Insulin is a hormone that works by lowering levels of glucose (sugar) in the blood. Insulin isophane is an intermediate-acting insulin that starts to work within 2 to 4 hours after injection, peaks in 4 to 12 hours, and keeps working for 12 to 18 hours. Insulin isophane is used to improve blood sugar control in adults and children with diabetes mellitus. Insulin isophane may also be used for purposes not listed in this medication guide.