Metformin is used in conjunction with diet and exercise to improve blood sugar control in adults with type 2 diabetes mellitus. Metformin is sometimes used together with insulin or other medications, but metformin is not used to treat type 1 diabetes. The recommended adult dosage generally start with 500 mg or 850 mg of Metformin or three times a day. The maximum daily dose is 3000 mg divided into 3 doses. If you have reduced kidney function, your doctor may prescribe a lower dose.