Metformin adverse effectsprecautions, warnings, drug interactions, allergic reactions, or adverse effects. For your information, the following is a list of adverse effects that may be caused after administration of metformin: Metformin Side Effects: Diarrhea. Patients tolerate metformin and sulfonylurea drugs, the two first-line treatments of choice for type 2 diabetes, generally well. . Since Metformin affects the liver's production of glucose, it also can have adverse effects. . We could tal... more