Metformin extended release (ER) (Glumetza, Depomed, Inc.) is a recently approved formulation that provides effective and well-tolerated glycaemic control with once-daily dosing. Metformin ER has similar bioavailability to conventional immediate-release (IR) formulations. In controlled clinical trials, metformin ER provided effective glycaemic control for 24 weeks when administered either as monotherapy or in combination with sulfonylurea. Good glycaemic control was maintained for an additional 24 weeks during an open-label extension study. Once-daily dosing with metformin ER 1500 mg/day was as effective as twice-daily dosing with metformin IR at the same total daily dose. Metformin ER was well tolerated at doses of 1500 or 2000 mg/day, with no increase in the frequency or severity of adverse events at the higher dose.