Herb & supplement monograph

Vitamin B12 Drug Interactions, Uses, Effectiveness, Safety & More

Medically reviewed by Dr. Brian Staiger, PharmD, BCPS ·Updated July 2026

What is this page for?

First and foremost: how Vitamin B12 interacts with medications. The heart of this page is the interaction list — every drug Vitamin B12 is known to interact with, and how serious each one is.

But these pages have grown well beyond that into a full monograph — what Vitamin B12 is, what people use it for and how strong the evidence is, its safety and side effects, and answers to the questions we’re asked most — written and reviewed by the clinical staff at HelloPharmacist. It’s educational information from our licensed clinical databases, not medical advice, and we don’t sell or endorse products. Our editorial policy

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On this page

Vitamin B12 Drug Interactions: The Bottom Line

From the HelloPharmacist Editorial Team · Updated July 2026

Based on the available evidence, the overall risk of a clinically significant Vitamin B12 drug interaction appears low for most people. None of the roughly twenty interactions in this profile are rated major or even moderate, and every one is classified as minor.

Interactions deserving the most attention

The interaction worth knowing about runs in the opposite direction of what most people expect: it is not B12 changing how a medicine works, but a medicine lowering B12. Long-term use of metformin, a common type 2 diabetes drug, can interfere with B12 absorption in the gut and may lead to lower B12 levels over time. Human evidence here is still limited, so this is a reason for awareness in long-term metformin users rather than alarm.

What the rest of the list means

A list of twenty interactions can look worrying, but the number tells only part of the story. Because all of these are rated minor, the concern is generally about small shifts in vitamin levels rather than dangerous effects, and much of the supporting evidence is limited or preliminary. For most people, taking B12 alongside their medicines is unlikely to cause a meaningful problem.

Check your medications against Vitamin B12

Based on HelloPharmacist’s Vitamin B12 interaction data and reviewed under our editorial standards.

Interaction report

Drugs that interact with Vitamin B12

20 medications have a known interaction with Vitamin B12, graded by severity. Select any drug for the full evidence-based detail.

Don’t want to scroll the list? Just ask.

Tell us the medications you take and we’ll check each one against Vitamin B12 using our pharmacist-reviewed interaction data.

AI summaries are generated from our Vitamin B12 interaction data for education only — always confirm with your pharmacist. How we use AI

2,830 drugs

Read The List Like a Pharmacist

What Severity, Likelihood & Evidence Mean

Severity — How Serious It Can Be

Major. Clinically significant; generally best avoided, or used only under direct professional supervision.
Moderate. May need monitoring, a dose adjustment, or separating the times you take each one.
Minor. Generally not clinically significant, but still worth noting and mentioning to your pharmacist.
No known interaction. Checked against our sources with nothing documented — not the same as proven safety.

Likelihood — How Well It’s Documented

Likely. Well-controlled human studies have demonstrated the likely existence of this interaction
Probable. Interaction 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.
Possible. 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
Unlikely. Interaction has been demonstrated in animal or in lab research but has been shown not to occur in humans.

Where This Data Comes From

Interaction records are evidence-graded and sourced from the Natural Medicines database (TRC Healthcare), the same reference used by pharmacists and hospitals.
Each drug listed above links to the full report for that exact Vitamin B12 combination — clinical detail, likelihood, evidence level, and citations.
Content is reviewed by licensed HelloPharmacist pharmacists — see our data sources and editorial standards.

The big picture

The kinds of drugs Vitamin B12 affects

Every type of medication (drug category) Vitamin B12 is known to interact with. Open any category for the detail — or search your exact drug in the checker above.

All 1 drug category Vitamin B12 interacts with

Metformin (glucophage)

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.

Likelihood Possible Evidence A

Monograph

Vitamin B12: Uses, Safety & Side Effects

Medically reviewed by Dr. Brian Staiger, PharmD, BCPS · Reviewed July 2026 ·

The bottom line

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.

Part used: Not applicable (a vitamin, not a plant part)
Common forms: Tablets, capsules, sublingual (under-the-tongue) tablets, lozenges, liquid drops, nasal spray, and injections

People commonly use it for

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

Popular and traditional uses — not proof it works. See “Uses & effectiveness” below for the evidence.

Safety at a glance

OverallLikely safe

B12 is generally very safe and has no established upper limit because excess is removed in the urine.

PregnancyLikely Safe

When used orally in amounts that do not exceed the recommended dietary allowance (RDA). The RDA for vitamin B12 during pregnancy is 2.6 mcg daily. The...

Read the full pregnancy detail

BreastfeedingLikely Safe

When used orally in amounts that do not exceed the recommended dietary allowance (RDA). The RDA of vitamin B12 during lactation is 2.8 mcg daily. Ther...

Read the full breastfeeding detail

Pregnancy & breastfeeding ratings are from Natural Medicines (Therapeutic Research Center). Safety guidance is general; always confirm with your pharmacist or doctor for your situation.

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Overview

Vitamin B12, also called cobalamin, is a water-soluble vitamin your body needs but cannot make on its own. It is naturally found in animal-based foods such as meat, fish, poultry, eggs, and dairy. Some foods, like certain breakfast cereals and plant-based milks, are fortified with added B12.

Your body uses B12 to make red blood cells, keep your nervous system working, and help build DNA. Because plants do not naturally contain B12, people who follow vegan or strict vegetarian diets are at higher risk of running low and often need a supplement or fortified foods.

B12 comes in several forms, including cyanocobalamin and methylcobalamin. It is available as tablets, under-the-tongue (sublingual) tablets, liquids, nasal sprays, and as injections given by a healthcare provider for more serious deficiency.

How it works

Vitamin B12 acts as a helper (a coenzyme) for important chemical reactions in the body. It is needed to make healthy red blood cells, and without enough B12, red blood cells become large and abnormal, leading to a type of anemia.

B12 also helps make and maintain myelin, the protective coating around nerve fibers. This is why a long-term deficiency can cause nerve problems such as numbness, tingling, balance issues, and memory trouble.

In addition, B12 works closely with folate to support DNA production and to process an amino acid called homocysteine. To be absorbed from food, B12 needs a protein made in the stomach called intrinsic factor. When this process is broken, deficiency can develop even with a normal diet.

Effectiveness

Does Vitamin B12 work?

Here’s what the research actually shows for each use — graded by Natural Medicines and reviewed by Dr. Brian Staiger, PharmD.

Evidence overview · 59 uses evaluated

2 Effective 1 Likely effective 3 Possibly effective 8 Leans ineffective 45 Insufficient evidence

How to read these evidence grades

Natural Medicines’ 7-point scale. We show each rating’s label word-for-word.

1EffectiveStrong, consistent evidence it works.

2Likely EffectiveGood evidence, though not yet conclusive.

3Possibly EffectiveSome evidence suggests a benefit.

4Possibly IneffectiveSome evidence it may not help.

5Likely IneffectiveFairly strong evidence it doesn’t help.

6IneffectiveStrong evidence it doesn’t work.

7Insufficient Reliable Evidence to RateToo little research to say either way.

Effective Imerslund-Grasbeck disease