When contraception fails …
Most teenagers do not know about the availability of emergency contraception to be taken 48-72 hours after unprotected sex (which may be consensual, forced or unexpected intercourse resulting from rape or coercion or when the person knows that the method of contraception is likely to have failed).
It can cause unpleasant side effects; most common are nausea and vomiting. If she vomits within 2 hours of taking the pill, she should repeat the dose as soon as possible.
Other side effects are: abdominal (stomach) pain, fatigue, headache, dizziness and breast tenderness. The side effects should resolve within 24 hours.