Hello and Welcome to ‘Ask A Doctor’ service. I have reviewed your query and here is my advice. Postinor pil is a two tablet containing 1.5 mg of synthetic progestin, levonorgestrel. It is used in case of: 1. Unprotected intercourse 2. Unwanted conception 3. Sexual abuse, rape or incest For this emergency contraception to be effective, it is necessary to take one 1.5 mg pill of levonorgestrel on a single day and within 72 hours of unprotected intercourse. Best results are seen when Unwanted 72 is taken quickly, within 72 hours of an event, as it takes 72 hours after fertilization for a woman’s body to produce a pregnancy. The level of protection provided by Unwanted 72 is as follows: If taken - within 24 hours – up to 95% effective - within 24 to 48 hours – 85% effective - within 48 to 72 hours – 58% effective If a woman should vomit after taking Unwanted 72, it is recommended to repeat the one time dose for effectiveness in pregnancy prevention under the direction of a health care provider. So, it may be ineffective in 5%. Postinor causes late period due to hormonal imbalance. So, do not worry. It haapens. Hope I have answered your query. Let me know if I can assist you further. Regards, Dr. Dholariya Sagar Jayantilal