Morning-after pills are not the same as the so-called “abortion pill,” known as mifepristone (commercially, Mifeprex) or RU-486. That drug will terminate pregnancy when the fertilized egg has attached to the uterine wall and has begun growing.

The morning-after pill is not fool-proof and may not prevent pregnancy, which is why it is not recommended for routine contraceptive use. Even if used correctly, it can fail, and it offers no protection against sexually transmitted diseases.

Doctors recommend that patients not take the morning-after pill if they are allergic to any of its components; if taking St. John’s wort, barbiturates or other medications that may interfere with its efficacy; or if already pregnant. Those who are overweight may not be as susceptible to the pill’s effects on the body as it is for normal-weight women.

Ulipristal use requires that a woman is not pregnant or breastfeeding because it can affect the unborn fetus in ways that aren’t entirely clear. Taking levonorgestrel if already pregnant will have no effect.

Side Effects of Emergency Contraception

The morning-after pill has effects beyond pregnancy. Ingesting it can cause vomiting or nausea, fatigue, breast tenderness, headache, bleeding between periods or heavier than usual menstrual flow, and abdominal cramps or pain.

If vomiting commences within two hours of taking the morning-after pill, it may be necessary to consult a doctor. The medical professional will advise whether another dose is necessary to achieve protection.