Plan B is a drug (Levonorgestrel) designed to prevent pregnancy. It’s a form of emergency contraception that is most effective when taken within 72 hours of unprotected sex. The abortion pill is two separate drugs (mifepristone and misoprostol) designed to terminate an existing pregnancy. The first drug is often taken at the doctor’s office where prescribed, followed by the second drug at home at least 24 hours later. It causes cramping and sometimes heavy bleeding to end and then pass the pregnancy.