Unfortunately diarrhoea is a common side effect of metformin therapy. Any patient with T2DM who develops diarrhoea should have the metformin stopped and then cautiously reintroduced once the diarrhoea has resolved at a lower dose. If the diarrhoea recurrs then the dose of metformin can be reduced to the highest tolerable dose that doesn't cause diarrhoea or the patient can be tried with the slow release formulation, Metformin M/R (TM). This generally has much better GI tolerability but does have a higher acquisition cost.

Diarrhoea can also be a symptom of autonomic neuropathy, where it is caused by small bowel bacterial overgrowth. The physician should be particularly alert to this possibility in those with long standing diabetes and with other neuropathic features.

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