Biological Overview
Niacinamide (also called nicotinamide) is one of two principal forms of vitamin B3, the other being niacin (nicotinic acid). Both are converted by the body into NAD+ and NADP+, coenzymes essential for hundreds of metabolic reactions, but the two forms behave quite differently once ingested. Niacin activates a skin receptor that produces the well-known "niacin flush" and has cholesterol-modifying effects; niacinamide does not activate that receptor and has neither the flush nor the lipid effect. Strictly speaking, vitamin B3 is not a true dietary essential the way some other vitamins are: the body can manufacture niacin internally from the amino acid tryptophan, though inefficiently (roughly 60mg of tryptophan yields about 1mg of niacin), which is why severe deficiency — pellagra, classically remembered by its "3 D's" of dermatitis, diarrhea, and dementia — historically appeared in populations eating corn-based diets poor in both niacin and tryptophan. Niacinamide's most rigorously studied modern use is oral chemoprevention of nonmelanoma skin cancer in high-risk, immunocompetent adults, established in a landmark 2015 randomized trial — a result that, notably, did not replicate when tested in immunosuppressed organ-transplant recipients in a 2023 follow-up trial.
Overview & Classification
- Chemical Class
- Amide derivative of vitamin B3
- Related Compounds
- Niacin, NMN, NR (distinct, see Form Guide)
- Common Forms
- Capsule, tablet; also a topical skincare ingredient
- Official Adult UL
- 35 mg/day (niacin-equivalents basis)
- Key Trial Dose
- 500 mg twice daily for 12 months
- Causes Flushing
- No
- FDA Status
- Dietary supplement; not an approved drug
- Pregnancy Status
- Limited high-dose data; consult provider
Natural Food Sources
Unlike most of this page, which focuses on therapeutic supplement doses, this section covers ordinary dietary niacin — how much people get from food, and why deficiency is now rare in industrialized countries.
| Food Category | Niacin Content | Notes |
|---|---|---|
| Animal proteins (poultry, beef, pork, fish) | ~5–10 mg per serving | Mostly in the highly bioavailable NAD/NADP forms [8] |
| Plant foods (nuts, legumes, whole grains) | ~2–5 mg per serving | Mainly as nicotinic acid; somewhat less bioavailable than animal sources |
| Fortified foods (bread, breakfast cereal, infant formula) | Varies, often substantial | Added niacin is in its free form, making it highly bioavailable |
| Tryptophan-rich foods (turkey, dairy, eggs) | Indirect source | The body converts dietary tryptophan to niacin at roughly 60mg tryptophan : 1mg niacin |
| Unprocessed corn | High total content, poorly absorbed | Niacin is bound to carbohydrate and largely unavailable unless the corn is nixtamalized (treated with lime, the traditional step in tortilla-making) — a historical reason corn-dependent diets without this processing step were linked to pellagra outbreaks [17] |
Nutritional Requirements by Life Stage
Official intake recommendations, measured in niacin equivalents (NE), where 1 NE equals 1mg of niacin or 60mg of dietary tryptophan.
| Life Stage | RDA / AI | Tolerable Upper Intake Level (UL) |
|---|---|---|
| Infants, 0–6 months | 2 mg/day (AI) | Not established |
| Infants, 7–12 months | 4 mg NE/day (AI) | Not established |
| Children, 1–3 years | 6 mg NE/day | 10 mg/day |
| Children, 4–8 years | 8 mg NE/day | 15 mg/day |
| Children, 9–13 years | 12 mg NE/day | 20 mg/day |
| Adolescents, 14–18 years (male) | 16 mg NE/day | 30 mg/day |
| Adolescents, 14–18 years (female) | 14 mg NE/day | 30 mg/day |
| Adults, 19+ years (male) | 16 mg NE/day | 35 mg/day |
| Adults, 19+ years (female) | 14 mg NE/day | 35 mg/day |
| Pregnancy | 18 mg NE/day | 35 mg/day |
| Lactation | 17 mg NE/day | 35 mg/day |
Source: NIH Office of Dietary Supplements / Institute of Medicine Dietary Reference Intakes. [8][9]
How does this compare to the skin-cancer trial dose?
The adult UL of 35mg/day is roughly 29 times smaller than the 1,000mg/day dose used in the ONTRAC skin-cancer chemoprevention trial. As covered in Dosage & Safety, this gap exists because the UL is built around niacin's flushing threshold, not niacinamide-specific toxicity data — it is not a statement that 1,000mg/day is unsafe.
Why does pregnancy have a higher RDA?
The increase reflects the higher energy expenditure of pregnancy and the metabolic demands of supporting fetal development, calculated by the Institute of Medicine from the non-pregnant adult requirement plus an additional margin specific to gestation.
Niacinamide Benefits
Niacinamide's evidence is unusually concentrated in one well-studied area — and unusually honest about where that evidence stopped working.
- The ONTRAC trial, a phase 3 randomized, double-blind, placebo-controlled study in 386 high-risk adults, found 500mg of nicotinamide twice daily for 12 months reduced new nonmelanoma skin cancers by 23% versus placebo. [1]
- Reductions were seen for both major skin cancer types, though only the squamous-cell carcinoma reduction (30%) reached conventional statistical significance on its own; the basal-cell carcinoma reduction (20%) did not.
- Honest caveat: the protective effect did not persist once nicotinamide was stopped — there was no evidence of benefit in the 6-month period after the trial's 12-month intervention ended.
- A pre-specified ONTRAC substudy assessing neurocognitive function and quality of life found no significant effect of nicotinamide on either measure — reassuring in that it found no harm, but no added cognitive benefit either. [10]
- The follow-up ONTRANS trial tested the identical protocol in 158 immunosuppressed solid-organ transplant recipients, a population with a much higher skin cancer burden than the general public. [2]
- It found no significant difference in new skin cancers or actinic keratoses between the nicotinamide and placebo groups.
- Genuinely contested: the trial closed early due to low recruitment, and researchers remain divided on whether this reflects a true absence of benefit in immunosuppressed patients or simply an underpowered trial. [3]
- In the same ONTRAC trial, actinic keratosis (precancerous skin lesion) counts were significantly lower in the nicotinamide group at every measured time point: 11% lower at 3 months, 14% at 6 months, 20% at 9 months, and 13% at 12 months. [1]
- This was one of the most statistically robust findings in the trial, with p-values well below 0.01 at most time points.
- Niacinamide is readily converted into NAD+, NADH, NADP+, and NADPH, coenzymes central to cellular energy production and DNA maintenance.
- The part rarely mentioned: niacinamide can also directly inhibit sirtuins, the NAD+-dependent enzymes most associated with cellular repair and longevity research — a real, laboratory-documented paradox covered in Mechanisms below. [6]
- Topical niacinamide (the form used in most skincare serums) has separate research supporting improved skin barrier function, reduced redness, and acne benefits when applied directly to skin.
- Important distinction: this is a different route of administration with a different evidence base from the oral chemoprevention research that is the focus of this page; the two should not be conflated when evaluating "does niacinamide work" claims.
- Niacinamide has been studied historically for a possible protective effect on insulin-producing pancreatic beta cells, motivated by laboratory findings that it can reduce certain forms of beta-cell damage.
- This line of research has not produced a clinical use recommendation, and people with diabetes should be aware that niacinamide can affect blood sugar regulation — see Safety below.
- Nicotinamide is being actively studied for protecting retinal ganglion cells from glaucoma-related damage, with proposed mechanisms involving restoring depleted NAD+ levels and improving blood flow to the optic nerve. [15]
- A 2025 joint guidance document from the American Glaucoma Society and American Academy of Ophthalmology explicitly states nicotinamide is not yet approved for glaucoma and its safety at the doses studied (up to 3g/day in some trials) remains under evaluation, with documented cases of drug-induced liver injury at that dose in trial participants.
- Important distinction the French source got backwards: niacin (not nicotinamide) is the form experts explicitly advise against using for glaucoma, since it has shown no benefit and carries a higher hepatotoxicity risk; nicotinamide is the one under active investigation.
Clinical Indications by Evidence Tier
Niacinamide has one major, well-documented clinical indication: skin cancer chemoprevention. The trial behind it is genuinely strong — and the full picture, including where it stopped working, is below.
- What it's used for: reducing the rate of new nonmelanoma skin cancers (basal-cell and squamous-cell carcinoma) and precancerous actinic keratoses in adults with a history of skin cancer — an oral, daily preventive use, not a treatment for existing cancer.
- ONTRAC (2015, NEJM, n=386, immunocompetent adults): 500mg nicotinamide twice daily for 12 months reduced new nonmelanoma skin cancers by 23% (P=0.02) versus placebo, with one independent commentary later calculating the true effect size may have been statistically overrepresented. [1][4]
- ONTRANS (2023, NEJM, n=158, solid-organ transplant recipients): the identical 500mg-twice-daily, 12-month protocol produced no significant reduction in keratinocyte cancers or actinic keratoses, despite this population's far higher skin cancer burden. [2]
- The accompanying editorial called the interpretation "straightforward: nicotinamide lacks clinical usefulness" in transplant recipients — a conclusion immediately disputed in published correspondence, which argued the trial's premature closure (158 of a planned 254 participants) made a missed true effect entirely plausible. [3]
- Real-world context: despite this unresolved debate, a 2025 retrospective study of nearly 34,000 veterans with prior skin cancer found nicotinamide use associated with a 14% overall skin cancer risk reduction in the general cohort, while transplant recipients specifically again showed no overall benefit — a pattern consistent with the trial data rather than contradicting it. [11]
- Where this leaves clinical practice: roughly three-quarters of surveyed Mohs surgeons reported recommending nicotinamide to patients even before ONTRANS, and it remains included in national cancer-treatment guidelines for both major nonmelanoma skin cancer types — meaning clinical adoption has outpaced full resolution of the transplant-population question. [12]
Mechanisms of Action
Niacinamide's UV-protective effects and its identity as a NAD+ precursor come from distinct, sometimes opposing, biochemical actions.
Enhanced UV-Induced DNA Repair
UV radiation depletes cellular ATP and NAD+, energy currency the cell needs to power its own DNA repair enzymes. By replenishing this energy pool, niacinamide enhances the skin's capacity to repair UV-induced DNA damage before it accumulates into the mutations that drive nonmelanoma skin cancer — the central mechanism behind the ONTRAC trial's results. [1]
Reduced UV-Induced Cutaneous Immunosuppression
UV exposure suppresses local skin immune function, partly by impairing Langerhans cells, immune sentinels that normally help detect and clear abnormal cells before they progress to cancer. Niacinamide has been shown to reduce this UV-induced immunosuppressive effect, theoretically helping the skin's own surveillance systems catch problems earlier.
NAD+/NADP+ Precursor for Cellular Energy and Redox Reactions
Niacinamide is converted inside cells into NAD+, NADH, NADP+, and NADPH, coenzymes required for hundreds of metabolic and redox reactions, including the energy-generating pathways that power most cellular processes. This is the broad mechanistic basis for niacinamide's general "cellular energy" marketing claims, distinct from its specific UV-protection mechanisms above.
Paradoxical Sirtuin (SIRT1) Inhibition
In a genuinely counterintuitive finding, physiological concentrations of nicotinamide directly inhibit SIRT1 and related sirtuin enzymes — the same NAD+-dependent proteins central to cellular repair and longevity research — by chemically interfering with the reaction these enzymes use to consume NAD+. [6] Follow-up research suggests this inhibition may be transient in living cells, since nicotinamide is rapidly converted into NAD+ itself, temporarily depleting the inhibitor while raising the substrate. [7] The net real-world effect of this push-and-pull remains an active research question, not a settled one.
Why It Doesn't Cause the Niacin Flush
Niacin (nicotinic acid) activates a cell-surface receptor (GPR109A) on skin cells, triggering the release of vasodilating prostaglandins responsible for the characteristic flush, warmth, and redness. Niacinamide does not meaningfully activate this receptor, which is the direct structural reason it produces neither the flush nor niacin's associated cholesterol-modifying effects, despite both compounds converting into the same downstream coenzymes.
Dosage & Timing
Niacinamide has one specific, well-documented research dose, and a large, rarely-explained gap between official guidance and that research dose.
| Goal | Typical Dose | Timing / Notes | Evidence Base |
|---|---|---|---|
| Skin cancer chemoprevention (high-risk, immunocompetent) | 500 mg twice daily (1,000 mg/day) | Sustained for 12 months in the trial; with food to reduce GI upset | ONTRAC trial [1] |
| Transplant recipients (tested, not shown effective) | 500 mg twice daily (1,000 mg/day) | Same protocol as ONTRAC; did not show benefit in this population | ONTRANS trial [2] |
| General NAD+/cellular energy use | No dedicated dose-finding trials | Doses in general-wellness products vary widely without a defined optimal dose | Mechanistic rationale only |
| Official Tolerable Upper Intake Level | 35 mg/day | Based primarily on niacin's flush effect, not niacinamide-specific data | Institute of Medicine DRI [9] |
| Liver toxicity threshold observed in case reports | ~3,000 mg/day | Compares to a lower ~1,500mg/day threshold for nicotinic acid (niacin) | NIH ODS Niacin Fact Sheet [8] |
Why is the official limit so much lower than the trial dose?
The 35mg/day Tolerable Upper Intake Level set by the Institute of Medicine applies to all forms of niacin, including niacinamide, but its scientific basis is built primarily around niacin's flushing threshold, not niacinamide-specific toxicity data. This creates a genuine, rarely-explained gap between conservative official guidance and the doses (1,000mg/day) actually used and tolerated in the largest niacinamide clinical trial to date.
Does it need to be taken indefinitely?
Based on the ONTRAC trial, the skin-cancer protective effect appears to require ongoing use — there was no evidence of continued benefit in the 6 months after the 12-month treatment period ended. This is a meaningful practical consideration distinct from supplements where benefits might be expected to persist after stopping.
Niacin vs. Niacinamide vs. NMN vs. NR
Four different vitamin B3-related compounds get marketed under overlapping language. They are not interchangeable, and confusing them is one of the most common mistakes in this supplement category.
"Vitamin B3" is a category, not one compound — and the differences matter clinically
Niacin, niacinamide, NMN, and NR all eventually contribute to the body's NAD+ pool, but they have meaningfully different side-effect profiles, costs, and human evidence bases. The skin-cancer research on this page specifically used niacinamide — not niacin, not NMN, not NR.
| Form | Causes Flush? | Key Property | Human Evidence |
|---|---|---|---|
| Niacin (nicotinic acid) | Yes | Lowers LDL, raises HDL; used clinically for cholesterol | Decades of cardiovascular research; distinct from skin-cancer findings |
| Niacinamide (nicotinamide) | No | The compound used in the ONTRAC skin-cancer trial; inhibits sirtuins in vitro | Large RCT in skin cancer; decades of general safety data |
| NMN (nicotinamide mononucleotide) | No | More direct NAD+ precursor; primarily marketed for longevity | Smaller, newer human trials; long-term data still limited |
| NR (nicotinamide riboside) | No | Activates rather than inhibits SIRT1 in cellular research, unlike niacinamide [7] | Growing but still smaller human evidence base than niacinamide |
If a product just says "Vitamin B3," which is it?
Check the supplement facts panel for the specific compound name. "Niacin" or "nicotinic acid" is the flushing, cholesterol-active form. "Niacinamide" or "nicotinamide" is the non-flushing form with the skin-cancer research behind it. NMN and NR will be labeled by their full names since they are marketed as distinct, premium ingredients.
Which one should I actually buy?
For most people, niacinamide is the stronger practical choice. It's the only one of the four with a large, completed human clinical trial behind it, it costs a fraction of NMN or NR per dose, and it has decades of accumulated safety data. NMN and NR are reasonable if cost isn't a concern and someone specifically wants to avoid niacinamide's lab-documented sirtuin-inhibition effect, but neither has anything close to niacinamide's level of human evidence yet — the newer compounds are still catching up, not pulling ahead.
Drug Interactions
These are documented clinical interactions, not theoretical mechanisms alone.
| Interaction | Evidence Level | What the Evidence Shows |
|---|---|---|
| Isoniazid & pyrazinamide | Documented, Opposite Direction | Unlike the interactions above, this one runs the other way: these tuberculosis drugs are structurally similar to niacin and competitively inhibit its intestinal absorption and endogenous synthesis, which can deplete the body's niacin/niacinamide stores enough to cause drug-induced pellagra. This is a recognized, published complication of isoniazid therapy, particularly in slow acetylators and people with poor baseline nutrition. [14] |
| Carbamazepine | Documented, Moderate | Niacinamide may slow the breakdown of carbamazepine, raising blood levels; documented in pediatric epilepsy case reports, though the clinical significance is debated when multiple anticonvulsants are involved. [13] |
| Primidone | Documented, Moderate | Similar mechanism to carbamazepine: niacinamide may slow primidone breakdown, raising blood levels, documented in pediatric case reports. |
| Warfarin and other blood thinners | Theoretical, Mechanism-Based | Niacinamide may slow blood clotting; combining it with anticoagulant or antiplatelet medication could theoretically increase bruising or bleeding risk. |
| Hepatotoxic medications | Theoretical, Dose-Dependent | At high doses, niacinamide itself carries a liver-stress risk; combining it with other medications known to affect the liver compounds that risk. |
| Diabetes medications | Mechanism-Based | Niacinamide may raise blood sugar in some individuals, which could work against the intended effect of glucose-lowering medications; regular monitoring is advised. |
Safety & Toxicity Thresholds
When to Use Caution
- Diabetes: niacinamide might raise blood sugar; people with diabetes taking it regularly should monitor glucose more closely.
- Gout: niacin clearly raises uric acid levels and is a recognized gout risk at high doses; the evidence for niacinamide doing the same is smaller and mixed, but caution is still reasonable for anyone predisposed to gout. [16]
- Liver and gallbladder conditions: niacinamide can stress the liver at high doses and may worsen existing gallbladder disease.
- Peptic ulcers: niacinamide may aggravate stomach or intestinal ulcers and is generally not recommended in this condition.
- Kidney dialysis: niacinamide use has been associated with an increased risk of low platelet counts in patients with kidney failure on dialysis.
- Before surgery: niacinamide may interfere with blood sugar control during and after surgery; stopping at least two weeks beforehand is commonly advised.
Genuinely Unusual Details
- A real cardiovascular scare, then real reassurance: nicotinamide metabolites were implicated in cardiovascular risk via a VCAM-1-related mechanism, but a 2025 retrospective cohort study of over 13,000 patients found no increased risk of major adverse cardiovascular events tied to actual nicotinamide use — the strongest predictor of future events was simply a prior history of such events. [5]
- The official safety limit doesn't reflect the research dose: the 35mg/day Tolerable Upper Intake Level is built on niacin's flush threshold, not niacinamide's actual toxicity profile — the largest niacinamide trial to date used 1,000mg/day, nearly 30 times that figure, without significant adverse events. [9]
- It can inhibit the enzymes it helps fuel: as covered in Mechanisms, niacinamide directly inhibits sirtuins in laboratory research, the same NAD+-dependent enzymes central to cellular repair and longevity science — a genuine double-edged property of the same molecule, not a contradiction between separate studies. [6]
- The ONTRAC vs. ONTRANS gap remains genuinely unresolved rather than a simple matter of "it doesn't work in transplant patients" — the underpowered, early-terminated trial design means the scientific community itself has not reached consensus on this question.
FAQ
Does niacinamide actually reduce skin cancer risk?
Why didn't niacinamide work the same way in organ transplant patients?
What's the actual difference between niacin and niacinamide?
Is niacinamide the same as NMN or NR supplements for longevity?
Does niacinamide increase heart attack or cardiovascular risk?
How much niacinamide is safe, and for how long?
Bibliography
The New England Journal of Medicine, JAMA Dermatology, Journal of Biological Chemistry, and NIH/IOM regulatory documents for all clinical claims. No secondary aggregator was cited as a source for any specific figure.
Related
- Astaxanthin — another UV-related supplement with real but modest RCT-backed skin effects, explicitly not a sunscreen substitute
- Vitamin C — another vitamin with a wide gap between its official RDA/UL and the doses used in its strongest clinical trials