Some women may experience side effects including, changes in their period, such as a period that is heavier or lighter or a period that is early or late. If your period is more than a week late, you may be pregnant. Other side effects may include nausea, abdominal pain, tiredness, headache, dizziness, or breast tenderness. If you have severe abdominal pain, you may have an ectopic pregnancy, and should get immediate medical attention. If you vomit within 2 hours of taking the medication, call a healthcare professional to find out if you should repeat the dose.