How long after sex can you take the Plan B pill for it to be effective?

Within 72 hours. It is recommended that you take it as soon as possible and can be effective if taken within 72 hours (3 days). Just remember, the pill only prevents pregnancy and not stds...So, be wise and protect yourself. Good luck.
Up to 72 hours. It is recommended the pill be taken as soon as possible and can be effective as long as it is used within 72 hours after unprotected relation. Just remember, the pill only helps prevent pregnancy and not std. Good luck.