Quick answer: Yes. Metformin can lower vitamin B12 levels, particularly with longer use, higher doses or other risk factors for deficiency. That does not mean everyone taking metformin has low B12. If you develop unusual fatigue, pins and needles, a sore tongue or anaemia, ask your healthcare professional whether a B12 test belongs in your assessment. Do not stop metformin on your own.
It is easy to put tiredness or tingling down to diabetes, age or a busy schedule. But when you take metformin, vitamin B12 is another possible piece of the picture. B12 helps keep nerves and blood cells healthy. The UK Medicines and Healthcare products Regulatory Agency (MHRA) advises testing when deficiency is suspected and considering periodic monitoring for people with risk factors.
Anthony Ofori | Medical Graduate in General Medicine | Founder, WellNest Central
Last updated: 26 September 2026
How does metformin affect vitamin B12?
Metformin helps manage blood sugar, but it can also interfere with vitamin B12 absorption and reduce the level measured in blood. The risk tends to increase with higher doses and longer treatment, although a person’s diet, age and other medical conditions also matter. The NIH Office of Dietary Supplements lists metformin among medicines that can reduce B12 absorption and blood levels.
Metformin remains an important treatment for many people. A possible B12 problem is usually a reason to assess and, when necessary, correct B12 while continuing the prescribed diabetes plan. The MHRA specifically advises people not to stop metformin without speaking to their doctor.
Which symptoms are worth mentioning?
- New or worsening tiredness that feels out of proportion to your usual day.
- Pins and needles, numbness or changes in sensation in the feet or hands.
- A sore, red tongue, mouth discomfort or pale or yellowish skin.
- Weakness, balance changes or trouble concentrating, especially if symptoms are progressing.
These clues are not specific to B12 deficiency. Diabetes itself can affect nerves, and fatigue has many possible causes. That is why testing and clinical assessment matter. Tell your healthcare professional about new tingling rather than assuming it is simply part of diabetes. Early recognition is especially helpful when nerve symptoms are involved.
Who may benefit from a B12 discussion or test?
Talk about B12 if you have taken metformin for years, take a higher dose, or have symptoms or anaemia. Other reasons to bring it up include a vegan diet, limited animal-source foods, stomach or bowel conditions affecting absorption, previous gastrointestinal surgery or long-term use of acid-reducing medicine. A clinician may check a blood B12 level and sometimes use additional tests if the result and symptoms do not clearly agree.
There is no universal testing schedule that fits everyone. The question to ask at your next diabetes review is simple: “Given my metformin dose, how long I’ve taken it and my symptoms, should we check vitamin B12?” You can also ask when it should be reviewed again. The NICE guideline on B12 deficiency recognises metformin as a risk factor and provides a framework for diagnosis and treatment.
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If B12 is low, do you need tablets or injections?
That depends on the cause, symptoms and clinical findings. For B12 deficiency linked to a medicine, NICE says oral or injected replacement may be offered according to clinical judgment and the person’s preference. More significant neurological symptoms or a different cause of poor absorption may change the plan. Your clinician can also decide whether further evaluation is needed.
Foods such as fish, meat, eggs and dairy provide B12; fortified foods can help some people. Improving intake is worthwhile if your diet is low in B12, but food alone may not correct every established deficiency. Discuss the form and dose of replacement, as well as follow-up, instead of assuming one supplement suits all cases. A very high B12 label does not automatically make a product the best choice for you.
If you have not yet been tested, tell your clinician before starting a high-dose B12 product. NICE advises taking diagnostic blood samples before replacement because supplements can change the test result; significant symptoms may call for treatment without waiting for the result. If you already take a B12 product, share its label and dose with the testing team.
Product example, if your clinician recommends an oral B12 supplement: Supplify Vitamin B12 Drops at Body Attack is a B12-only option. Check the current label, dose and delivery availability for your country. Affiliate disclosure: WellNest Central may earn a commission if you buy through this link, at no extra cost to you. This product link is a shopping option, not a diagnosis or a substitute for the treatment plan your clinician recommends.
Three useful questions for your next appointment
- Could my symptoms be related to B12, blood sugar control, another condition or more than one cause?
- Should we test my B12 now, and what would we do if the result is borderline?
- If replacement is needed, which form and follow-up plan make sense for me while I continue metformin?
Keep a list of your medicines and supplements so the team can see the full picture. Our A1C guide explains a separate measure of longer-term blood sugar; a good A1C does not answer a question about vitamin B12 status. For a broader look at food sources, tests and supplements, read Vitamin B12 After 40.
The takeaway
Metformin and vitamin B12 deserve a place in the same conversation when symptoms or risk factors appear. Ask about testing, keep taking prescribed metformin unless your clinician advises otherwise, and use a tailored plan if deficiency is found. For help preparing questions about your health results and habits, reach WellNest Central.
This article is for general health education and does not replace individual medical advice, diagnosis, treatment or emergency care.
