Hello dear, Thank you for your question. I carefully read your question. Emergency contraception is widely accepted to be a safe and effective way to prevent unwanted pregnancies. The active principle of postinor2 is called levonorgestrel. This drug is 95% successful in preventing a pregnancy if it is taken within 24 hours of unprotected sexual intercourse. Considering you took the pill around your ovulation day, I would expect that your periods will have a delay. It usually would be around a week later than you might expect. Levonorgestrel is basically a hormone that you take as a pill and therefore is expected to temporarily change the biology of your reproductive system. You may experience: irregular bleeding, nausea, vomiting, abdominal pain or bloating, tenderness of the breasts etc. These side effect are usually minor and tend to fade away in a couple of days. If your delay lasts more than a week ,then it is highly unlikely that pill is the cause of this delay and you need to take a pregnancy test. I hope this helped. Don t hesitate to contact me if you have further questions. All the best, Dr. Alma