Metformin and vitamin B12: when to ask about testing

What the medicines regulator says

The MHRA advises that metformin can lower vitamin B12 levels. The likelihood increases with longer treatment, higher doses and other risk factors. It recommends testing when deficiency is suspected and considering periodic monitoring for people with risk factors.

This is a reason for an individual conversation, rather than a recommendation that everyone taking metformin should buy a private vitamin panel. Ask the clinician managing your treatment whether a B12 test is appropriate and whether a recent result is already available.

Symptoms deserve a conversation

The MHRA advises seeking medical advice for new or worsening extreme tiredness, a sore red tongue, pins and needles, or pale or yellow skin while taking metformin. These symptoms can have other causes, so a blood result and clinical assessment may be needed. Do not assume that a supplement will resolve an unexplained symptom.

Make a note of what you have noticed and when it began. If symptoms are worsening, arrange advice rather than waiting for a routine paid review. Bring information about supplements you already take so your clinician has a complete account.

Prepare questions rather than self-diagnosing

A useful preparation sheet has three parts: your medicines list, your concerns and the follow-up already arranged. Include how long you have taken metformin if you know, its current strength and instructions, and any recent changes. If you have a B12 result, keep its date, units and laboratory range with it.

You do not need to decide whether you are deficient before asking for help. The aim of preparation is to make it easier for the clinician to assess the question and explain the next step.

• Do my symptoms or risk factors mean a B12 test would be useful?
• Have I already had this test, and what follow-up was agreed?
• Do any other medicines or supplements matter to this assessment?
• Who will explain the result and arrange treatment if it is needed?
• When should I get back in touch if the symptoms continue?

Keep your diabetes treatment plan in place

The MHRA advises patients not to stop metformin without discussing it with their doctor. Your clinician can explain how any investigation or treatment for low B12 fits alongside your existing diabetes care.

MedReview can help organise questions about your medicines and monitoring from the information you supply. It does not diagnose vitamin deficiency, provide a blood-test service or prescribe treatment. Use your usual clinician for assessment and follow-up; a private medicines report can support that conversation rather than replace it.