Hi there and thanks for sharing your concern with us at HCM. Postinor 2 can prevent 95% of pregnancies if taken with 24 hours of unprotected sex, 85% effective if taken between 25 to 48 hours and 58% effective if taken within 49 to 72 hours of unprotected sex. It is unknown if it can prevent pregnancies if taken after 72 hours of unprotected sex. Postinor 2 is an EMERGENCY contraceptive - you should not use it regularly for contraception as it will confuse your body and potentially cause hormonal imbalance which can lead to erratic menstrual cycles. Some women have earlier periods while others may even miss a cycle after taking postinor. There is still a real risk that you might have fallen pregnant. You could perform a home pregnancy test (not very accurate). I d recommend you wait 3 days at least. If you still don t get your period, do visit your regular doctor and get them to do a blood test for serum beta HCG - this is the most accurate way to determine if you are pregnant or not. Hope this helps. Thank you Dr Shabnam