How many hours does it take for humulin (insulin) to work?

Depends. Humulin (insulin) n is a brand of Insulin nph w/onset in 1-2hrs, peak in 4-14hrs & duration of 10->24hrs. Humulin (insulin) r is a brand of Insulin regular w/onset 30min-1hr, peak in 2-4hrs & duration of 6-12hrs. If you're ever unsure, ask your doctor & pharmacist!