Levonelle contains levonorgestrel, a synthetic version of the progesterone hormone. Levonelle primarily works by preventing the release of an egg (ovulation). However, it also increases the thickness of the mucus around the cervix. This can help by creating a barrier, that makes it difficult for sperm to pass through.
Levonelle is considered to be 95% effective 12 hours after unprotected sex. After 48 hours, the effectiveness of Levonelle is reduced to 58%. Other morning after pills, such as ellaOne can be effective up to 5 days after intercourse.