Can Metformin Cause Vitamin B12 Deficiency? Symptoms, Risks, Prevention & What to Do

✍️ Written by Dimitar Georgiev Atanasov, MPharm
Master Pharmacist | Medication Safety Educator
Bulgarian Pharmaceutical Union (BPhU)
UIN: 0210000586

👨‍⚕️ Medical Review by Dr. Tania Georgieva-Stoianova, MD
General Practitioner
25+ Years of Clinical Experience
Actively Practicing Physician
UIN: 2900000451

💊 Pharmacy & Scientific Review by Gergana Krasimirova Atanasova, MPharm
Assistant Lecturer, Faculty of Pharmacy
University “Prof. Dr. Asen Zlatarov” – Burgas
Master Pharmacist
Bulgarian Pharmaceutical Union (BPhU)
UIN: 0210000587

Quick Answer – Can Metformin Cause Vitamin B12 Deficiency?

Can Metformin Cause Vitamin B12 Deficiency? Yes. Metformin can cause vitamin B12 deficiency, especially when it is taken for several years or at higher daily doses. Not everyone who takes metformin develops low vitamin B12 levels, but long-term treatment is a well-recognized risk factor acknowledged by medical guidelines and regulatory agencies.

Vitamin B12 deficiency often develops slowly and may initially cause no symptoms. As levels continue to fall, people may experience fatigue, weakness, numbness or tingling in the hands and feet, balance problems, memory difficulties, or anemia. Fortunately, routine monitoring and appropriate vitamin B12 supplementation can usually prevent serious complications without requiring patients to stop taking metformin.

---

Physician Quick Take

Most people should not stop metformin simply because they are concerned about vitamin B12 deficiency. Instead, physicians often recommend periodic vitamin B12 testing for patients taking metformin long term—particularly those with symptoms such as fatigue, numbness, or unexplained anemia. When detected early, vitamin B12 deficiency is usually easy to treat while allowing metformin therapy to continue safely.

---

Pharmacist Quick Take

Community pharmacists frequently counsel patients who have heard that metformin “uses up” vitamin B12. The reality is more nuanced. Metformin does not destroy vitamin B12, but it can reduce its absorption in the intestine over time. Understanding this difference helps patients recognize why monitoring is important without becoming unnecessarily worried about taking an effective medication.

---

Key Takeaways

✔ Metformin is one of the few commonly prescribed medications consistently linked to vitamin B12 deficiency.

✔ The risk generally increases with long-term treatment, higher doses, and advancing age.

✔ Vitamin B12 deficiency may contribute to fatigue, weakness, numbness, tingling, balance problems, memory changes, and anemia.

✔ Many people with low vitamin B12 levels have no symptoms initially, making routine monitoring valuable.

✔ Most patients can continue taking metformin while treating vitamin B12 deficiency if it develops.

✔ Never stop metformin without discussing it with your healthcare provider.

---

Why Do Patients Ask This Question?

Many patients first learn about the connection between metformin and vitamin B12 after reading the medication leaflet, hearing about it on social media, or being told by another patient.

Others begin searching after developing symptoms such as:

• Persistent tiredness
• Low energy
• Tingling in the feet
• Numb fingers
• Poor balance
• Difficulty concentrating
• Memory problems
• Unexplained anemia

Because these symptoms can have many different causes, people naturally wonder whether metformin is responsible.

This question has become even more common in recent years because medical organizations increasingly recommend that healthcare professionals consider vitamin B12 deficiency in patients receiving long-term metformin therapy.

---

Can Metformin Really Cause Vitamin B12 Deficiency?

The short answer is yes.

Unlike many medication side effects that remain controversial, the association between metformin and vitamin B12 deficiency is supported by decades of clinical research.

Multiple observational studies, randomized clinical trials, and systematic reviews have shown that people taking metformin are more likely to develop reduced vitamin B12 levels than people who are not taking the medication.

For this reason, several professional organizations now recommend considering periodic vitamin B12 assessment in patients receiving long-term metformin treatment, particularly if symptoms suggest deficiency.

Importantly, this does not mean that metformin is unsafe.

Metformin remains one of the safest and most effective first-line medications for type 2 diabetes. Its proven benefits—including improved blood glucose control, cardiovascular advantages in appropriate patients, and a long history of safe use—generally outweigh the relatively manageable risk of vitamin B12 deficiency.

The key message is not to fear metformin but to understand one of its well-recognized long-term effects so that it can be identified and treated early if necessary.

---

How Common Is Vitamin B12 Deficiency in People Taking Metformin?

One of the most common misconceptions is that everyone taking metformin will eventually become vitamin B12 deficient.

Fortunately, this is not true.

Research suggests that the frequency varies considerably depending on:

• Daily metformin dose
• Duration of treatment
• Patient age
• Dietary vitamin B12 intake
• Existing gastrointestinal conditions
• Individual absorption differences

Some studies report relatively low rates of deficiency, while others identify much higher numbers among patients taking metformin for many years.

This variation explains why healthcare providers do not automatically prescribe vitamin B12 supplements to every patient starting metformin. Instead, they assess each person’s individual risk factors and monitor appropriately.

---

Table: Factors That Increase the Risk of Vitamin B12 Deficiency

Risk Factor	Why It Matters
Long-term metformin therapy	Reduced vitamin B12 absorption accumulates over time
Higher daily doses	Greater exposure may increase the risk
Older age	Natural vitamin B12 absorption declines with aging
Vegetarian or vegan diet	Lower dietary intake of vitamin B12
Previous gastrointestinal surgery	Reduced absorption capacity
Digestive disorders	Conditions affecting the small intestine may worsen deficiency
Poor nutritional status	Lower vitamin B12 stores before treatment begins

Importantly, many patients have several of these risk factors simultaneously, increasing the likelihood of developing deficiency over time.

---

Does Metformin Destroy Vitamin B12?

No.

This is one of the biggest myths surrounding metformin.

The medication does not destroy vitamin B12, remove it from the bloodstream, or permanently damage the body’s vitamin stores.

Instead, researchers believe metformin primarily affects how vitamin B12 is absorbed in the final part of the small intestine.

Although scientists continue studying the exact biological mechanisms, the overall effect is well established:

Over many months or years, less vitamin B12 may be absorbed from food, gradually reducing the body’s stored supply.

Because the liver stores several years’ worth of vitamin B12, deficiency usually develops slowly rather than suddenly.

This gradual progression explains why many people take metformin for years before noticing any symptoms.

How Does Metformin Reduce Vitamin B12 Absorption?

Although researchers are still investigating the exact mechanism, most evidence suggests that metformin interferes with the absorption of vitamin B12 in the last part of the small intestine, known as the ileum.

Normally, vitamin B12 from food binds to a protein called intrinsic factor. This complex then travels to the ileum, where specialized receptors absorb the vitamin into the bloodstream.

Metformin appears to reduce the efficiency of this absorption process. One proposed explanation is that it alters calcium-dependent uptake of the intrinsic factor–vitamin B12 complex, making absorption less effective over time.

Importantly, metformin does not completely block vitamin B12 absorption. Instead, it gradually reduces the amount absorbed from food. Because the liver stores large amounts of vitamin B12, it often takes several years before those stores become depleted enough to produce symptoms.

This explains why many people can take metformin for a long time without noticing any problems before deficiency eventually develops.

---

Why Is Vitamin B12 So Important?

Vitamin B12 is an essential nutrient involved in numerous functions throughout the body.

It plays a critical role in:

• Red blood cell production
• DNA synthesis
• Healthy nerve function
• Brain health
• Energy metabolism
• Cell division

Without enough vitamin B12, the body cannot produce healthy red blood cells efficiently, and nerve cells may gradually become damaged.

This is why vitamin B12 deficiency can affect many different organ systems rather than causing just one symptom.

---

What Symptoms Can Vitamin B12 Deficiency Cause?

One of the challenges with vitamin B12 deficiency is that symptoms usually develop slowly.

At first, people may simply feel “not quite right.”

Common early symptoms include:

• Persistent fatigue
• Low energy
• Weakness
• Reduced exercise tolerance
• Difficulty concentrating
• Mild memory problems
• Irritability

As deficiency progresses, neurological symptoms may appear.

These include:

• Numbness in the hands
• Numbness in the feet
• Tingling (“pins and needles”)
• Burning sensations
• Poor balance
• Difficulty walking
• Muscle weakness

Some people also develop megaloblastic anemia, which can further worsen fatigue and shortness of breath.

---

Table: Early vs Advanced Symptoms of Vitamin B12 Deficiency

Early Symptoms	More Advanced Symptoms
Fatigue	Significant numbness
Low energy	Difficulty walking
Weakness	Poor balance
Reduced concentration	Memory impairment
Mild dizziness	Peripheral neuropathy
Irritability	Megaloblastic anemia

Not everyone experiences every symptom, and symptoms often develop gradually over months or years.

---

Can Vitamin B12 Deficiency Explain Fatigue?

Yes.

Fatigue is one of the most common manifestations of vitamin B12 deficiency.

There are several reasons why this occurs.

First, inadequate vitamin B12 can impair normal red blood cell production. Fewer healthy red blood cells means less oxygen is delivered to tissues throughout the body.

Second, vitamin B12 plays an important role in normal nerve function and cellular metabolism. When levels fall, many people describe:

• Constant tiredness
• Feeling exhausted after minimal activity
• Difficulty staying focused
• Lack of motivation
• General weakness

However, fatigue has many possible causes.

Even if you are taking metformin, tiredness could also be related to:

• Poor blood glucose control
• Sleep disorders
• Iron deficiency
• Thyroid disease
• Depression
• Chronic illness
• Other medications

This is why healthcare professionals usually evaluate fatigue rather than assuming metformin is always responsible.

---

Can Vitamin B12 Deficiency Cause Numbness or Tingling?

Absolutely.

This is one of the most clinically important complications of vitamin B12 deficiency.

Vitamin B12 helps maintain the protective covering surrounding nerves, known as the myelin sheath.

When vitamin B12 levels become too low, nerve function can gradually deteriorate.

Patients often describe sensations such as:

• Tingling in the toes
• Tingling in the fingers
• Burning feet
• Electric shock sensations
• Reduced sensation
• Difficulty feeling the ground while walking

These symptoms are collectively referred to as peripheral neuropathy.

Unfortunately, diabetes itself can also cause peripheral neuropathy.

This creates an important diagnostic challenge.

If someone with diabetes develops numbness while taking metformin, healthcare professionals must determine whether the symptoms are caused by:

• diabetic neuropathy,
• vitamin B12 deficiency,
• another neurological condition,
• or a combination of factors.

For this reason, checking vitamin B12 levels may become an important part of the evaluation.

---

Can Vitamin B12 Deficiency Affect Memory and Brain Function?

Yes.

Vitamin B12 is essential for normal neurological function.

Although severe cognitive impairment is uncommon, prolonged deficiency may contribute to:

• Difficulty concentrating
• Forgetfulness
• Slower thinking
• Brain fog
• Reduced attention
• Mood changes

Older adults may be particularly vulnerable because both aging and long-term metformin therapy can increase the likelihood of vitamin B12 deficiency.

These symptoms usually improve when the deficiency is recognized and treated early.

However, prolonged untreated deficiency increases the risk that neurological damage may become only partially reversible.

---

Table: Why Vitamin B12 Matters

Body System	Possible Effects of Vitamin B12 Deficiency
Blood	Megaloblastic anemia
Nervous system	Numbness, tingling, neuropathy
Brain	Memory problems, brain fog, poor concentration
Muscles	Weakness, fatigue
Balance	Unsteady walking, falls

---

Who Is Most Likely to Develop Vitamin B12 Deficiency While Taking Metformin?

Although anyone taking metformin can develop vitamin B12 deficiency, certain groups are at higher risk.

These include people who:

• Have taken metformin for several years
• Take higher daily doses
• Are over the age of 60
• Follow vegetarian or vegan diets
• Have gastrointestinal disorders such as Crohn’s disease or celiac disease
• Have previously undergone stomach or intestinal surgery
• Take medications that also reduce vitamin B12 absorption, such as proton pump inhibitors (PPIs)

The presence of multiple risk factors increases the likelihood that vitamin B12 stores will gradually decline over time.

---

Does Everyone Taking Metformin Need Vitamin B12 Supplements?

No.

This is another common misconception.

Most healthcare professionals do not recommend routine vitamin B12 supplementation for every patient taking metformin.

Instead, supplementation is usually considered when:

• Blood tests confirm low vitamin B12 levels
• Symptoms strongly suggest deficiency
• Patients belong to a high-risk group
• Previous deficiency has already been diagnosed

Taking unnecessary supplements without medical advice is generally not recommended, even though vitamin B12 is considered relatively safe.

The best approach is individualized care based on symptoms, risk factors, and laboratory results rather than assuming that every person taking metformin requires supplementation.

Should Everyone Taking Metformin Have Their Vitamin B12 Levels Checked?

This is one of the most common questions patients ask after learning about the connection between metformin and vitamin B12 deficiency.

The answer is not necessarily but many people can benefit from periodic assessment.

Most medical organizations do not recommend routine vitamin B12 testing for every patient immediately after starting metformin. However, they do recommend considering vitamin B12 measurement in people receiving long-term treatment, especially if they develop symptoms suggestive of deficiency.

Your healthcare provider may recommend testing if you experience:

• Persistent fatigue
• Unexplained weakness
• Numbness or tingling in the hands or feet
• Poor balance
• Memory problems
• Difficulty concentrating
• Megaloblastic anemia
• Peripheral neuropathy

Testing becomes even more important if you have additional risk factors such as older age, gastrointestinal disorders, or a vegetarian or vegan diet.

The goal is to identify deficiency before permanent complications develop.

---

How Is Vitamin B12 Deficiency Diagnosed?

Vitamin B12 deficiency cannot be diagnosed based on symptoms alone.

Many symptoms overlap with:

• Diabetes itself
• Thyroid disease
• Iron deficiency
• Depression
• Chronic kidney disease
• Sleep disorders
• Other neurological conditions

For this reason, healthcare professionals usually confirm deficiency through laboratory testing.

Common tests include:

• Serum vitamin B12 level
• Complete blood count (CBC)
• Mean corpuscular volume (MCV)
• Methylmalonic acid (when appropriate)
• Homocysteine level (selected patients)

These results help determine whether symptoms are truly related to vitamin B12 deficiency or another medical condition.

---

How Often Should Vitamin B12 Be Checked?

There is no single schedule that applies to every patient.

Instead, testing frequency depends on individual risk factors.

For many patients taking metformin, healthcare providers may consider periodic vitamin B12 assessment after several years of treatment.

Patients at higher risk may require more frequent monitoring.

Your doctor may recommend earlier testing if you:

• Develop neurological symptoms
• Experience unexplained fatigue
• Have anemia
• Take high-dose metformin
• Have digestive disorders affecting absorption
• Have previously been diagnosed with vitamin B12 deficiency

Rather than following a fixed calendar, clinicians usually individualize monitoring based on the patient’s overall health.

---

Table: Who May Benefit Most from Vitamin B12 Testing?

Patient Group	Why Testing May Be Helpful
Long-term metformin users	Risk increases over time
Older adults	Reduced absorption with aging
People with fatigue	Deficiency may contribute to symptoms
Patients with numbness or tingling	Evaluate for possible neuropathy
Vegetarians and vegans	Lower dietary vitamin B12 intake
Patients with anemia	Vitamin B12 deficiency is a possible cause
Gastrointestinal disorders	Reduced absorption may increase risk

Testing is relatively simple and may help identify deficiency before serious complications develop.

---

Can Vitamin B12 Deficiency Be Prevented?

In many cases, yes.

Although metformin may reduce vitamin B12 absorption, deficiency is often preventable through early recognition and appropriate management.

Preventive strategies include:

• Following a balanced diet
• Attending regular medical appointments
• Reporting new neurological symptoms promptly
• Undergoing vitamin B12 testing when recommended
• Taking supplements only if advised by your healthcare provider

The key is awareness rather than fear.

Most patients taking metformin never develop severe complications because deficiency is identified and treated before permanent damage occurs.

---

Foods Naturally Rich in Vitamin B12

Vitamin B12 is found almost exclusively in foods of animal origin.

Excellent dietary sources include:

• Beef
• Liver
• Salmon
• Tuna
• Sardines
• Eggs
• Milk
• Cheese
• Yogurt

Some breakfast cereals and plant-based milk alternatives are also fortified with vitamin B12.

However, increasing dietary intake alone may not fully correct deficiency if intestinal absorption has already been significantly reduced.

---

Table: Good Dietary Sources of Vitamin B12

Food	Naturally Rich in Vitamin B12
Beef liver	Excellent source
Beef	Excellent source
Salmon	Excellent source
Tuna	Excellent source
Sardines	Excellent source
Eggs	Good source
Milk	Good source
Cheese	Good source
Yogurt	Good source
Fortified breakfast cereals	Variable amounts

A healthy diet remains important, but some patients may still require supplementation depending on laboratory results.

---

Vitamin B12 Tablets or Injections: Which Is Better?

Many patients worry that vitamin B12 injections are always necessary.

Fortunately, this is not the case.

Treatment depends on:

• Severity of deficiency
• Presence of neurological symptoms
• Underlying cause
• Physician preference
• Individual patient factors

For mild deficiency, oral vitamin B12 supplements may be sufficient.

More severe deficiency—particularly when neurological symptoms are present may require injectable vitamin B12 to restore body stores more rapidly.

Your healthcare provider will recommend the most appropriate treatment based on your individual circumstances.

---

Can You Continue Taking Metformin If You Develop Vitamin B12 Deficiency?

In most cases, yes.

One of the biggest misconceptions is that low vitamin B12 automatically means metformin must be discontinued.

For most patients, this is unnecessary.

Instead, healthcare providers usually:

• Confirm vitamin B12 deficiency
• Treat the deficiency appropriately
• Continue monitoring symptoms
• Reassess vitamin B12 levels over time
• Continue metformin if it remains clinically beneficial

Because metformin provides substantial benefits for blood glucose control and long-term diabetes management, correcting vitamin B12 deficiency is usually preferred over discontinuing an otherwise effective medication.

Only your healthcare provider can determine whether changes to your treatment plan are appropriate.

---

Can Vitamin B12 Levels Return to Normal?

Yes.

When vitamin B12 deficiency is recognized early and treated appropriately, blood levels often return to normal.

Many patients also notice improvement in symptoms such as:

• Fatigue
• Weakness
• Reduced concentration
• Mild numbness
• Tingling

Recovery depends on several factors, including:

• How long deficiency has been present
• Severity of deficiency
• Presence of nerve damage
• Underlying medical conditions
• Adherence to treatment

The earlier deficiency is identified, the greater the likelihood of complete recovery.

---

Can Permanent Nerve Damage Occur?

Unfortunately, it can.

This is why vitamin B12 deficiency should never be ignored.

Prolonged deficiency may lead to irreversible nerve injury in some individuals.

Potential long-term complications include:

• Persistent numbness
• Chronic tingling
• Difficulty walking
• Poor balance
• Reduced sensation
• Ongoing peripheral neuropathy

Fortunately, these complications are far less likely when deficiency is recognized and treated promptly.

Early diagnosis remains the best strategy for preventing permanent neurological damage.

Physician Takeaway

Metformin remains one of the most effective and extensively studied medications for the treatment of type 2 diabetes. Although long-term use has been associated with vitamin B12 deficiency, this potential adverse effect is generally manageable through appropriate monitoring and treatment.

Patients should not discontinue metformin solely because they are concerned about vitamin B12 deficiency. Instead, individuals who develop symptoms such as persistent fatigue, numbness, tingling, balance problems, or unexplained anemia should discuss vitamin B12 testing with their healthcare provider.

Early recognition and treatment of deficiency can prevent neurological complications while allowing most patients to continue benefiting from metformin therapy.

---

Pharmacist Takeaway

Community pharmacists frequently counsel patients who worry after reading that metformin can “cause vitamin B12 deficiency.”

The most important point to remember is that this effect develops gradually rather than suddenly. Most patients taking metformin never experience severe vitamin B12 deficiency, especially when regular medical follow-up is maintained.

If you have been taking metformin for several years, particularly at higher doses, and begin noticing symptoms such as unusual tiredness, tingling, or weakness, it is reasonable to ask your healthcare provider whether vitamin B12 testing is appropriate.

Simple monitoring today may help prevent more significant health problems in the future.

---

Clinical Evidence

The association between metformin and reduced vitamin B12 levels has been consistently demonstrated in clinical research spanning several decades.

Multiple observational studies, randomized clinical trials, systematic reviews, and meta-analyses have shown that long-term metformin therapy can reduce vitamin B12 absorption and increase the likelihood of biochemical vitamin B12 deficiency.

Because of this evidence, regulatory agencies and professional medical organizations—including the UK Medicines and Healthcare products Regulatory Agency (MHRA)—recommend considering vitamin B12 testing in patients receiving long-term metformin treatment who develop symptoms suggestive of deficiency or possess additional risk factors.

Current evidence supports awareness and monitoring rather than discontinuation of metformin in most patients.

---

Table: Common Myths About Metformin and Vitamin B12

Myth	Reality
Everyone taking metformin develops vitamin B12 deficiency.	Most patients do not develop clinically significant deficiency.
Metformin destroys vitamin B12.	Metformin primarily reduces vitamin B12 absorption over time.
Vitamin B12 deficiency develops immediately.	It usually develops gradually over several years.
Low vitamin B12 means you must stop metformin.	Most patients can continue metformin while treating the deficiency.
Fatigue always means vitamin B12 deficiency.	Fatigue has many possible causes and requires proper evaluation.
Vitamin B12 injections are always required.	Many patients respond well to oral supplementation, depending on the severity and cause of deficiency.

---

Bottom Line

Yes, metformin can contribute to vitamin B12 deficiency, particularly during long-term treatment or at higher daily doses. However, this does not mean that everyone taking metformin will develop deficiency or that the medication should be stopped.

The most important message is awareness.

Vitamin B12 deficiency often develops slowly and may initially cause no symptoms. When symptoms do occur, they commonly include fatigue, weakness, numbness, tingling, poor balance, memory difficulties, or anemia.

Fortunately, vitamin B12 deficiency is usually easy to detect through laboratory testing and, in most cases, can be successfully treated while allowing patients to continue benefiting from metformin therapy.

If you have concerns about vitamin B12 deficiency, discuss them with your physician or pharmacist rather than making changes to your medication on your own.

---

Frequently Asked Questions – Can Metformin Cause Vitamin B12 Deficiency

---

Related Guides

Continue learning about metformin with these evidence-based guides:

• Why Am I Tired After Taking Metformin?
• Can Metformin Cause Brain Fog?
• Can Metformin Cause Anxiety?
• Can Metformin Cause Hair Loss?
• Can Metformin Cause Diarrhea?
• Why Does Metformin Cause Diarrhea?
• Can Metformin Cause Metallic Taste?
• Can Metformin Cause Weakness?
• Can Metformin Cause Numbness?
• What Is Metformin? (Pillar Guide)

---

Medical Disclaimer

The information provided in this article is intended for educational purposes only and should not replace professional medical advice, diagnosis, or treatment. Always consult your physician, pharmacist, or another qualified healthcare professional regarding your medications and individual medical condition.

---

Sources

• American Diabetes Association. Standards of Care in Diabetes.
• National Institute for Health and Care Excellence (NICE). Type 2 Diabetes Guidelines.
• U.S. Food and Drug Administration (FDA). Metformin Prescribing Information.
• UK Medicines and Healthcare products Regulatory Agency (MHRA). Metformin and Reduced Vitamin B12 Levels: New Advice for Monitoring Patients at Risk.
• National Institutes of Health (NIH) – Office of Dietary Supplements. Vitamin B12 Fact Sheet for Health Professionals.
• PubMed. Clinical studies on metformin-associated vitamin B12 deficiency.
• Cochrane Library.
• European Medicines Agency (EMA).
• British National Formulary (BNF).

---

Image Disclosure – Can Metformin Cause Vitamin B12 Deficiency?

Some images used in this article are original illustrations or AI-generated educational graphics created to improve understanding of medical concepts. They are intended for informational purposes only and do not depict actual patients or clinical situations.