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Medically reviewed by Vanessa Niles, R.N., M.D., F.A.C.O.G. —
Definition
Nicotinic acid, in plain English
Nicotinic acid is the acid form of vitamin B3. It's found in food and supplements and is turned into NAD+ through a route called the Preiss-Handler pathway.
In doses well above nutritional needs, nicotinic acid widens small blood vessels in the skin, causing the warm, red, itchy 'niacin flush.' NIH bases its 35 mg adult upper limit for supplemental niacin on this effect.
- Common name
- Niacin
- Known side effect
- Skin flushing
- Route to NAD+
- Preiss-Handler pathway
How it connects
How nicotinic acid relates to NAD+
Nicotinic acid is one of several NAD+ precursors. It reaches NAD+ by a different route from nicotinamide, nicotinamide riboside (NR) and NMN, which feed the salvage pathway.
For your treatment
What nicotinic acid means for NAD+ therapy
Prescription nicotinic acid has been used to lower cholesterol since the 1950s, according to StatPearls. High doses can harm the liver, so never take large amounts without a doctor's supervision.
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Questions
Nicotinic acid: common questions
What is nicotinic acid?
Nicotinic acid is the form of vitamin B3 most people mean by 'niacin.' In large doses it causes skin flushing, and it has been used as a prescription cholesterol medicine.
Why does niacin make my skin red?
Nicotinic acid widens small blood vessels in the skin. The flush usually fades on its own but can be uncomfortable; tell a doctor if it's severe.
Is nicotinic acid the same as nicotinamide?
No. Both are vitamin B3, but nicotinamide doesn't usually cause flushing and reaches NAD+ through a different pathway.
Can I take precursors with NAD+ therapy?
Combining them hasn't been studied. Tell your provider about any NR, NMN, niacin or other supplements before you start.
Can I get enough NAD+ from food?
Food supplies niacin and tryptophan, which your body turns into NAD+, and NIH says most people in the U.S. get enough niacin. NAD+ in food is largely broken down during digestion.
Do precursors and NAD+ therapy do the same thing?
Both aim to raise NAD+, by different routes: precursors are converted by the body, while spray and injections deliver NAD+ itself. They haven't been compared in trials.
Keep learning
Related NAD+ terms
Terms that connect to nicotinic acid, each explained on its own page.
- Vitamins & precursorsNiacinNiacin is vitamin B3, an essential nutrient the body turns into NAD and NADP. It includes nicotinic acid and nicotinamide and comes from foods such as poultry, fish, nuts and grains.
- Treatment & safetyNiacin flushNiacin flush is warmth, redness, itching or tingling of the skin, usually on the face and chest, after a large dose of nicotinic acid. It's usually harmless but uncomfortable.
- Vitamins & precursorsNicotinamideNicotinamide, also called niacinamide, is a form of vitamin B3. It's the building block the body recycles to remake NAD+, and unlike nicotinic acid it doesn't cause skin flushing.
- Vitamins & precursorsNAD+ precursorAn NAD+ precursor is any molecule the body can turn into NAD+. The main ones are tryptophan, nicotinic acid, nicotinamide, nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN).
Guides that cover nicotinic acid
Official sources
Nicotinic acid: sources and official resources
Official government and research sources behind this page, so you can check the facts yourself.
- NIH Office of Dietary SupplementsNiacin: Health Professional Fact Sheet
Explains how the body turns niacin (vitamin B3) into NAD, a coenzyme used by more than 400 enzymes.
- NIH National Library of Medicine (StatPearls)Niacin (StatPearls, archived)
Clinical review: NAD and NADP as the active forms of niacin, and niacin's use as a cholesterol drug.
- MedlinePlus (National Library of Medicine)Niacin and niacinamide (Vitamin B3)
Uses, safety and interactions of the two main forms of vitamin B3.
- NIH Office of Dietary SupplementsNiacin: Fact Sheet for Consumers
What niacin (vitamin B3) does, how much adults need and which foods provide it.
Medically reviewed by Dr. Vanessa Niles, R.N., M.D., F.A.C.O.G., on October 12, 2026. This glossary is general education, not medical advice. NAD+ has no FDA-approved use, and compounded NAD+ is not FDA-approved or evaluated by the FDA for safety or effectiveness. Talk with a licensed provider before starting any supplement or treatment.
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