Insulin is a hormone that works by lowering levels of glucose (sugar) in the blood. Insulin isophane is a intermediate-acting insulin. Insulin regular is an short-acting insulin. This combination insulin starts to work within 10 to 20 minutes after injection, peaks in 2 hours, and keeps working for up to 24 hours. Insulin isophane and insulin regular is a combination medicine used to improve blood sugar control in adults with diabetes mellitus. Insulin isophane and insulin regular may also be used for purposes not listed in this medication guide.