Plan B (levonorgestrel) typically stays in your system for about 5 to 6 days after you take it, though its active hormone levels decrease significantly within the first 1 to 2 days. The half-life of levonorgestrel is approximately 27 hours, meaning it takes that long for half of the drug to be eliminated from your body

. Plan B is most effective when taken as soon as possible after unprotected sex, ideally within 72 hours (3 days), but it can reduce the risk of pregnancy if taken up to 5 days (120 hours) afterwards, though with decreasing effectiveness over time

. The medication is eliminated primarily through urine and feces, with small amounts potentially remaining detectable for up to 5 days

. After this period, the hormone concentration falls to negligible levels and the pill no longer provides contraceptive protection

. In summary:

• Plan B's hormone (levonorgestrel) has a half-life of about 27 hours.
• It remains active and effective for about 3 to 5 days after ingestion.
• The drug is mostly cleared from the body within 5 to 6 days.
• Effectiveness is highest when taken within 24 hours and decreases thereafter.

This timeline explains why Plan B is recommended for emergency contraception use shortly after unprotected sex and not as a regular contraceptive method