FCOG-0919

An 20-year-old woman presents to you 6 hours after she was raped on day-12 of her menses which usually lasts for 28 days. You have decided to give her Postinor-2 (levonorgestrel 0.75 mg) as a post-intercourse contraceptive. She is requesting information about any potential adverse effects as well as its efficacy.

Which of the following statements is correct?