The morning after pill can reduce the risk of pregnancy up to 120 hours after unprotected vaginal intercourse. They work best when taken within 72 hours. Taken during this time they can reduce the risk of pregnancy from 75 to 89 percent. There are different methods. Please look at ec.princeton.edu/index.html for information. This website is available in Spanish, French, Arabic and English.

The pill does not protect against sexually transmitted diseases. It is not as effective as any ongoing contraceptive method, so a woman should never use it as only protection against pregnancy.
In some countries the emergency pill can be purchased at pharmacies or the chemist's, however in most countries they can only be bought on prescription.
To find out how you can use different normal contraceptive pills from around the world as the morning after pill (emergency contraception) click here http://ec.princeton.edu/worldwide/default.asp#country