What is Levemir? Levemir (insulin detemir) is a man-made form of insulin, a hormone that is produced in the body. Insulin works by lowering levels of glucose (sugar) in the blood. Insulin detemir is a long-acting insulin that starts to work several hours after injection and keeps working evenly for 24 hours. Levemir is used to improve blood sugar control in adults and children with diabetes mellitus.