Morning After Pill

Teresa C. Menart, MD
Reproduced with permission

What is it?

The morning after pill (currently being marketed as the Preven emergency contraceptive kit) is simply a series of birth control pills that are used after an act of intercourse, rather than before. Usually 2 pills are taken within 72 hours of intercourse, and 2 more are taken 12 hours later. For several years these pills have been given to rape victims in emergency rooms. There is currently a significant marketing effort to make Preven widely available.

How does it work?

There are a few possibilities. The pills may delay ovulation or impair thetransportation of the sperm or egg, thus preventing conception. Since conception can occur anytime from a few hours toabout 2 days after intercourse, these mechanisms COULD come into play if the pills were taken soon enough after intercourse and during the right part of the woman's cycle. The other mechanism of action is for the pills to alter the lining of the uterus, making it very difficult for the embryo to implant if conception has occurred. If implantation were prevented, a new life would be destroyed . If conception (fertilization) has already taken place, this is the only mechanism by which the pills could be effective. With currently available technology there is no way for a woman to know, at the time she takes these pills, whether or not she has already conceived. A pregnancy test cannot give her this information. Therefore, there is always the risk that a new life will be destroyed.

Does this mean the morning after pill is an abortifacient -- a pill that causes abortion?

Life begins at conception, also called fertilization. The morning after pill can cause the death of a new human being. However, it is important to be aware of how the medical community is using these terms. Pregnancy has been defined as beginning at the time of implantation, and an abortifacient is something that interrupts a pregnancy. Since implantation occurs 5 to 7 days after conception, pills that destroy a new human being by preventing implantation would not be called "abortifacient" according to these new definitions.

How effective is the morning after pill?

This is difficult to evaluate because the woman may not be in the fertile phase of her cycle when she has intercourse. Most of the time she is not fertile and would not have conceived. It is generally held that the pills reduce the chance of pregnancy by about 75%.

Are there side effects?

The most common side effects are nausea, which occurs in up to 50% of women, and vomiting, which occurs in up to 25%. Other side effects include headache, breast soreness, fatigue, abdominal pain, and dizziness.

What can we expect in the future?

We can anticipate the marketing of additional "emergency contraceptive kits." 'Plan B' is a set of "morning after pills" containing only progesterone which may be next on the market. The progesterone-only pills have fewer side effects than the combination estrogen and progesterone pills (Ovral, Preven). We may also see mifeprostone (RU-486), the controversial abortion pill) marketed for this purpose. All these methods have the potential to prevent implantation, thus ending a life already begun.


1. The Medical Letter 40 (1038): 102-103, Oct. 23, 1998

2. Hatcher R.A., Contraceptive Technology Ardent Media, Inc. New York, NY 1994 and 1998

3. Glasier A., Emergency Postcoital Contraception, NEJM 337(15) 1058-1064; Oct 9, 1997