Effectiveness of emergency contraceptive pills

Dear Ask The Doctor: My bf had sex with me 3-4 days after my last period, and i took postinor 2 ,2 hours after sex , will i be pregnant ??

Dear Adeline: An emergency contraceptive pill  works by preventing ovulation and/or thickening the cervical mucous and thus helps in preventing pregnancy. Typically it should be taken immediately to upto 72 hours after unprotected intercourse. The earlier the better. Though no birth control measure is 100% effective, emergency contraceptive are around 90% effective in reducing the chances of pregnancy if taken within 24 hours of sex.