Levonorgestrel is a hormonal medication which is used in a number of birth control methods. It is combined with an estrogen to make combination birth control pills. As an emergency birth control, sold under the brand name Plan B One-Step among others, it is useful within 72 hours of unprotected sex.
The morning-after pill is super safe, and Plan B side effects aren’t super common. There have been no reports of serious problems out of the millions of people who’ve taken it. After you take the morning-after pill, it’s totally normal for your next period to be different from what you’re used to.