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Medicines and supplements

Can you take niacin with metformin?

Written by the Full Measure editorial team, which sells supplements. Approved for publication by the Full Measure owners. Updated .

Drafted with AI assistance from the sources listed below. How we write these

Quick answer

Ask your pharmacist or doctor before combining. The metformin label lists nicotinic acid, a form of niacin, among drugs that tend to raise blood sugar and may weaken its control. NIH says nicotinic acid at 1.5 g a day or more is most likely to raise blood sugar, and diabetes medicine doses may then need to change.1,2

Key facts

  • The metformin label asks for close watching of blood sugar when a drug such as nicotinic acid is started, and for low blood sugar when it is stopped.1
  • The prescription niacin label says niacin can raise fasting blood sugar and that diabetes treatment may need adjusting.3
  • High doses of nicotinic acid can raise blood sugar even in people who do not have diabetes.4
  • In a large trial described on the niacin label, diabetes was reported as a side effect in 3.6% of people given extended-release niacin, against 2.2% in the comparison group.3

Your doctor may want to check on you

The metformin label lists nicotinic acid among drugs that tend to raise blood sugar and may lead to loss of blood sugar control, and advises close watching when such a drug is started or stopped. NIH says nicotinic acid at 1.5 g a day or more is most likely to raise blood sugar, and that people taking diabetes medicines may need their doses adjusted.1,2,4

On the medicine's label

What is documented

NIH explains that large doses of nicotinic acid can raise blood sugar by causing or worsening insulin resistance and by making the liver release more glucose.2

The metformin label groups nicotinic acid with thiazide diuretics, corticosteroids, thyroid products, estrogens, oral contraceptives and some other drugs that tend to produce high blood sugar. It asks prescribers to watch for loss of control when such a drug is added, and for low blood sugar when it is withdrawn.1

How much niacin is involved

NIH says the effect is most likely at 1.5 g a day or more, an amount used only as a prescription medicine. The prescription niacin label says people with diabetes, or at risk of it, should be watched closely, especially in the first months of treatment or after a dose change.2,3

The sources do not describe what happens at the amounts in a multivitamin. That is not a finding either way, so tell your doctor about any supplement with niacin.

Other diabetes medicines

NIH's advice covers all diabetes medicines, not only metformin. Anyone taking one should have their blood sugar monitored if they take high-dose nicotinic acid, because their doses might need to change.2

What to ask your pharmacist

  • Does my supplement contain nicotinic acid, and how much?
  • Should I check my blood sugar more often if I start or stop it?
  • Do any of my other medicines also affect blood sugar?

Questions people ask

Does niacinamide affect blood sugar too?

The metformin label and NIH name nicotinic acid. The sources on this page do not address nicotinamide, also called niacinamide, so ask your pharmacist.1,2

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Sources

  1. Metformin hydrochloride tablets and extended-release tablets: prescribing information (Laurus Labs). DailyMed, U.S. National Library of Medicine. Revised July 2026. Opened 2026-10-07.
  2. National Institutes of Health, Office of Dietary Supplements. Niacin: Fact Sheet for Health Professionals. Updated November 18, 2022. Opened 2026-10-07.
  3. Niacin extended-release tablets: prescribing information and patient information (Amneal Pharmaceuticals). DailyMed, U.S. National Library of Medicine. Published September 18, 2026. Opened 2026-10-07.
  4. National Institutes of Health, Office of Dietary Supplements. Niacin: Fact Sheet for Consumers. Updated March 22, 2021. Opened 2026-10-07.

This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.