Metformin hydrochloride (Glucophagefreg], Bristol-Myers Squibb) is a biguanide oral antihy-perglycemic agent effective in treating non-insulin-dependent diabetes mellitus (NIDDM). Although metformin may be added to regimens containing sulfonylureas, it is also highly effective as initial monotherapy in patients with newly diagnosed NIDDM.Metformin reduces hepatic glucose production by decreasing gluconeogenesis, thus reducing hyperglycemia and improving glucose tolerance. It enhances insulin-stimulated glucose utilization in peripheral tissues, particularly skeletal muscle, as well as fat and intestinal tissue, without stimulating insulin secretion.Metformin is superior in efficacy to placebo and comparable in efficacy to the sulfonylureas. However, metformin does not induce hypoglycemia or body weight gain in lean or overweight patients. Metformin reduces insulinemia and has favorable effects on plasma lipid profiles, possibly diastolic blood pressure, and other established cardiovascular disease risk factors.Metformin is well tolerated, with most adverse events being gastrointestinal and transient in nature. Lactic acidosis, a significant risk with phenformin therapy, occurs very rarely with metformin. Thus, metformin is an effective and well-tolerated initial treatment for NIDDM. In addition to having beneficial effects on glycemia and insulinemia, metformin, compared to other antidiabetic therapies, nas a I positive influence on lipid profiles and body weight.