Skip to content

Coming soon. The store is not open yet.

Menu
Full Measure

Medicines and supplements

B complex and 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 says metformin may lower vitamin B12 levels, reports B12 falling below normal in about 7% of people in 29-week trials, and recommends measuring B12 every 2 to 3 years. A B complex can contain B12, and products differ in how much.1,2

Key facts

  • The metformin label says metformin may lower vitamin B12 levels, and that B12 fell below normal in about 7% of people in 29-week trials.1
  • The label tells prescribers to measure B12 every 2 to 3 years in people who take metformin.1
  • NIH says B complex supplements generally contain 50 to 500 mcg of B12, compared with 5 to 25 mcg in a typical multivitamin.3
  • NIH says the share of B12 absorbed falls as the amount rises: about 50% at 1 to 2 mcg or less and about 2% at 500 mcg.3
  • Products differ in which B vitamins they include, so the Supplement Facts panel is the only way to know what a given B complex supplies.2,3
  • Many B complexes also contain folic acid, and NIH says large amounts of folic acid can correct the anemia of low B12 while nerve damage continues.4,5

Your doctor may want to check on you

Metformin may lower vitamin B12 levels, possibly by reducing its absorption. The metformin label recommends measuring vitamin B12 every 2 to 3 years in people who take it.1,3

On the medicine's label

Why does metformin lower vitamin B12?

MedlinePlus describes metformin as a medicine used alone or with others for type 2 diabetes. It asks people to tell their doctor and pharmacist about all vitamins and supplements they take, and to mention any past low vitamin B12.6

The metformin label says the drop to below-normal B12 was seen in about 7% of people whose levels had been normal, in trials lasting 29 weeks. It suggests the cause may be interference with absorbing B12 from the B12-intrinsic factor complex. It says people with inadequate B12 or calcium intake or absorption appear more likely to be affected, and tells prescribers to measure blood counts every year and B12 at 2 to 3 year intervals.1

NIH's professional fact sheet says metformin might reduce B12 absorption and significantly reduce blood B12 levels.3

What does a B complex add for someone taking metformin?

A B complex combines several of the eight B vitamins in one product, and B12 is only one of them. NIH says B complex supplements generally contain 50 to 500 mcg of B12, against 5 to 25 mcg in a typical multivitamin.3

NIH also says the share of B12 absorbed falls as the amount rises: about 50% at 1 to 2 mcg or less, about 2% at 500 mcg and 1.3% at 1,000 mcg. The number on the label is therefore not the amount that reaches the blood.3

Products differ in which B vitamins they include and how much of each they contain, so the Supplement Facts panel is the only way to know what a given B complex supplies.2,3

The sources do not say whether a B complex changes what the metformin label describes, or how the label's B12 checks should be read for someone who takes one. That is a question for your doctor, who can see your test results.

Why does folic acid in a B complex matter with low B12?

Large amounts of folic acid can correct the anemia caused by a vitamin B12 deficiency while the nerve damage continues, which can delay the diagnosis, and may make the deficiency worse. This is the basis of the upper limit for folic acid.4,5

The metformin label asks prescribers to follow both blood counts and B12. For a person on metformin, a B complex that contains folic acid is one more thing the doctor needs to know about.1

What else can lower vitamin B12?

Your doctor may want to check on you

Daily use of acid-reducing medicines such as omeprazole over a long time, for example more than 3 years, can reduce how much vitamin B12 the body absorbs from food. The omeprazole label notes rare reports of B12 deficiency.3,7

On the medicine's label

NIH names acid-reducing medicines and metformin together as medicines that can lower B12, so people who take both should mention both.3

What to ask your pharmacist about a B complex and metformin

  • When was my vitamin B12 last measured, and when is the next check due?
  • Does my B complex contain B12 and folic acid, and how much of each?
  • Do I also take an acid reducer, which NIH names as another cause of low B12?3
  • Does my B complex contain biotin, which can affect some lab tests?8,9
  • Should my doctor see the label of my B complex before my next blood test?

Questions people ask

Can I take B complex and metformin together?

The metformin label's concern is that metformin may lower B12, not that the two interfere with each other. Ask your pharmacist how your B complex fits with the B12 checks the label describes.1

Do B vitamins interact with metformin?

The documented effect runs from the medicine to the vitamin: metformin may lower B12. The sources on this page name vitamin B12, not the other B vitamins.1,3

Should I take a super B complex with metformin?

The sources checked do not give advice to take one. Products differ in what they contain, so check the Supplement Facts panel and ask your doctor whether your B12 level should be measured.2,3

What B vitamins does metformin deplete?

The metformin label names vitamin B12. The sources on this page do not say that metformin lowers the other B vitamins, which is not a finding either way.1

See what we make

Every product shows its whole label and what its lab report covers. The store opens soon.

See the Full Measure line

Sources

  1. Metformin hydrochloride tablets and extended-release tablets: prescribing information (Laurus Labs Limited). DailyMed, U.S. National Library of Medicine. Published September 28, 2026. Opened 2026-10-07.
  2. National Institutes of Health, Office of Dietary Supplements. Vitamin B12: Fact Sheet for Consumers. Updated December 15, 2023. Opened 2026-10-07.
  3. National Institutes of Health, Office of Dietary Supplements. Vitamin B12: Fact Sheet for Health Professionals. Updated July 2, 2025. Opened 2026-10-07.
  4. National Institutes of Health, Office of Dietary Supplements. Folate: Fact Sheet for Health Professionals. Updated November 30, 2022. Opened 2026-10-07.
  5. National Institutes of Health, Office of Dietary Supplements. Folate: Fact Sheet for Consumers. Updated November 1, 2022. Opened 2026-10-07.
  6. MedlinePlus. Metformin. U.S. National Library of Medicine. Last revised February 15, 2024. Opened 2026-10-11.
  7. Omeprazole delayed-release capsules: prescribing information (Preferred Pharmaceuticals Inc.). DailyMed, U.S. National Library of Medicine. Published September 28, 2026. Opened 2026-10-07.
  8. National Institutes of Health, Office of Dietary Supplements. Biotin: Fact Sheet for Health Professionals. Updated January 10, 2022. Opened 2026-10-07.
  9. U.S. Food and Drug Administration. Testing for Biotin Interference in In Vitro Diagnostic Devices: Guidance for Industry. October 2020. Opened 2026-10-07.

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