Hi, Thanks for posting in HCM. I understand your concern. Plan B is an emergency contraceptive pill. It needs to be taken within 72 hours of unprotected intercourse. Earlier it is taken, the protection seems to be better. The pill would prevent pregnancy by causing withdrawal bleeding in the form of periods within 3 weeks from the day of its intake. Hence, accordingly your regular period dates could get altered. You might experience certain symptoms like abdominal discomfort, bloating, vaginal discharge or spotting as certain side effects, but these symptoms are known to eventually subside. In case you do not experience bleeding by 3 weeks, you need to take urine pregnancy test and seek medical attention promptly. The failure rate of using such pills is about 10%. Hope the information provided would be helpful. All the best.