Metformin is a biguanide agent and the drug-of-choice for the treatment of newly diagnosed type-2 diabetes mellitus, making it one of the most widely prescribed medications in the world. With over half a century of clinical experience, metformin is generally recognized as safe with the most frequent adverse effects being gastrointestinal (i.e. nausea, indigestion, abdominal cramps/bloating, diarrhea). Metformin acts to reduce hepatic glucose production, reduce intestinal glucose absorption, and increase skeletal muscle glucose uptake and utilization. Because it does not affect the release of insulin or other pancreatic hormones, metformin is rarely associated with hypoglycemia.