One tablet should be taken as soon as possible preferably within 12 hours, and no later than 72 hours after having unprotected sex. If vomiting occurs within three hours of taking the tablet, another tablet should be taken immediately. After using emergency contraception it is recommended to use a local barrier method (e.g. condom, diaphragm, spermicide, cervical cap) until the next menstrual period starts. The use of levonorgestrel does not contraindicate the continuation of regular hormonal contraception. Please note that Levonorgestrel does not work if you are already pregnant and does not stop a pregnancy.
Additionally, it is also important to note that an emergency contraceptive pill is less effective than other birth control methods (e.g. daily birth control pills) and therefore is intended to be used in emergency situations such as unexpected sex without contraceptive use, a broken condom, or rape. Furthermore, emergency contraceptives do not protect against STIs or HIV/AIDS.