Hi Sometimes, emergency contraception can change the length of your monthly menstrual cycle, making your next period come as much as a week earlier or a week later than usual. Some women also find that the hormones in the pills can cause unexpected bleeding, but this is not a common or serious side effect.If the bleeding extends more than seven days,associated with clots or abdominal cramps,visiting your gynaecologist is essential as excess bleeding may cause anemia. Hope I have answered your query. Let me know if I can assist you further. Regards Dr.Saranya Ramadoss, General and Family Physician