Niacin Benefits: What Human Studies Show, Doses and Safety

Niacin (vitamin B3) is an essential nutrient, and most people in the United States already get more than they need from food. At very high supplement doses, nicotinic acid improves cholesterol and triglyceride numbers, but large randomized trials found it did not cut heart attacks, strokes or deaths, and it caused more side effects. Evidence for other uses is thinner: mostly observational studies, small trials, or results from the nicotinamide form.

Quick facts

What the human evidence shows

Deficiency: where niacin clearly helps

Severe deficiency causes pellagra, with a sun-exposed skin rash, digestive problems and neurological symptoms, and it can be fatal if untreated. The NIH Office of Dietary Supplements fact sheet says it is rare in the United States and mostly affects people with very limited diets, alcohol use disorder, certain bowel or liver conditions, or some rare disorders. The World Health Organization treats it with nicotinamide plus other B vitamins. This is established nutrition science, not a supplement benefit for people who eat normally.

Heart attacks, strokes and deaths

This is the best-studied question, and the answer is negative. A Cochrane review pooled 23 randomized trials with 39,195 people (median dose 2 g a day, median 11.5 months). Niacin did not reduce overall mortality (risk ratio 1.05, 95% CI 0.97 to 1.12), cardiovascular mortality, heart attacks or strokes. People on niacin were about twice as likely to stop treatment because of side effects (risk ratio 2.17). The authors rated the evidence moderate to high quality and concluded benefit is unlikely.

Individual trials, as summarized by the NIH fact sheet:

• Coronary Drug Project (1970s): 8,341 people who had had heart attacks, randomized to several lipid drugs or placebo, including 3,000 mg a day of nicotinic acid for an average of 6.2 years. Niacin lowered cholesterol by 9.9% and triglycerides by 26.1%, and there were fewer nonfatal heart attacks but more arrhythmias. Overall deaths did not fall during treatment. Nine years after the study ended, deaths from all causes were 11% lower in the niacin group. Limits: it is an old trial, and the drug comparison was against placebo, not modern statins.
• AIM-HIGH: 3,414 people with cardiovascular disease already on cholesterol medicine. Adding 1,500 to 2,000 mg a day of extended-release niacin lowered triglycerides and LDL and raised HDL further, but there were no fewer cardiovascular events. The trial stopped after 3 years, and there were more ischemic strokes in the niacin group. A review of the AIM-HIGH data describes the stroke excess as not statistically significant.
• HPS2-THRIVE: 25,673 adults with cardiovascular disease on a statin, given 2 g a day of extended-release niacin plus a flushing-blocking drug, or placebo, for a median of 4 years. Cholesterol numbers improved, but major vascular events did not fall, and the niacin group had more diabetes, stomach and bowel problems, bleeding and skin reactions. Limit: because niacin was paired with the flushing blocker, the extra harms cannot be assigned to niacin alone.

The fact sheet also cites a 2018 review of three trials (29,195 patients) that reported about 10% higher all-cause mortality with 1 to 3 g a day of extended-release nicotinic acid plus a statin than with a statin alone. The 2018 cholesterol guideline from the American College of Cardiology and American Heart Association says niacin may help in some cases of severe high triglycerides but has only mild LDL-lowering effects, and does not recommend it as an add-on to statins.

Why do trials study niacin on top of statins? Statins became the standard treatment, so researchers asked whether niacin added anything. In those comparisons, it did not. Nothing in these trials shows niacin as a replacement for a prescribed cholesterol medicine, and nothing here is a reason to change a medicine without your prescriber.

Cholesterol and triglycerides

This is the effect that is consistent. The NIH fact sheet says doses more than 100 times the RDA, taken for months or years, raised HDL by 10% to 30% and lowered LDL by 10% to 25%, triglycerides by 20% to 50% and lipoprotein(a) by 10% to 30%. Nicotinamide does not do this. Dietary intake is far below the pharmacologic doses used in cholesterol trials, according to the narrative review above. The key limit is that these are surrogate measures: a better number did not turn into fewer heart events. Our guide to surrogate outcomes in trials explains why that gap matters.

Does niacin clear plaque from arteries?

Some older trials of niacin combined with other drugs measured artery narrowing or artery-wall thickness, and a 2009 review by authors with extensive drug-industry ties says the trial data favor an effect on atherosclerosis. But the large outcome trials above found no drop in heart attacks or strokes, which is what clearing plaque would be expected to produce. For a long-standing plaque problem, the studied tools are medicines and lifestyle changes chosen with a clinician. Food-level niacin has not been shown to reverse plaque.

Type 2 diabetes

A meta-analysis of 8 randomized trials with 2,110 people with type 2 diabetes found niacin lowered total cholesterol, triglycerides and LDL, raised HDL, and had no significant effect on blood glucose or HbA1c. The authors called for larger, longer trials. This sits against heart-trial findings: the NIH fact sheet reports higher diabetes risk in four of the reviewed studies, and glucose rises at doses of 1.5 g a day or more. The results are mixed.

Blood pressure

A review in the International Journal of Clinical Practice found the data limited. In a small infusion study (11 people with normal pressure, 10 with hypertension), blood pressure fell in the hypertensive group (systolic up to 7 mmHg) but not in the normal group. Most long trials found no significant change, though some later analyses of large trials suggested a dose-dependent drop. The authors note that the manuscript-writing help was paid for by a drug company and that no long trial has tested blood pressure as its main outcome. Separately, a study of Chinese adults linked dietary niacin above 15.6 mg a day with new high blood pressure (reported in the 2025 review above), which is observational and unexplained.

Glaucoma

A 2024 meta-analysis of five case-control studies found people without glaucoma were more likely to report high dietary niacin intake (odds ratio 0.66, 95% CI 0.55 to 0.79 with one definition of glaucoma; 0.63, 95% CI 0.43 to 0.94 with another). This compares groups at one time and cannot show niacin prevents glaucoma; the authors point to different definitions and confounders and say randomized trials are needed.

Pregnancy

A 2021 meta-analysis of 14 case-control studies (35,743 women) found that mothers with insufficient niacin intake were slightly more likely to have babies with congenital anomalies (odds ratio 1.13, 95% CI 1.02 to 1.24). It reflects diet, not supplement trials. Ask your obstetrician about prenatal nutrition.

Nicotinamide: skin lesions and type 1 diabetes

The Linus Pauling Institute reports a phase III trial in which a pharmacologic daily dose of nicotinamide reduced precancerous skin lesions and non-melanoma skin cancers in high-risk people. It also reports that nicotinamide failed to prevent or delay type 1 diabetes in at-risk relatives. Other cancer-prevention ideas rest mostly on lab and animal work.

Why is niacin no longer recommended for the heart?

Three things came together. The trials above showed no event reduction. High doses brought side effects. And Harvard Health reports the FDA withdrew approval of niacin for use together with statins or other lipid-lowering drugs in 2016. A newer line of research is early: Cleveland Clinic researchers linked higher blood levels of a niacin breakdown product, 4PY, with heart attack and stroke risk, and 4PY caused vascular inflammation in animal models. Harvard Health notes the human part came from about 1,100 people with heart disease followed for three years, with no data on their niacin intake, so it cannot prove niacin is to blame. The lead author said the takeaway is not to cut out niacin entirely, and recommended talking with a doctor before taking over-the-counter supplements.

Doses used in studies

These are amounts researchers gave participants, not recommendations.

Is 1,000 mg a day too much? What about 500 mg, 200 mg or 100 mg?

For reference, the upper limit for supplemental niacin in adults is 35 mg a day, according to Harvard Health citing the NIH Office of Dietary Supplements. That limit is based on skin flushing and does not apply to people taking niacin under medical supervision. So 100 mg, 200 mg, 500 mg and 1,000 mg are all above it.

• 100 to 200 mg: well above the limit, and above the 30 to 50 mg where nicotinic acid typically causes flushing. The fact sheet calls flushing unpleasant rather than toxic.
• 500 mg: the fact sheet notes niacin-only supplements with 500 mg or more per serving are far above the RDA. It links liver injury to high doses taken over months or years, and says it is more likely with extended-release nicotinic acid. It gives no specific threshold at 500 mg.
• 1,000 mg and above: the fact sheet describes 1,000 to 3,000 mg a day of nicotinic acid as pharmacologic, with serious effects possible, and says doses in the thousands of mg should only be taken with medical approval and supervision. Harvard Health says high-dose nicotinamide (500 mg or more a day) can cause diarrhea, easy bruising and more bleeding from wounds.

What happens if you take niacin every day?

From food, nothing harmful has been reported. From supplements, it depends on form and dose. The NIH fact sheet and a 2025 overview of 14 reviews describe stomach upset, liver problems, flushing, rash and fatigue, which are more common at higher doses; nicotinamide causes fewer problems than niacin, and most side effects eased after the dose was lowered or stopped. At pharmacologic nicotinic acid doses, the fact sheet lists low blood pressure that can lead to falls, higher blood sugar, heartburn and abdominal pain, blurred vision, macular edema, and liver damage including hepatitis and acute liver failure.

Flushing and the bedtime question

Flushing is a vasodilation reaction: red skin on the face, arms and chest with burning, tingling and itching, which can start within 30 minutes. Taking nicotinic acid with food, building up slowly, or waiting for tolerance reduces it, according to the fact sheet. Nothing in these studies treats flushing as a benefit; in the blood pressure review, a drug that blocked the flushing pathway did not remove niacin’s blood pressure effect, so flushing is not a sign the treatment is working. The trials above compared niacin with placebo, not dose timing. For bedtime dosing, ask a pharmacist.

Niacin for women

The studies above do not report separate benefits for women. The reference intake for non-pregnant adult women is 14 mg a day (18 mg in pregnancy, 17 while breastfeeding), and the fact sheet says average intake from food and drink is 21.3 mg for women. One small study cited in the 2025 review found niacin raised glucose, insulin and C-peptide in sedentary, non-diabetic postmenopausal women.

Niacin-rich foods for vegetarians

The NIH fact sheet lists these per serving. Plant foods generally give about 2 to 5 mg, mostly as nicotinic acid, and niacin naturally bound in some grains is only about 30% usable. Enriched and fortified foods contain free niacin that is highly usable. The Daily Value is 16 mg.

Your body also makes some niacin from tryptophan in protein, at roughly 60 mg of tryptophan per 1 mg of niacin, and this varies by person.

Safety and medicine interactions

The NIH fact sheet names these interactions:

• Tuberculosis drugs (isoniazid, pyrazinamide): they interfere with the body making niacin, and pellagra can occur.
• Diabetes medicines: large doses of nicotinic acid can raise blood sugar, and people on diabetes drugs may need their glucose monitored and doses adjusted by their prescriber.
• Statins and other cholesterol drugs: in the trials above, adding niacin brought more harm than benefit.
• Blood pressure and vasoactive drugs: the Bays review notes prescription labels describe rare fainting and low blood pressure, especially with ganglionic-blocking and other vessel-active drugs.

For people who take high-dose nicotinic acid for cholesterol, the 2013 American College of Cardiology and American Heart Association guideline advises checking liver enzymes, blood sugar or HbA1c, and uric acid before treatment, during dose increases and every 6 months. It lists warning signs that call for review: raised liver enzymes, persistent high blood sugar, acute gout, unexplained abdominal pain, new atrial fibrillation, weight loss, and severe skin reactions.

Who should talk to a clinician first

• Anyone on a statin or other cholesterol medicine, diabetes medicine, tuberculosis medicine, or blood pressure medicine.
• People with liver disease, diabetes, gout, stomach ulcers or bleeding problems, kidney disease or dialysis (the 2025 overview notes kidney dysfunction limits tolerability), or eye conditions.
• People with heart disease or stroke history, who were the participants in most of the trials above.
• Anyone pregnant, planning pregnancy or breastfeeding.
• Anyone considering more than the reference intakes, which the fact sheet says should only be done with medical approval and supervision at the thousands-of-milligrams level.

What is still unknown

• Whether the 4PY finding means niacin intake causes heart disease; researchers have called for randomized trials.
• Whether niacin helps glaucoma, pregnancy outcomes or blood pressure; current evidence is observational or limited.
• Why dietary niacin above about 15.6 mg a day was linked to new hypertension in one study.
• Whether results differ by genetics or population, which the 2025 review flags as a research gap.
• How safe long-term supplement use is; the 2025 overview of reviews says side effects have not been studied systematically.

To judge claims you see for niacin, our guides on meta-analyses and systematic reviews and evaluating evidence quality explain terms like case-control, odds ratio and confidence interval used above. See also ingredient evidence versus marketing claims.

How to read a label that lists niacin

• Amount: look for milligrams (mg) and compare with the 16 mg Daily Value. Niacin may be shown as mg NE (niacin equivalents), where 1 NE is 1 mg niacin or 60 mg tryptophan. Many multivitamins sit near the Daily Value, while some niacin-only products have 500 mg or more per serving.
• Form: nicotinic acid flushes and is the form with the cholesterol effects; nicotinamide or niacinamide does not flush and does not have the cholesterol effect; inositol hexanicotinate is sold as flush-free but is absorbed less well. Extended-release, sustained-release or timed-release labels signal slower release, and the fact sheet says liver toxicity is more likely with extended-release nicotinic acid.
• Related compounds: nicotinamide riboside and NMN are not labeled as niacin sources. The fact sheet reports FDA ruled in November 2022 that NMN may not be legally marketed as a dietary supplement.
• Blends: if niacin sits inside a proprietary blend, the label may give only a total weight for the blend. Ask the maker for the per-ingredient amount and form before you take it.
• Other B vitamins: B-complex and multivitamin products add to your total, and supplement use doubled or tripled total niacin intake in national survey data, so add up everything you take.

Before you order

• Which form and how many mg per serving does the label state?
• Do you take any medicine listed above, or have a condition listed above?
• Is the product a blend that hides the niacin amount?
• Would your clinician or pharmacist check it against your medicines first?

By ClinicalStudyConnect.com Research Desk

This article is for general information purposes only and does not constitute medical advice. Consult your doctor or qualified healthcare provider before making changes to your health routine.