Vitamin B3 Side Effects: Is It Harmful? What Science Says

No, vitamin B3 (niacin) does not harm most people when consumed at recommended doses. Problems arise with doses far above daily requirements, especially in the form of nicotinic acid, which causes skin flushing and, at pharmacological doses, is associated with liver and metabolic risks. The central question is not "does it do harm or not", but "at what dose, in what form and for whom".

This article explains what vitamin B3 is, why it is essential, what the real side effects are, who should be careful and what the scientific evidence actually shows — without exaggeration or alarmism.

What is vitamin B3 and why does your body need it?

Vitamin B3 is a term that groups two main forms: nicotinic acid (niacin) and nicotinamide (niacinamide). Both are precursors of essential coenzymes — NAD and NADP — which are involved in hundreds of metabolic reactions, including the production of energy from food ¹.

The body does not produce enough B3 on its own, so it depends on the diet. Common sources include meat, fish, poultry, whole grains, legumes and nuts. Severe deficiency causes pellagra, a disease characterised by dermatitis, diarrhoea and dementia — currently rare in Western countries, but still present in populations with severe malnutrition ².

In Portugal, most people get enough B3 through diet. Supplementation makes more sense in specific situations, such as a restricted diet or increased needs, and should be guided by a health professional.

Does vitamin B3 do harm? The most common side effects

The best-known effect of nicotinic acid is skin flushing: redness, heat and itching, especially on the face and chest, which appears shortly after taking it. This happens because niacin dilates blood vessels. It is uncomfortable, but not dangerous, and tends to decrease with continued use or with a lower dose.

Nicotinamide does not cause flushing, which generally makes it better tolerated. However, both forms can cause, in some people, gastrointestinal discomfort, nausea or headaches, especially at higher doses ².

These effects are more likely at doses above the recommended ones and tend to ease when you lower the dose or take the supplement with food.

High doses: when B3 becomes a risk

The tolerable upper intake level set in Europe is 10 mg per day for nicotinic acid and 900 mg per day for nicotinamide. These values are not targets to reach — they are limits above which the risk of adverse effects increases. Note that the 10 mg per day limit applies specifically to nicotinic acid as a pharmacological form; the recommended total niacin intake (14 to 16 mg per day) refers to all forms together and does not contradict that value.

Pharmacological doses of niacin (500 to 2000 mg per day) were used in the past to improve lipid profiles, but that use has fallen out of favour due to side effects and the availability of more effective and safer alternatives. Those doses should only be considered under strict medical supervision.

These risks are not theoretical: there are documented reports of people who developed hepatitis or liver failure after taking high doses of sustained-release niacin. That is why niacin should not be taken without medical supervision at high doses.

The risks associated with very high and prolonged doses include:

• Liver injury (hepatotoxicity), especially with sustained-release formulations
• Increased uric acid, relevant for people with gout
• Changes in blood glucose control, relevant for people with diabetes
• Interactions with medicines, including anticoagulants and antihypertensives

Other effects described with very high doses include gastric ulcers and blurred vision.

A metabolomics study published in 2024 raised an additional question: high levels of terminal niacin metabolites (2PY and 4PY) were associated with a higher risk of major cardiovascular events in patients with stable cardiovascular disease, in three cohorts (n=1162, n=2331 and n=832) ³. This is an observational finding in people with established cardiovascular disease — it does not mean that niacin causes problems in healthy people who consume it at normal doses, but it reinforces the importance of not exceeding recommended doses without medical advice.

Who should take special care with vitamin B3?

Some groups should avoid high doses or talk to a health professional before supplementing:

• People with liver disease
• People with peptic ulcer or a history of gastric problems
• People with gout (niacin can raise uric acid)
• People with diabetes or insulin resistance (it can affect glucose control)
• Pregnant or breastfeeding women — requirements are usually met by diet; supplements only on medical advice
• People taking blood pressure medicines, anticoagulants or anticonvulsants

If you belong to any of these groups, do not start supplementing without first talking to a doctor or pharmacist. Even outside these groups, doses above 35 mg per day warrant a conversation with a professional.

If you are thinking about taking doses above 35 mg per day, that conversation with a health professional is especially important.

Is vitamin B3 safe? What the evidence says

At recommended doses — around 14 to 16 mg per day for adults — vitamin B3 is considered safe and most people get that amount through diet.

Nicotinamide is generally well tolerated. In studies with oral supplements of NAD precursors, such as nicotinamide mononucleotide (NMN) and nicotinamide riboside (NR), no significant adverse events were observed in healthy adults over periods of 4 to 12 weeks, with doses ranging from 100 mg to 1000 mg per day ^{4 5 6}. These studies assessed safety and tolerability, not clinical benefits, and the doses used are much higher than nutritional requirements. Note that one of these studies was carried out in older adults with mild cognitive impairment, so the results are not directly generalisable to the whole healthy adult population ⁶.

A 2024 systematic review, which analysed 10 studies with 489 participants across various clinical conditions, concluded that supplementation with NAD and its precursors was well tolerated ⁷. However, this review included specific populations (such as patients with chronic fatigue syndrome, Parkinson's or Alzheimer's), so the results are not directly generalisable to healthy adults.

A more recent systematic review, which analysed 33 human intervention studies, confirmed that oral NR and NMN were generally well tolerated over weeks to months, but the effects on functional and metabolic outcomes were heterogeneous and often null ⁸. In other words: safety is reasonably consistent, but benefits beyond correcting deficiency are not established.

Vitamin B3 in gummies: what the label says

TuttiBear Skin Hydration and Firmness Gummies include niacin (vitamin B3) in the formulation: each serving of 2 gummies provides 16 mg of niacin, which corresponds to 100% of the reference value for adults. The product is intended for adults, with directions to chew 2 gummies per day, preferably after a meal.

It is important to note that 16 mg per day is within recommended doses and well below the upper safety limits. However, if you already take other sources of B3 (multivitamins, for example), it is worth adding up the amounts to avoid exceeding the reference value unnecessarily.

The label warnings include: do not exceed the recommended daily dose; supplements do not replace a varied and balanced diet; keep out of reach of children; in case of pregnancy, breastfeeding, illness or taking medicines, consult a health professional before use; contains polyols (excessive consumption may have a laxative effect).

If you already take other sources of B3, such as multivitamins, add up the amounts to avoid exceeding the reference value unnecessarily. The tolerable upper intake level set by EFSA for nicotinic acid is 10 mg per day and for nicotinamide it is 900 mg per day ⁹; the EU reference value for niacin is 16 mg per day ¹⁰.

To learn more about the adequate daily dose, see the article on vitamin B3 daily dose.

Vitamin B3 oral or topical: they are different things

Topical niacinamide (applied to the skin) has evidence of benefits for the skin barrier and for reducing redness, at concentrations of 2% to 5%. A 2020 Cochrane review, which included 49 trials with 3880 participants with mild to moderate acne, assessed topical treatments such as nicotinamide, but the evidence on its effectiveness as a standalone treatment remained uncertain ¹¹.

Taking B3 orally is different from applying it to the skin. The evidence that oral B3 supplementation improves the skin in healthy people is limited. If your goal is skin health, the topical route has more scientific support for that specific purpose.

For a broader view of what B3 does in the body, see the article how does vitamin B3 work.

Myths and truths about vitamin B3

Myth: vitamin B3 is toxic and should be avoided

B3 is an essential vitamin. Without it, energy metabolism and cell repair are compromised. The problem is not the vitamin itself, but excessive doses. At recommended doses, it is safe.

Myth: B3 gives instant energy

B3 takes part in energy metabolism, but it is not a stimulant. It does not produce an immediate effect like caffeine. Energy comes from metabolism functioning properly, not from a sudden boost.

Myth: the more B3, the better for the skin

For the skin, topical niacinamide has evidence of benefits. But taking high-dose oral supplements does not necessarily improve the skin and can cause side effects. Excess B3 is excreted in urine, not stored.

Truth: B3 can interact with medicines

Niacin can enhance the effect of blood pressure medicines, causing dangerous drops in blood pressure, and can increase the effect of anticoagulants, raising the risk of bleeding. If you take medication, talk to your doctor before supplementing.

The limit of the evidence: what we still do not know

There are no studies that determine exactly at what dose B3 starts to be problematic for each person. Tolerance varies: some people flush at 50 mg, others tolerate 500 mg without significant discomfort. What we know is that the risk increases with dose and with duration of use.

It is also not established whether oral B3 supplementation brings skin benefits in healthy people. The evidence is insufficient to claim benefits in that context. If the goal is skin health, the topical route has more support. If the goal is general health, a balanced diet is usually enough.

If you have doubts about whether to take B3, talk to a pharmacist or doctor. They can assess your specific situation, including medication and health conditions. Do not rely on opinions from forums or influencers for decisions about supplementation.

How to choose a vitamin B3 supplement

If you decide to supplement, prefer products with doses within the reference value (around 16 mg per day) and avoid sustained-release nicotinic acid formulas without medical advice. Check the label to confirm the form of B3 used (nicotinamide or nicotinic acid) and the amount per serving.

To compare formats, see the article vitamin B3 gummies vs tablets. If you are unsure about the best time to take it, see when to take vitamin B3.

In case of pregnancy, breastfeeding, illness or taking medicines, always consult a health professional before starting any supplement.

Frequently asked questions

Does vitamin B3 harm the liver?

At recommended doses (around 16 mg per day), there is no evidence of liver risk. The risk arises with very high pharmacological doses (500 to 2000 mg per day), especially with sustained-release nicotinic acid formulations. Those doses should only be used under medical supervision.

What is the safe dose of vitamin B3 per day?

For adults, the recommended dose is around 14 to 16 mg per day. The tolerable upper intake level in Europe is 10 mg per day for nicotinic acid and 900 mg per day for nicotinamide. These limits are not targets to reach, but values above which the risk of adverse effects increases. The 10 mg per day limit applies specifically to nicotinic acid as a pharmacological form.

Does vitamin B3 cause skin flushing?

Yes, nicotinic acid (niacin) can cause skin flushing — redness, heat and itching, especially on the face and chest. Nicotinamide does not cause this effect. Flushing is uncomfortable but not dangerous and tends to decrease with continued use or with a lower dose.

Can I take vitamin B3 every day?

Yes, within recommended doses. Most people get enough B3 through diet and do not need supplements. If you choose to supplement, pick a dose within the reference value and do not exceed the dose stated on the label without medical advice.

Does oral vitamin B3 improve the skin?

The evidence that oral B3 supplementation improves the skin in healthy people is limited. Topical niacinamide (applied to the skin) has more scientific support for benefits to the skin barrier and for reducing redness. These are different routes and should not be confused.

Who should not take vitamin B3?

People with liver disease, peptic ulcer, gout, diabetes or insulin resistance should take special care. Pregnant and breastfeeding women should only supplement on medical advice. Anyone taking blood pressure medicines, anticoagulants or anticonvulsants should talk to a health professional before supplementing.