Insulin is a hormone that is produced in the body. It works by lowering levels of glucose (sugar) in the blood. Insulin aspart is a fast-acting form of insulin. Insulin aspart is used to treat type 1 (insulin-dependent) diabetes in adults and children who are at least 2 years old. Insulin aspart is usually given together with another long-acting insulin. Insulin aspart may also be used for other purposes not listed in this medication guide.