Does Nicotinamide Prevent Skin Cancer? Only If You've Had One

The honest answer to whether nicotinamide prevents skin cancer depends entirely on who is asking. For a healthy thirty year old, there is no good evidence it does much of anything. For someone who has already had two skin cancers cut out of their forehead, there is a phase 3 trial in the New England Journal of Medicine that says it lowers the odds of the next one.

That gap is the whole story, and almost nobody tells it in one place. The vitamin costs a few cents a day and sits on the shelf next to far flashier longevity compounds. Its evidence is narrower than theirs, and in its narrow lane it is better than most of them.

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What Is Nicotinamide?

Nicotinamide is one of the two forms of vitamin B3. On a supplement label it usually reads niacinamide, which is the same molecule. It is not niacin. Niacin, the other B3, is nicotinic acid, and it causes the hot, prickly flush people associate with the vitamin. Nicotinamide does not flush, and it is the only form tested in the skin cancer trials, so the distinction is not pedantic. Buy the wrong one and you are taking a different drug.

Inside cells, nicotinamide feeds NAD+, the coenzyme that powers energy production and DNA repair. This is the same B3 to NAD+ pathway that the pricier NAD+ precursor nicotinamide riboside is sold on, though the two are marketed for completely different reasons. Ultraviolet light does two things to skin: it damages DNA, and it briefly suppresses the local immune response that would otherwise catch and clear the damaged cells. UV is also how skin makes the vitamin D behind the sunshine stack, but the DNA damage is the price that comes with it. Nicotinamide appears to blunt both harms. It gives cells the energy currency to repair UV damage faster, and it cushions the immune dip that lets precancerous cells slip through. That is the mechanism the trials were built to test.

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The Science: Does Nicotinamide Prevent Skin Cancer?

The evidence has a clean arc: one strong positive trial in exactly the right population, one flat trial in a harder one, and a large real world dataset that shows where the benefit concentrates. Keeping those three apart is the point.

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The phase 3 trial that started it

• The Evidence: The ONTRAC trial randomized 386 adults who had each had at least two nonmelanoma skin cancers in the previous five years to 500 mg of nicotinamide twice a day or placebo for 12 months. New nonmelanoma skin cancers fell by 23 percent in the nicotinamide group (95% CI 4 to 38, P=0.02). Squamous cell carcinomas dropped about 30 percent, and actinic keratoses, the rough precancerous spots, were roughly 13 percent lower at the one year mark.
• Read the study: A Phase 3 Randomized Trial of Nicotinamide for Skin-Cancer Chemoprevention

Two details keep this honest. The 23 percent is a relative reduction inside an already high risk group, not a promise for the general public. And the protection did not persist once people stopped: off treatment, the benefit faded. Nicotinamide does not fix the underlying damage. It keeps a lid on it while you take it.

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Where the same design found nothing

The obvious next question is whether it helps the people at the very highest risk. Organ transplant recipients take drugs that suppress the immune system, and their skin cancer rates run many times the background rate.

• The Evidence: The ONTRANS trial ran the same 500 mg twice daily protocol in transplant recipients who had had at least two keratinocyte cancers. It found no benefit, with the rate of new cancers essentially the same as placebo. The trial was stopped early after enrolling 158 of a planned 254, so it was underpowered, but the result pointed at nothing.
• Read the study: Nicotinamide for Skin-Cancer Chemoprevention in Transplant Recipients

An underpowered null is not proof of no effect, and the early stop matters. But it is a genuine caution against assuming the ONTRAC result carries over to everyone at high risk. In the population where you might most want it to work, it did not.

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The real world signal, and its catch

• The Evidence: A 2025 analysis of Veterans Affairs records covered 33,822 patients and compared 12,287 who took 500 mg of nicotinamide twice daily against matched controls. New keratinocyte cancers were about 14 percent lower overall. The effect concentrated sharply by timing: starting nicotinamide after a first skin cancer was tied to a 54 percent reduction, while starting it only after several prior cancers showed much less.
• Read the study: Nicotinamide for Skin Cancer Chemoprevention

This is a retrospective cohort, not a randomized trial, so the healthy user effect and confounding are live concerns and the exact percentages should be read loosely. What it adds is a plausible pattern. The vitamin looks most useful early, right after a first cancer announces that someone is prone to them, and less useful once the skin is already covered in damage. That fits the biology of a compound that repairs and protects rather than reverses.

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A Practical Guide: How to Use It

If you have a history of nonmelanoma skin cancer or a crop of actinic keratoses, this is one of the few cheap interventions with a phase 3 trial behind it, and it is worth raising with a dermatologist.

The dose is specific. The trial used 500 mg of nicotinamide twice a day, 1,000 mg total, split morning and evening. That is well above the fraction of a gram in a typical B-complex. Buy plain niacinamide, confirm the label says niacinamide or nicotinamide rather than niacin or nicotinic acid, and take it with or without food. It is water soluble and forgiving on timing.

Set the expectation correctly. The benefit is ongoing, not curative. It works while you take it and fades when you stop, so this is a daily habit for as long as your risk stays high, not a course you finish. And it sits on top of the basics rather than replacing them. Sun protection and regular skin checks are still doing most of the work.

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Safety and Advice

Nicotinamide has a long, reassuring safety record at these doses. In the trials, side effects matched placebo. The most important safety point is really about identity: it is not niacin. Take niacin at a gram a day and you get flushing, and at high chronic doses it can stress the liver. Nicotinamide avoids the flush and is far gentler. Even so, more is not better, and there is no reason to go past the studied 500 mg twice daily.

A few people should check first. Anyone with significant kidney or liver disease should talk to a doctor, since both organs handle the vitamin. If you are pregnant or breastfeeding, stay within normal dietary intakes unless a doctor advises otherwise. And here is the limit worth repeating: the strong evidence is for people who have already had nonmelanoma skin cancers. If you have never had one, taking gram doses to prevent a cancer you are at average risk of is not something the trials support.

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The Bottom Line

Does nicotinamide prevent skin cancer? For people with a history of nonmelanoma skin cancer, a phase 3 trial says it modestly does, cutting new cancers by about a quarter while they keep taking it, and the real world data suggests it helps most when started early. For everyone else, it is an unproven habit borrowed from a high risk group. It is cheap, safe, and narrow, and it is not a substitute for sunscreen or skin checks.

If that first group is you, the concrete move is simple: 500 mg of plain niacinamide twice a day, started sooner rather than later, as one line in a plan your dermatologist is already running.

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This article is for educational purposes only and is not medical advice. Supplements can interact with medications and health conditions, so talk to a qualified healthcare provider before starting anything new.