Humulin R is a human insulin solution used to control blood sugar levels in people with diabetes mellitus. It works by replacing the insulin that is normally produced by the body to help regulate glucose (sugar) in the blood. This vial is typically administered through an injection and can be used alone or in combination with other insulin products. It is fast-acting, starting to work within 30 minutes, peaking in 2 to 4 hours, and lasting up to 8 hours. Alongside a healthy diet and regular exercise to effectively control blood sugar levels in diabetic patients.