Humulin N, an intermediate-acting insulin, has an onset of one to three hours, peak of eight hours and duration of 12 to 16 hours. Humulin R, a short-acting insulin, has an onset of 30 to 60 minutes, a peak of two to four hours, and a duration of five to eight hours.
An insulin's onset indicates when the it begins to lower blood glucose, and the peak is the time the insulin is working hardest to decrease blood glucose. The duration describes how long the insulin lasts. Because Humulin R has a faster onset, it is usually injected 30 minutes before meals. If a patient does not eat soon after taking Humulin R, low blood sugar levels may result. In contrast, it is not imperative to eat directly after taking Humulin N, which is usually injected one or two times a day.
Both Humulin N and Humulin R are synthetic insulin products that are the same as human insulin. Insulin works by helping blood glucose enter cells and be utilized for energy. Humulin N and Humulin R are sometimes used together to achieve blood glucose control. They are given as an injection under the skin in the stomach, thighs, buttocks or the back of the upper arm.