Long-term metformin reduces vitamin B12 absorption, and deficiency becomes more likely with higher doses and longer use. Its effects — peripheral neuropathy, anaemia, cognitive change — are easily attributed to diabetes or ageing. Guidelines suggest checking B12 periodically in long-term metformin users, and particularly in anyone with neuropathy or anaemia. Treatment does not require stopping metformin.
- Check B12 in long-term users, and at once if neuropathy or anaemia appears
- Risk rises with dose and duration
- Replace B12 and continue metformin
- Vegetarian diets, common in India, add to the risk
Why it matters
It is a treatable drug harm that is routinely mistaken for the disease the drug is treating.
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