After determining whether EC is indicated, explain the method to the adolescent and the possibility of failure of the method. Explain that the next period might be early, on time or late. Discuss her options should she become pregnant (see statement on “Adolescent pregnancy”  ). Explain that if she is going to have sexual intercourse before her next period, she should use a barrier method with a spermicide; she may be at risk for pregnancy in the first few days after completing EC treatment because one of the primary ways that EC works is by delaying ovulation. If the patient is taking EC because she has missed birth control pills, or because she wants to start to take the pill and has no contraindications, she can start a new pack of pills the day after she takes EC. She should be told that ECs do not prevent or treat STIs.
Over time, interest in progestin-only treatments increased. The Special Program on Human Reproduction (HRP), an international organization whose members include the World Bank and World Health Organization , "played a pioneering role in emergency contraception" by "confirming the effectiveness of levonorgestrel."  After the WHO conducted a large trial comparing Yuzpe and levonorgestrel in 1998,   combined estrogen-progestin products were gradually withdrawn from some markets ( Preven in the United States discontinued May 2004, Schering PC4 in the UK discontinued October 2001, and Tetragynon in France) in favor of progestin-only EC, although prescription-only dedicated Yuzpe regimen products are still available in some countries.