Plan B® (levonorgestrel) is emergency contraception. Emergency contraception is a backup method of preventing pregnancy and is not for routine use. Drugs used for emergency contraception are called emergency contraceptive pills, postcoital pills, or morning after pills.lan B® (levonorgestrel) works better the sooner you take it. Take the first Plan B® (levonorgestrel) tablet as soon as possible but not later than 3 days (72 hours) after unprotected sex. Take the second tablet 12 hours later.