Nortrel is a very effective form of birth control, with an effectiveness rate of almost 100% if taken correctly.[popover id=ref5] But the effectiveness rate drops slightly if you forget to take a pill or more during your cycle, or if the interval between pills exceeds 24 hours regularly. To be on the safe side, you should set an alarm on your phone to ring at the same time every day, and always have your pills with you in case you need to take one and you’re not at home.