The dose used in the landmark clinical trial, and the one most dermatologists now recommend, is 500 mg of nicotinamide taken twice daily, for a total of 1,000 mg per day. That specific regimen reduced new nonmelanoma skin cancers by roughly a quarter in high-risk patients over 12 months. But the dose alone does not tell the whole story: the form of vitamin B3 matters, the timing of when you start matters, and the benefit does not extend equally to everyone.
Where the 500 mg Twice Daily Dose Comes From
The dosing standard traces back to the ONTRAC trial, a phase 3 randomized controlled trial published in the New England Journal of Medicine. Researchers enrolled 386 people who had each had at least two nonmelanoma skin cancers in the previous five years and randomly assigned them to receive either 500 mg of nicotinamide twice daily or a placebo for 12 months. At the end of the year, the nicotinamide group had a 23% lower rate of new nonmelanoma skin cancers compared to placebo.1PubMed. A Phase 3 Randomized Trial of Nicotinamide for Skin-Cancer Chemoprevention The reduction was somewhat larger for squamous cell carcinomas specifically, at about 30%, while basal cell carcinomas dropped by around 20%.2New England Journal of Medicine. A Phase 3 Randomized Trial of Nicotinamide for Skin-Cancer Chemoprevention Actinic keratoses, the rough scaly patches that serve as precursors to skin cancer, also fell significantly across the trial period.
An earlier study had tested both 500 mg and 1,500 mg daily doses and found that both significantly reduced UV-induced immune suppression in the skin, with no added benefit seen at the higher amount.3PubMed. Oral nicotinamide protects against ultraviolet radiation-induced immunosuppression in humans So the 500 mg twice daily dose was not arbitrary. It was selected because it appeared to be the sweet spot: enough to produce a measurable protective effect, without any clear advantage from going higher.
How Nicotinamide Protects Against Skin Cancer
Nicotinamide works through a mechanism that is different from sunscreen, which blocks UV rays from reaching the skin in the first place. Instead, nicotinamide helps the skin recover after UV damage has already occurred. It does this by boosting the cell’s internal energy supply. Nicotinamide is a building block for a molecule called NAD+, which is central to how cells produce energy. UV radiation depletes that energy, and DNA repair is an energy-hungry process. When nicotinamide keeps energy levels up, skin cells can fix UV-damaged DNA more quickly and more completely.4PubMed. Nicotinamide enhances repair of ultraviolet radiation-induced DNA damage in human keratinocytes and ex vivo skin Laboratory work confirmed this: skin cells treated with nicotinamide and then hit with UV light showed a higher rate of DNA repair activity compared to cells that got only UV exposure.5PLOS ONE. Nicotinamide Enhances Repair of Arsenic and Ultraviolet Radiation-Induced DNA Damage in HaCaT Keratinocytes and Ex Vivo Human Skin
There is also an immune component. UV exposure suppresses the skin’s local immune response, which is one reason sun damage accumulates into cancer over time. Your skin becomes less able to detect and destroy abnormal cells in areas that keep getting burned. Nicotinamide, whether applied topically or taken orally, significantly protected against this UV-induced immune suppression in human volunteers.6PubMed. Topical nicotinamide modulates cellular energy metabolism and provides broad-spectrum protection against ultraviolet radiation-induced immunosuppression in humans So the supplement works on two fronts: helping cells repair DNA damage and helping the immune system stay alert in sun-exposed skin.
Why Starting Earlier Seems to Matter
A 2025 review published in JAMA Dermatology looked across the available clinical evidence and found something striking about timing. Overall, the data showed a 14% reduction in skin cancer risk with nicotinamide. But when people started taking nicotinamide after their very first skin cancer diagnosis, the risk reduction jumped to 54%. That benefit shrank the longer someone waited, declining with each additional skin cancer before starting the supplement.7PubMed Central. Nicotinamide for Skin Cancer Chemoprevention The implication is intuitive: intervening early, when there is less accumulated damage and fewer precancerous changes already established in the skin, gives nicotinamide more room to make a difference.
This does not mean nicotinamide is useless for people who have already had several skin cancers. The original ONTRAC trial enrolled people with at least two prior cancers and still found that 23% reduction. But the emerging picture suggests that if your dermatologist identifies your first nonmelanoma skin cancer and you start nicotinamide promptly, you may get a substantially larger protective effect than if you wait through several more diagnoses before starting.
Nicotinamide Is Not the Same as Niacin
This is probably the most common point of confusion, and it has real consequences if you get it wrong. Vitamin B3 comes in several forms. The two most familiar are nicotinamide (also called niacinamide) and nicotinic acid (commonly known as niacin). While both serve as vitamin B3 and are used by the body to make NAD+, they behave very differently as supplements. Niacin at high doses causes flushing, a sometimes intense skin reddening, warmth, and tingling that can be quite uncomfortable. It can also cause headaches and drops in blood pressure. Nicotinamide does not cause these side effects.8PubMed Central. Niacin intake and risk of skin cancer in US women and men
All of the clinical trial evidence for skin cancer prevention used nicotinamide, not niacin. The two are not interchangeable for this purpose. When you are shopping for a supplement, look specifically for “nicotinamide” or “niacinamide” on the label. Do not buy a niacin supplement expecting the same result. You will get flushing and possibly nothing useful for your skin. Another form, nicotinamide riboside, is marketed as a longevity supplement, but it has not been tested in skin cancer prevention trials at the same level as plain nicotinamide and is typically much more expensive.
The Transplant Recipient Problem
Organ transplant recipients face a dramatically elevated skin cancer risk because the immunosuppressive drugs they take to prevent organ rejection also weaken the skin’s ability to fight off cancerous changes. Given how well nicotinamide worked in the general high-risk population, there was real hope it might help this group too. A dedicated phase 3 trial tested the same dose, 500 mg twice daily, in transplant recipients who had already had at least two keratinocyte cancers. The result was clearly negative. After 12 months, there were 207 new skin cancers in the nicotinamide group and 210 in the placebo group, which was statistically identical.9PubMed. Nicotinamide for Skin-Cancer Chemoprevention in Transplant Recipients No differences were seen for any subtype of cancer or for actinic keratoses.
The JAMA Dermatology review noted a partial exception: when transplant recipients started nicotinamide early, there was some reduction in squamous cell carcinoma specifically. But overall, the evidence does not support recommending nicotinamide as a standard skin cancer prevention strategy for transplant patients.10PubMed Central. Nicotinamide for Skin Cancer Chemoprevention The likely explanation is that nicotinamide works partly through the immune system, and when that system is pharmaceutically suppressed, one of the supplement’s two main protective pathways is essentially disabled. The DNA repair benefit alone was not enough to overcome the massive immune deficit these patients face.
Who Should Consider Taking It
Nicotinamide is not being recommended for everyone as a general-purpose cancer preventive. The evidence supports its use specifically in people at high risk of nonmelanoma skin cancers. In practice, that means people who have already had at least one basal cell carcinoma or squamous cell carcinoma and whose dermatologist expects more. Fair-skinned individuals with extensive histories of sun exposure, people who work outdoors, and those with multiple actinic keratoses are the population where the evidence applies most cleanly.
There is also interest in nicotinamide for people with xeroderma pigmentosum, a rare genetic condition that impairs the body’s ability to repair UV-damaged DNA. Because these patients develop skin cancers at a dramatically accelerated rate, any supplement that enhances DNA repair is attractive. A review of investigational therapies for xeroderma pigmentosum noted the evidence from the ONTRAC trial and the known mechanism by which nicotinamide enhances both major DNA repair pathways, but also acknowledged that no dedicated trials have been conducted in this population, likely because of the difficulty of recruiting enough patients.11PubMed Central. Xeroderma pigmentosum: an updated review
What about melanoma? The evidence there is much thinner. Nicotinamide has been shown to enhance DNA repair in melanocytes, the pigment-producing cells where melanoma originates, which makes it a theoretically promising candidate.12Photodermatology, Photoimmunology & Photomedicine. Melanoma and nonmelanoma skin cancer chemoprevention: A role for nicotinamide? But promising laboratory findings and a plausible mechanism do not equal clinical proof. No large trial has yet demonstrated that nicotinamide reduces melanoma incidence. If melanoma prevention is your primary concern, the evidence does not yet support relying on nicotinamide for that purpose.
Safety and What to Watch For
At 500 mg twice daily, nicotinamide has consistently been well-tolerated in clinical trials. The ONTRAC trial found no significant adverse effects among treated patients, and the earlier dose-finding study also reported good tolerability at both 500 mg and 1,500 mg daily.13PubMed. Oral nicotinamide protects against ultraviolet radiation-induced immunosuppression in humans This is part of what makes nicotinamide attractive as a preventive: it is cheap, widely available, and well-tolerated.
That said, a safety review that looked at what might happen at higher doses or with very long-term use raised some theoretical concerns. At high doses, nicotinamide inhibits enzymes called PARPs that play a role in protecting the genome. It also affects how cells handle methyl groups, which are chemical tags that control gene activity. The review concluded that nicotinamide is safe at current recommended doses but flagged potential risks from chronic use at high doses that could alter gene regulation over time.14PubMed Central. Possible Adverse Effects of High-Dose Nicotinamide: Mechanisms and Safety Assessment Separately, some researchers have noted that because boosting NAD+ increases cellular energy availability, there is a theoretical concern about whether this could fuel the growth of cancers that are already present, since cancer cells are energy-hungry.15PubMed Central. Nicotinamide adenine dinucleotide and the sirtuins caution: Pro-cancer functions
Neither of these concerns has materialized in clinical data at the 500 mg twice daily dose over 12 months. They remain theoretical flags rather than demonstrated harms. But they are worth being aware of, and they are a reasonable argument for sticking to the tested dose rather than taking more on the assumption that higher is better. If you have an active cancer of any kind, talk to your oncologist before starting nicotinamide supplementation.
The Benefit Stops When You Stop
One important practical detail from the ONTRAC trial that often gets overlooked: when participants stopped taking nicotinamide at the end of the 12-month study period, the protective effect disappeared. Their rate of new skin cancers returned to the same level as the placebo group. This means nicotinamide is not creating some lasting change in your skin. It works while you take it and stops working when you quit. If you are in the high-risk category and your dermatologist recommends it, the commitment is ongoing rather than a short course.
This also means nicotinamide is an add-on to sun protection, not a replacement for it. You still need sunscreen, protective clothing, and sensible UV avoidance. Nicotinamide addresses residual damage that gets through your other defenses.16Journal of Dermatology Research. Novel Oral Supplement Protects Against Acute Erythema from Cutaneous UV Exposure and Increases Minimal Erythema Dose Think of it as an extra layer in a multi-layered approach rather than a standalone solution.
Cost and Access
Nicotinamide is available over the counter as a dietary supplement and costs very little compared to most medical interventions. A recent economic analysis modeled the cost-effectiveness of nicotinamide supplementation for keratinocyte carcinoma prevention and found that it was not just cost-effective but actually cost-saving. In their model, nicotinamide supplementation cost roughly $161,000 across a cohort, but the treatment costs avoided for skin cancers that were prevented totaled about $526,000, producing a net savings of roughly $365,000.17JAMA Dermatology. Cost-Effectiveness of Oral Nicotinamide for Keratinocyte Carcinoma Prevention In other words, the supplement pays for itself many times over in avoided surgeries and treatments, at least in the high-risk population where prevention is most impactful.
Because it is sold as a supplement rather than a prescription drug, there is no insurance barrier. You can find nicotinamide in 500 mg capsules at most pharmacies and online retailers for under $20 a month. The flip side of supplement status is that there is no FDA-mandated quality control on the manufacturing, so buying from a reputable brand that undergoes third-party testing (look for USP or NSF certification on the bottle) adds a layer of assurance that you are actually getting what the label says.
Squamous Cell vs. Basal Cell Differences
The ONTRAC trial suggested that nicotinamide’s benefit was somewhat more pronounced for squamous cell carcinomas than for basal cell carcinomas. The rate of new squamous cell carcinomas dropped by about 30% compared to placebo, while the reduction in basal cell carcinomas was around 20% and did not reach statistical significance on its own.18New England Journal of Medicine. A Phase 3 Randomized Trial of Nicotinamide for Skin-Cancer Chemoprevention The broader JAMA Dermatology review confirmed this pattern, noting that the greatest risk reduction across studies was seen for squamous cell carcinomas.19PubMed Central. Nicotinamide for Skin Cancer Chemoprevention
This makes biological sense. Squamous cell carcinomas are more tightly linked to cumulative UV damage and immune suppression than basal cell carcinomas, which have a somewhat more complex relationship with genetics, developmental pathways, and intermittent intense sun exposure. Since nicotinamide’s two main mechanisms, enhanced DNA repair and preserved immune surveillance, both target the consequences of UV exposure, it follows that the cancer type most directly driven by UV damage would respond best. If you have a history dominated by squamous cell carcinomas, the case for nicotinamide supplementation is arguably stronger than if your history is mostly basal cell carcinomas, though both types showed benefit.
What Nicotinamide Cannot Do
Given how inexpensive and well-tolerated nicotinamide is, it is tempting to see it as a miracle supplement for skin cancer. It is not. A 23% reduction in skin cancers in high-risk patients is genuinely meaningful, especially when repeated across someone’s lifetime, but it leaves the majority of cancers still occurring. People in the high-risk category need continued dermatologic surveillance, regular skin checks, and prompt treatment of suspicious lesions regardless of whether they take nicotinamide.
There is also no evidence that nicotinamide helps if you are not in a high-risk group. No trial has tested it in the general population of people with average sun exposure who have never had a skin cancer. The biological reasoning suggests it could be helpful in anyone who gets UV exposure, but “biologically plausible” is a much lower bar than “clinically proven.” The cost is low enough that some dermatologists mention it to patients who ask, even without a formal skin cancer history, but that is an extrapolation beyond the data rather than a guideline-level recommendation.
Dietary niacin intake from food sources like chicken, tuna, mushrooms, and fortified grains contributes to your overall NAD+ pool, but the amounts involved are much lower than what was used in clinical trials. You cannot realistically eat your way to 1,000 mg of nicotinamide per day through food alone. The supplement form is needed to reach the doses that have been tested.