Metformin-Induced Chronic Diarrhea Misdiagnosed as Irritable Bowel Syndrome for Years.

Metformin is the most prescribed and recommended drug for type 2 diabetes mellitus because of its better tolerability, pleiotropic benefits, and cost-effectiveness. Metformin inhibits hepatic glucose production and increases muscle glucose uptake. Metformin is also associated with gastrointestinal side effects like abdominal bloating, flatulence, diarrhea, nausea, and vomiting. Metformin-related gastrointestinal side effects are mainly due to alteration in gut microbiota, raised intestinal glucose, and increased ileal bile salt reabsorption. We report a case of a 62-year-old diabetic patient who presented with chronic diarrhea with a weight loss of 6 kg from the last six years after initiation of metformin. He underwent multiple investigations and was finally misdiagnosed with irritable bowel syndrome for years. After discontinuation of metformin, there was a significant improvement in gastrointestinal symptoms. Our case highlights the importance of metformin-induced chronic diarrhea if no other causes for the diarrhea are obvious in patients with type 2 diabetes taking metformin. Consideration of this potential side effect of metformin must be valuable to avoid unwarranted investigations, additional drug therapy, and annoyance of the patients.