Hello, Welcome to HCM, I have read your query, as postinor contains levonorgestrel and can be taken as emergency contraceptive. It prevents the egg from meeting the sperm by making changes in uterine lining and mucus so as to prevent fertilization to occur. It prevents pregnancy before fertilization but if there is existing pregnancy it will not stop it. The most serious side effect of this drug is the change it brings out in the periodic cycle. The changes can range in severity from very little to very high. The most extreme is non- stop bleeding with a long time span cycle. The only reason behind the usage even with the knowledge of its side effects, is the efficiency it provides to stop fertilization which may result in pregnancy. But nowadays, there are many other ways like contraceptive pills, injective medicines to be utilized as a substitute of this method. These are proven to be much protective and nil from any side effects. If you have any of the above stated conditions progress, then will recommend you to visit your gynaecologist. Thanks