Metformin, a member of the biguanide class of antidiabetic drugs, primarily works by inhibiting gluconeogenesis and glycogenolysis, thereby reducing glucose output from the liver and lowering blood sugar levels. It also enhances glucose transport in peripheral tissues, promoting glucose uptake and utilization, while aiding in weight reduction, improving insulin sensitivity, and alleviating insulin resistance. Biguanides are contraindicated in patients with diabetic ketoacidosis, acute infections, congestive heart failure, hepatic or renal insufficiency, or any condition involving hypoxia. They are generally not recommended for children unless there is a confirmed diagnosis of obesity-related type 2 diabetes and definite insulin resistance. Pregnant and breastfeeding women should also avoid using these medications. Elderly patients should use them with caution, with dosage adjustments and regular monitoring of renal function.