Drug & supplement interaction

Vitamin B12 + Metformin

Metformin brand names: Glucophage, Metformin.

Minor Interaction
Medically reviewed by · Updated October 2023
The bottom line Minor

Vitamin B12 has a minor interaction with Metformin. Metformin, a common medication used to manage type 2 diabetes, has been associated with lower vitamin B12 levels in some individuals.

Read the full interaction report
SeverityMinor
LikelihoodPossible
EvidenceA
What do Severity, Likelihood & Evidence mean?
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Interaction report

Vitamin B12 and Metformin

Here is the interaction we found between these two, with the evidence behind it.

Minor

Metformin (Glucophage)

Metformin, a common medication used to manage type 2 diabetes, has been associated with lower vitamin B12 levels in some individuals. Prolonged use of metformin can interfere with the absorption of B12 in the digestive system, potentially leading to a deficiency in this essential vitamin.
Severity Minor Likelihood Possible Evidence A

Interaction has been documented in animal or in lab research, or the interaction has been documented in humans but is limited to case reports or conflicting clinical research exists.

Dr. Brian Staiger, PharmD, BCPS
Dr. Brian Staiger explains PharmD, Clinical Pharmacist

Here's a helpful flip on the usual interaction story: in this case, it's the metformin that affects your vitamin B12, not the other way around. Over months and years of use, metformin can quietly reduce how much B12 your gut absorbs. For some people this slowly nudges B12 levels down, which can show up as tiredness, tingling or numbness in the hands and feet, or a certain type of anemia.

The good news is that taking a B12 supplement does not weaken how well metformin controls your blood sugar, so the two are fine together. This is well documented, but it's usually slow and not guaranteed to happen. Many doctors simply check B12 levels now and then. If you've been on metformin a long time, ask your pharmacist or doctor whether a B12 check makes sense for you.

Contact Dr. Brian directly if you have additional questions on this interaction

What These Ratings Mean

Every interaction above is graded three ways — here’s the key to each label.

Severity how clinically significant the interaction is
Major

Clinically significant. Avoid the combination, or use only under close professional supervision.

Moderate

Usually worth avoiding or managing — may need monitoring, a dose change, or timing apart.

Minor

Generally not serious. Be aware of it and mention it to your pharmacist.

Likelihood how strong the evidence is that the interaction actually happens in people
  • LikelyWell-controlled human studies have demonstrated the likely existence of this interaction.
  • ProbableInteraction has not been documented in well-controlled studies, however, the interaction has been demonstrated in some small human studies or in controlled animal studies in conjunction with multiple case reports.
  • PossibleInteraction has been documented in animal or in lab research, or the interaction has been documented in humans but is limited to case reports or conflicting clinical research exists.
  • UnlikelyInteraction has been demonstrated in animal or in lab research but has been shown not to occur in humans.
Evidence the quality of the studies behind the rating (graded A–D)
  • AHigh-quality meta-analysis (quantitative systematic review).
  • BCase-control study.
  • CConsensus.
  • DAnecdotal evidence.

These ratings are for information only. Never start, stop, or otherwise change your therapy before speaking with your provider.

Keep it in perspective

Vitamin B12 Also Interacts With Other Medications

Vitamin B12 has 19 minor known drug interactions in our database — the Metformin one above is one of them. If you take anything else, check it against the full list below.

Minor 19 No known interaction 2,811 (incl. Metformin)
Taking anything else?

Check Another of Your Medications Against Vitamin B12

Covers the 2,830 medications we’ve checked against Vitamin B12. Pick one to open its full report.

From our Q&A

Questions About Vitamin B12 or Metformin

These are real questions from readers, answered by the pharmacists at HelloPharmacist — written by a person, not generated from a database. Each one covers Vitamin B12 or Metformin, not necessarily both, but if one is close to what you were about to ask it will usually go further than a database entry can:

Not quite your question? Ask our pharmacists directly — it is free, there is no account required, and answers usually come back within 24 hours.

Everything else you take

See Every Supplement That Interacts With Metformin

This page covers Vitamin B12 only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Metformin page lists 258 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Siberian Cocklebur (major), Acai (moderate), African Wild Potato (moderate) and Agaricus Mushroom (moderate).

By severity: 2 major · 217 moderate · 39 minor.

From our pharmacist’s overview on the Metformin page

“Siberian cocklebur is the ingredient I most want anyone taking metformin (Glucophage) to know about. It has caused severe low blood sugar in people, documented in humans, and it should not be combined with any glucose-lowering medication.”

Reviewed by 2 · Jul 18, 2026

Open the Metformin interaction page

One more smart check

Taking Vitamin B12 as Part of a Dietary Supplement Product? Check It for Interactions

We hold 26,496 real supplement products containing Vitamin B12, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Vitamin B12. Your product may carry other ingredients that interact with Metformin too, on top of Vitamin B12 — and those would not show on this page. Find your product and we’ll check every ingredient on its label:

How much people look this up

Where Vitamin B12 and Metformin Sit Against Everything Else

Out of every supplement and medication people look up on HelloPharmacist, here is where these two land this week — and which way each has been moving.

Supplement Vitamin B12
Top 10

#7 of 1,452 supplements looked up here in the last 7 days

29 days ago today
Medication Metformin
Top 5%

#30 of 2,830 medications looked up here in the last 7 days

29 days ago today

Position among everything looked up on this site, not a measure of how commonly either one is used or how important it is. A supplement can climb this list because of a news story. It counts every request to the page, automated ones included, and nothing here identifies anyone.

Supplement

About Vitamin B12

What is Vitamin B12?

Vitamin B12
  • Treating or preventing B12 deficiency
  • Pernicious anemia
  • Low energy and fatigue
  • Nerve health and tingling/numbness
  • Support for vegetarians and vegans

Vitamin B12 (cobalamin) is an essential nutrient your body needs to make red blood cells, keep nerves healthy, and support DNA. Supplements are very helpful for people who are deficient — such as vegans, older adults, and those with absorption problems — but taking extra B12 when you are not deficient is unlikely to boost energy or health. Talk to your pharmacist or doctor if you think you may be low.

Read the full Vitamin B12 monograph & all interactions
Medication

About Metformin

What Is Metformin Used For?

Brand names: Glucophage, Metformin

Metformin is used to improve blood sugar (glucose) control in people with type 2 diabetes mellitus. It is always used together with diet and exercise, not instead of them.

Metformin hydrochloride tablets and oral solution are approved for adults and children 10 years and older. Metformin hydrochloride extended-release tablets — including brands such as Fortamet, Glumetza, and Metformin Hydrochloride Extended Release — are approved for adults only.

See full Metformin drug information
Keep checking

Other Drugs & Vitamin B12

Browse every other medication we’ve checked against Vitamin B12 — both the ones with a known interaction and the ones without. Select any drug for the full detail.

0Major
0Moderate
19Minor
2,810No known interaction
19 Minor 2,810 No interaction
Minor

19 interactions

No interaction 2,810 drugs checked — show the list

We also checked Vitamin B12 against these medications and found no known interaction in our sources. Open any page to confirm.

Showing the 60 most looked-up of 2,810 medications checked with no known interaction — see the full Vitamin B12 list.

See the full Vitamin B12 interactions page
See every supplement checked against Metformin, ranked by severity
Sources

Sources & How We Checked

Interaction details are evidence-graded and sourced from the Natural Medicines database. The medication overview comes from MedlinePlus.

Content is written and reviewed by licensed HelloPharmacist pharmacists. See our data sources and editorial standards for how this information is built and checked.

Parts of this content are provided by the Therapeutic Research Center, LLC.

DISCLAIMER: Currently this does not check for drug-drug interactions. This is not an all-inclusive comprehensive list of potential interactions and is for informational purposes only. Not all interactions are known or well-reported in the scientific literature, and new interactions are continually being reported. Input is needed from a qualified healthcare provider including a pharmacist before starting any therapy. Application of clinical judgment is necessary.

© 2021 Therapeutic Research Center, LLC

Keep exploring
Vitamin B12 monograph › Uses, safety, and every drug interaction in one place Metformin supplement interactions › Every supplement checked against Metformin, ranked by severity Metformin drug information › The full plain-English guide to this medication Supplement interaction checker › Check any supplement or product against your medications Browse medications A–Z › Every drug we've checked against herbs & supplements Ask a pharmacist › Free, personal answer from our licensed team
Pharmacist Counseling Corner

Taking Vitamin B12 and Metformin Together: Common Questions

Can you take Vitamin B12 with Metformin?
There is only a minor interaction, which is usually not serious. Read the full details on this page and confirm with your pharmacist before combining them.
How serious is the Vitamin B12 and Metformin interaction?
We rate it Minor. This interaction is generally not clinically significant, but it remains worth noting and discussing with your pharmacist.

Written and reviewed by the HelloPharmacist editorial staff. Our editorial policy

Still Have a Question About Metformin and Vitamin B12?

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This information is for education only and is not a substitute for professional medical advice. Always check with your pharmacist or doctor before starting, stopping, or combining supplements and medications.