Digestive disorders (diarrhoea, vomiting) represent the most common metformin side-effects (around 30%) with this first-line drug treatment for type 2 diabetes. In healthy individuals, metformin affects glucose, vitamin B12 and the digestive uptake of bile salts. In the colon, it acts locally by modifying glucose cell metabolism. Different pathophysiological hypotheses have been proposed to explain the metformin-induced diarrhoea and vomiting, which can sometimes cause the patient to stop an effective treatment. These theories include stimulation of intestinal secretion of serotonin, changes in incretin and glucose metabolism, and bile-salt malabsorption. However, none of these hypotheses can be considered an adequate pathophysiological explanation of metformin digestive side-effects. In addition, there is a lack of experimental data to explain these highly patient-dependent adverse effects.
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