Hi Thanks for contactingHCM My self Dr Abhishek Effectiveness of morning contraceptive pills are more effective if it is taken as soon as possible after unprotected method . People sometimes call it the morning after pill. But you don t have to wait until the morning after sex to take it. In fact, Plan B is more effective the sooner you take it. It is a one-dose regimen: you take one pill. The pill contains 1.5 milligrams of levonorgestrel, which is used in lower doses in many birth control pills. It works depending upon where you are in your cycle, Plan B One-Step may work in one of these ways: It may prevent or delay ovulation. It may interfere with fertilization of an egg. It is also possible that this type of emergency birth control prevents implantation of a fertilized egg in the uterus by altering its lining. If you take it within 72 hours after you ve had unprotected sex, Plan B One-Step can reduce the risk of pregnancy by up to 89%. If you take Plan B One-Step within 24 hours, it is about 95% effective. But you should know that Plan B One-Step is not as effective as regular contraception. Potential side effects are include: nausea abdominal pain fatigue headache menstrual changes dizziness breast tenderness vomiting If you vomit within two hours after taking the drug, call a healthcare professional to find out if you should repeat the dose.