Postinor 2, an emergency contraceptive pill containing levonorgestrel, generally stays active in the body for about 48 to 72 hours after taking it. Its effectiveness decreases significantly if taken beyond 72 hours after unprotected intercourse. The hormone reaches peak levels within around 2 hours of ingestion, with a half-life of about 26 hours, meaning the drug's concentration reduces by half every 26 hours. Side effects and hormone effects on the menstrual cycle can continue for a few days to a week, but the main contraceptive effect lasts mainly in those first 2 to 3 days after taking it. After about 5 days, the hormone's plasma concentration falls to negligible levels, and the pill is no longer effective. This corresponds roughly to the time sperm can survive in the female reproductive tract as well.
