Niacin (vitamin B3)
An essential B vitamin, sold as niacin or nicotinamide, best known for skin.
- Sun-damaged skin
- Eyes and vision
- Weight and BMI
- Flushing
A plain-English overview, not advice. Written from published reviews and trials and from what people say in public forums.
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On this page
What is niacin (vitamin B3)?
Vitamin B3 is an essential nutrient, and going short of it has a name: pellagra, the old deficiency disease of the skin, the gut and the mind. It comes from food - fish, meat, grains and dairy - and the body can also build it from the amino acid tryptophan. On a UK shelf it appears under two quite different names: niacin, which chemists call nicotinic acid, and niacinamide, which the research calls nicotinamide. Both are raw material for NAD+, a coenzyme every cell uses, which is why one vitamin turns up in conversations about skin, eyes and energy alike.
Why do people take niacin (vitamin B3)?
Sun-damaged skin
The thinking. Nicotinamide is the form people reach for with their skin in mind, usually after a lifetime of sun. The thinking is that it refills the cell’s NAD+ pool, which powers the repair of damage done by ultraviolet light and steadies the skin’s inflammatory response. The trials used 500 mg twice a day.
What research has found. Trials counted new skin lesions in adults who had already had two or more skin cancers. In one trial of 386 such adults, new ones appeared about a fifth less often over a year than on placebo, and a review of 29 trials covering 3,039 people pointed the same way. A later trial of 158 people taking anti-rejection medicines after a transplant found no difference between the groups. Studies here point in different directions, so this one is still being worked out; the dose, how long people took it and who took part all seem to matter.
Eyes and vision
The thinking. Nicotinamide has been taken up by people with glaucoma, and a recent review notes that use is rising. The thinking is that the retinal cells carrying signals from eye to brain work under metabolic strain, that NAD+ is what keeps their energy chemistry going, and that blood levels of nicotinamide tend to be lower in people who have glaucoma.
What research has found. Two crossover trials, in people whose eye pressure was already being lowered, gave one to three grams a day for six to twelve weeks and measured the retina’s electrical response: it rose further on nicotinamide than on placebo in both. Visual field tests, which measure what a person can actually see, showed no difference. A review of eight human studies called them small and short. The studies disagree, so this is unsettled: dose, duration and who took part all seem to shift the result.
Weight and BMI
The thinking. Vitamin B3 sits in the chemistry that turns food into usable energy, which is why it appears in supplements aimed at weight and metabolism. The thinking comes largely from animal work, where raising NAD+ levels changed the way fat and sugar were handled and slowed weight gain on a rich diet.
What research has found. One review pooled 22 treatment arms and 5,144 people taking nicotinic acid or nicotinamide. Average BMI came out slightly lower than in the control groups, by about a fifth of a BMI point, with more change at higher doses, while body weight itself did not shift; of the two hormones measured, one rose and one did not. Results here go both ways, which usually means the dose, the length of a trial or the group taking part makes the difference.
Flushing and tolerability
The thinking. Whether they will flush is the first thing many people want to know before buying. Flushing is a widening of the small blood vessels near the skin, and it goes far more with nicotinic acid than with nicotinamide, which is why a third form, labelled no-flush, sits on the shelf beside them.
What research has found. An overview of 14 reviews set out what was recorded: stomach upset, changes in liver blood tests, flushing, rash and tiredness, more often at higher doses, less often with nicotinamide than with niacin, and mostly easing when the dose was cut or stopped. A meta-analysis of 47 studies covering 11,741 people found major effects in healthy adults on nicotinic acid alone at doses below 1,000 mg a day, and argued that the upper limits in force, 35 mg a day in the United States and 10 mg in Europe, may be conservative. Studies here point in different directions, so this one is still being worked out; the dose, how long people took it and who took part all seem to matter.
What does niacin (vitamin B3) do in the body?
Vitamin B3 is not a fuel in itself. It is the raw material for NAD+, a coenzyme every cell uses, and cells build their supply from niacin, from nicotinamide, or from the amino acid tryptophan. NAD+ and its relatives run through more or less every reaction that turns food into energy.
NAD+ does more than energy work. It is also spent by the enzymes that repair DNA, adjust which genes are active and keep the daily body clock, so a cell busy repairing itself uses it up; levels fall as people age, which is the thread running through much of the newer research. Nicotinic acid has a second job that nicotinamide does not: it docks onto a receptor on the cell surface called HCAR2, and that is where its effects on blood fats and on immune responses are thought to begin.
What do people say about taking niacin (vitamin B3)?
These are anecdotes people have shared, not evidence.
What people like
- Very commonly, those who kept going say the flush faded within a week or two of regular doses and stopped bothering them.
- A few describe rather enjoying the warmth and the redness once they knew what it was, reading it as blood moving.
- Some report no trouble at all with the amide form, or with the small amounts carried in an ordinary multivitamin.
- A minority taking larger daily amounts for their blood fats say they simply got used to it and carried on for years.
Common complaints
- Very commonly the first flush frightened people: burning, bright red blotchy skin and itching that nobody had warned them to expect.
- Several describe it as sunburn-like, with stinging, burning ears or a rash over arms, neck and legs, lasting about an hour.
- Some report stomach upset, dizziness or an itchy throat alongside the flush, and a minority stopped taking it there and then.
- A recurring story is an accidental large dose stacked up from a multivitamin, a protein powder and fortified yeast flakes together.
How people take it
- The daily amounts described run from about 100 mg to two grams, the larger ones usually taken with blood fats in mind.
- Very commonly people split the dose and take it with or after food, building up slowly rather than starting at full strength.
- Several say they take it before bed, after a low-fat meal, so that any flush happens while they are asleep.
- Others switch to the amide form or a slow-release one, and a few say they take an aspirin first or avoid hot drinks.
Read from these public discussions:
- To tell you about niacin (Mumsnet, 2021)
- Niacin flush (AnandTech forums, 2006)
- OMG Niacin SUCKS!!! (Quit smoking aid) (AnandTech forums, 2004)
- Niacin (Vitamin B3) Nasty Flush/Rash (AnandTech forums, 2008)
What forms of niacin (vitamin B3) are there?
| Form | What’s different | Per serving, on products we list |
|---|---|---|
| Niacin (nicotinic acid) | Nicotinic acid, the acid form, and the one most associated with flushing at higher doses. | not in our price tables yet |
| Niacinamide | The amide form, called nicotinamide in research, and the one used in the skin and eye trials. | 250 mg |
| Inositol hexanicotinate (no-flush) | Inositol carrying six nicotinic acid units; labels call it no-flush or flush-free. | not in our price tables yet |
What else is worth knowing about niacin (vitamin B3)?
- Labels give the vitamin B3 per serving, and a serving may be more than one tablet; the form is named as niacin or nicotinic acid, as niacinamide or nicotinamide, or as inositol hexanicotinate.
- The amounts used in the trials are well above what a food-level supplement carries: 500 mg twice a day in the skin trials, one to three grams a day in the eye trials.
- Much of the older niacin research used one to two grams a day in people under medical care for their blood fats, often alongside a statin, which is a different setting from a shelf tablet.
- One review of long-term high-dose nicotinamide raises questions about its effect on the body’s methyl chemistry.
If you take medication, are pregnant, or have a health condition, check with a pharmacist or GP first.
The research behind this page (17 studies)
- The Role of Nicotinamide as Chemo-Preventive Agent in NMSCs: A Systematic Review and Meta-Analysis. (2023, meta-analysis)
- Effect of Nicotinamide in Skin Cancer and Actinic Keratoses Chemoprophylaxis, and Adverse Effects Related to Nicotinamide: A Systematic Review and Meta-Analysis. (2022, meta-analysis)
- Nicotinamide for Skin-Cancer Chemoprevention in Transplant Recipients. (2023, randomised trial)
- Prevention of non-melanoma skin cancers with nicotinamide in transplant recipients: a case-control study. (2017, randomised trial)
- A Phase 3 Randomized Trial of Nicotinamide for Skin-Cancer Chemoprevention. (2015, randomised trial)
- Nicotinamide Supplementation in Glaucoma: A Systematic Review of Human Studies. (2026, systematic review)
- Effects of nicotinamide supplementation in normal-tension glaucoma: a crossover placebo-controlled randomised clinical trial. (2026, randomised trial)
- Improvement in inner retinal function in glaucoma with nicotinamide (vitamin B3) supplementation: A crossover randomized clinical trial. (2020, randomised trial)
- The effects of NAD+ precursor (nicotinic acid and nicotinamide) supplementation on weight loss and related hormones: a systematic review and meta-regression analysis of randomized controlled trials. (2023, systematic review)
- The adverse effects of oral niacin/nicotinamide - an overview of reviews. (2025, systematic review)
- Definition of a tolerable upper intake level of niacin: a systematic review and meta-analysis of the dose-dependent effects of nicotinamide and nicotinic acid supplementation. (2017, meta-analysis)
- Mechanistic Basis and Clinical Evidence for the Applications of Nicotinamide (Niacinamide) to Control Skin Aging and Pigmentation. (2021, review)
- Possible Adverse Effects of High-Dose Nicotinamide: Mechanisms and Safety Assessment. (2020, review)
- The Promise of Niacin in Neurology. (2023, review)
- Nicotinamide adenine dinucleotide: Biosynthesis, consumption and therapeutic role in cardiac diseases. (2021, review)
- The chemistry of the vitamin B3 metabolome. (2019, review)
- Nicotinamide Adenine Dinucleotide in Aging Biology: Potential Applications and Many Unknowns. (2023, review)
How much does niacin (vitamin B3) cost?
That depends on the form and the pack, so we work out the price of the same dose of every niacin (vitamin B3) product we can find and rank them.