, and most get that from food. From supplements, adults should stay at or under 35 mg a day.^1,2

Key facts

Most people in the US get more niacin than they need from food: men average about 31 mg a day and women about 21 mg.¹
Nicotinic acid, one of the two main forms, can make the skin flush from about 30 mg. Nicotinamide, also called niacinamide, does not.^1,2
Amounts are given in niacin equivalents (NE), because the body also makes niacin from tryptophan, an amino acid in protein.²
Prescription niacin, at 500 to 2,000 mg a day, is a medicine taken under a doctor's care, not a supplement amount.³
Ask a pharmacist before combining niacin with a statin, a blood thinner or metformin.^3,4,5

What niacin does in the body

Every tissue turns niacin into NAD, a coenzyme that more than 400 enzymes need, more than for any other coenzyme made from a vitamin.¹

The body also has a second supply line. Tryptophan, an amino acid in protein, can be turned into niacin in the liver, which is why food tables and recommendations count niacin equivalents rather than niacin alone.^1,2

Niacin amounts are given in mg of niacin equivalents (NE). One mg NE is 1 mg of niacin or 60 mg of tryptophan.^1,2

Niacin is almost completely absorbed, even at 3 to 4 g. The liver changes any excess, and the body passes it in urine.¹

What the evidence shows

Both statements below are nutrient functions, graded moderate, with the amount they refer to. They describe what getting enough niacin does, not what extra niacin does.¹

Niacin contributes to normal energy-yielding metabolism*^1,6

Moderate evidence

A well-established nutrient function. Every tissue turns niacin into NAD, a coenzyme that more than 400 enzymes need, many of them in the reactions that move the energy in carbohydrates, fats and proteins into ATP, the cell's energy currency. 'Contributes to normal energy-yielding metabolism' is the wording European regulators permit for the B vitamins, niacin among them. It does not mean extra niacin gives more energy to someone who already gets enough.

Amount studied: Recommended intake: 16 mg NE a day for men and 14 mg NE for women, from food and supplements combined

Niacin is needed for the normal development and function of the body's cells*^1,2

Moderate evidence

NIH describes niacin as important for the development and function of the cells in the body. Besides its role in energy, the NAD made from niacin is used by enzymes that control which genes are active and pass signals inside cells, and NADP keeps the cell's antioxidant systems working. The statement is about getting enough niacin, which most people in the US do from food.

Amount studied: Recommended intake: 16 mg NE a day for men and 14 mg NE for women, from food and supplements combined

Skin creams with niacinamide are a separate topic. The sources on this page are about niacin you eat or swallow.

How much you need

Men need 16 mg NE of niacin a day from food and supplements combined.^1,2

Women need 14 mg NE a day, 18 mg NE during pregnancy and 17 mg NE while breastfeeding.^1,2

Food covers this for most people. In national survey data, only about 1% of US adults took in less than the average requirement from food and drink alone.¹

Some supplements that contain only niacin provide 500 mg or more per serving, far above the recommended amount.¹

The dosage guide sets out the amounts for every age, with the upper limits beside them.

Forms of niacin

Nicotinic acid is one of the two main forms of niacin in supplements, and the form used in prescription niacin. Taken beyond nutritional needs, it can make the skin flush.^1,2

Nicotinamide, also called niacinamide, is the other main form. Its slightly different structure means it does not cause flushing, and it has fewer side effects than nicotinic acid.^1,2

Inositol hexanicotinate is often labeled 'flush free'. It does not cause flushing, but on average about 30% less niacin is absorbed from it than from nicotinic acid or nicotinamide, which are almost completely absorbed.¹

Some nicotinic acid products are made as prolonged, sustained, extended or timed release to lessen flushing. The prescription label warns that equal doses of different release types are not interchangeable.^1,3

A Supplement Facts panel that lists only 'niacin' may not say which form it holds. Nicotinamide is often printed as niacinamide.

Food sources

Poultry, beef, pork and fish provide about 5 to 10 mg of niacin per serving, mostly as NAD and NADP, forms the body uses well.^1,2

Many breads, breakfast cereals and infant formulas in the US have added niacin. Added niacin is in a free form that is well absorbed.^1,2

Peanuts, brown rice and other plant foods add smaller amounts, and protein adds more through tryptophan. The food guide lists the amounts per serving.¹

What's in ours

What’s in ours

Men's Multi: Niacin, 30 mg NE per serving, from the label

The Men's Multi label lists niacin 'as Niacin' and does not name the form. If it is nicotinic acid, its 30 mg NE sits at the level where NIH says flushing can begin, and close to the 35 mg upper limit for supplements.^1,2

Side effects, medicines, and who should ask first

Nicotinic acid at 30 to 50 mg or more often causes flushing: the skin of the face, arms and chest turns red and can burn, tingle and itch. It usually passes and is considered unpleasant rather than toxic.^1,2

High doses of nicotinic acid taken for months or years can harm the liver, from raised liver enzymes to hepatitis and liver failure. This is more likely with extended-release forms, and severe cases have followed switching from immediate-release to sustained-release niacin at the same dose.^1,3

The upper limit for niacin from supplements and medicines is 35 mg a day for adults, including during pregnancy and breastfeeding. It is 30 mg for ages 14 to 18, 20 mg at 9 to 13, 15 mg at 4 to 8 and 10 mg at 1 to 3. It is set at the level linked to flushing, covers both nicotinic acid and nicotinamide, does not count niacin in food, and does not apply to people taking niacin under medical supervision.^1,2

Ask your pharmacist or doctor first

Myopathy and rhabdomyolysis, muscle damage that can be severe, have been reported when statins were combined with niacin at 1 g a day or more. The labels of prescription niacin, atorvastatin, rosuvastatin and simvastatin all describe this, and the simvastatin label advises against the combination at that dose in Chinese patients. NIH says experts do not recommend high doses of nicotinic acid for people taking a statin.^2,3,4,7,8

On the medicine's label

Ask your pharmacist or doctor first

The prescription niacin label reports small, dose-related drops in platelet count and rises in prothrombin time, a clotting test, and advises caution and close monitoring of both in people taking anticoagulants. NIH notes that nicotinamide at 500 mg a day or more can cause easy bruising and more bleeding from wounds.^2,3

On the medicine's label

Your doctor may want to check on you

The metformin label lists nicotinic acid among drugs that tend to raise blood sugar and may lead to loss of blood sugar control, and advises close watching when such a drug is started or stopped. NIH says nicotinic acid at 1.5 g a day or more is most likely to raise blood sugar, and that people taking diabetes medicines may need their doses adjusted.^1,2,5

On the medicine's label

Ask your pharmacist or doctor first

The prescription niacin label says niacin may add to the effects of ganglionic blocking agents and vasoactive drugs, such as nitrates, calcium channel blockers and adrenergic blockers, and cause a drop in blood pressure on standing. Its leaflet tells people who take blood pressure medicines to get up slowly if flushing wakes them at night.³

On the medicine's label

NIH also notes that isoniazid and pyrazinamide, medicines for tuberculosis, lower niacin levels. Bile acid binding resins such as cholestyramine and colestipol bind niacin, and the prescription label says the two must be taken hours apart, so ask your pharmacist how to space them.^1,2,3,9

Ask your doctor first if you have liver disease, a stomach ulcer, gout, diabetes or a bleeding problem⁹
Ask first if you take prescription niacin: its label says supplements with large amounts of niacin or nicotinamide can add to its side effects³
Ask first if you are pregnant or breastfeeding, or if the supplement is for someone under 19, whose upper limit is lower¹
Add up the niacin in every product you take, including multivitamins and B complex products

Questions people ask

What does niacin do for your skin?

Like every tissue, skin needs the NAD made from niacin. The sources we use do not show that extra niacin changes the skin of people who already get enough, and creams with niacinamide are a separate topic not covered here.¹

Is niacin the same as niacinamide?

Niacinamide, also called nicotinamide, is one form of niacin. The other main form is nicotinic acid. Both count as niacin on a label, but only nicotinic acid causes the flush.¹

What does niacin do for men?

The same as for women: the roles under 'What the evidence shows' apply to everyone. Men need slightly more, 16 mg NE a day against 14 mg NE for women, and on average get about 31 mg from food.^1,2

Why does niacin make my skin red and itchy?

That is the niacin flush. Nicotinic acid widens small blood vessels in the skin, often within 30 minutes of a dose of 30 mg or more. It is unpleasant rather than toxic and usually passes, but see a doctor if it comes with dizziness or a rash.^1,2

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Sources

*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.

This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.