What are the different types of insulin and their onset times?

Insulin types are classified by speed of action. Rapid-acting insulins like lispro, aspart, and glulisine begin working within 15 minutes and peak in one to two hours, used for mealtime glucose control. Short-acting regular insulin begins in 30 minutes, peaks in two to four hours, and is the only insulin given intravenously. Intermediate-acting NPH insulin begins in one to two hours and peaks in four to twelve hours. Long-acting insulins like glargine and detemir begin in one to two hours with no pronounced peak and last 24 hours, providing basal coverage.