Metarin 850 mg is an oral medication containing metformin hydrochloride, a biguanide-class antihyperglycemic agent. It is primarily used in the management of type 2 diabetes mellitus, particularly in overweight patients when dietary management and exercise alone do not result in adequate glycemic control. Metformin works by decreasing hepatic glucose production, decreasing intestinal absorption of glucose, and improving insulin sensitivity by increasing peripheral glucose uptake and utilization. This combination helps in controlling blood sugar levels without causing hypoglycemia.