Emergency Contraception: A Cost-Effective Approach to Preventing Unintended Pregnancy

James Trussell, PhD, Charlotte Ellertson, PhD, Felicia Stewart, MD, Jacqueline Koenig, MSB, Elizabeth G. Raymond, MD, MPH, and Tara Shochet, MPH


April 27, 2000

In This Article

Combined Emergency Contraceptives

Combined ECPs are ordinary birth control pills containing the hormones estrogen and progestin. Although this therapy is commonly known as the morning-after pill, the term is misleading; ECPs may be initiated sooner than the morning after (immediately after unprotected intercourse) or later (for at least 72 hours after unprotected intercourse). The only hormones that have been studied in clinical trials of ECPs are the estrogen ethinyl estradiol and the progestin levonorgestrel or norgestrel (which contains 2 isomers, only 1 of which -- levonorgestrel -- is bioactive). These are found in 12 brands of combined oral contraceptives available in the United States as well as in 1 dedicated ECP product (Table).[7]

Use of combined ECPs reduces the risk of pregnancy by about 75%.[8,9,10] This statement does not mean that 25% of women using ECPs will become pregnant. Rather, if 100 women had unprotected intercourse once during the second or third week of their cycle, about 8 would become pregnant; following treatment with ECPs, only 2 would become pregnant -- a 75% reduction. The current treatment schedule is 1 dose within 72 hours after unprotected intercourse, and a second dose 12 hours after the first dose. A recent large study by the World Health Organization found that effectiveness declined significantly with increasing delay between unprotected intercourse and the initiation of treatment.[11,12] This finding suggests that ECPs should be taken as soon after unprotected intercourse as is practical. In cases where it would be difficult to take the second dose 12 hours later, the timing of the second dose might be altered; for example, a woman who took her first dose at 3 PM immediately following discovery of a burst condom might delay taking the second dose until 7 AM. The goal should be to make the therapy as user-friendly as possible.[13]

It is biologically implausible that efficacy would abruptly plummet to zero after 72 hours.[14] Therefore, clinical protocols that deny treatment beyond 72 hours seem excessively restrictive, particularly if the alternative of emergency insertion of a copper-T IUD is not immediately available or appropriate.

About 50% of women who take combined ECPs experience nausea, and 20% vomit.[8,11] If vomiting occurs within 2 hours after taking a dose, some clinicians recommend repeating that dose. The results of one study suggest that ECPs containing levonorgestrel have an incidence of side effects substantially lower than do ECPs containing norgestrel[15] (see note c to Table for information on progestins in ECPs). The nonprescription antinausea medicine meclizine has been demonstrated to reduce the risk of nausea by 27% and vomiting by 64% when two 25-mg tablets are taken 1 hour before combined ECPs, but the risk of drowsiness was doubled (to about 30%).[16] Antinausea medicines are not routinely offered in the United States. Instead, many providers of ECPs recommend that women take them with food to reduce the risk of nausea, although research suggests that doing so is ineffective.[16]

Almost all women can safely use combined ECPs. The only absolute contraindication to use of combined ECPs is confirmed pregnancy, simply because ECPs will not work if a woman is pregnant. Treatment may not be appropriate for those who have an active migraine with marked neurologic symptoms or crescendo migraine.[17] Given the very short duration of exposure and low total hormone content, combined ECP treatment can be considered safe for women who would ordinarily be cautioned against use of combined oral contraceptives for ongoing contraception. Although no changes in clotting factors have been detected following combined ECP treatment,[18] progestin-only ECPs or insertion of a copper IUD may be preferable to use of combined ECPs for a woman who has a history of stroke or blood clots in the lungs or legs and wants emergency contraceptive treatment. All 3 of these conditions (pregnancy, migraine, and history of thromboembolism) are identified through medical history screening, so women requesting combined ECPs can be evaluated via telephone, without need for an office visit, pelvic exam, or laboratory tests. Planned Parenthood of America now allows affiliates to prescribe ECPs via telephone.

There have been no conclusive studies of births to women who were already pregnant when they took combined ECPs or following failure of combined ECPs. However, there are 2 observations that provide reassurance for any concern about birth defects.[5] First, in the event of treatment failure, ECPs are taken long before organogenesis starts so that they should not have a teratogenic effect. Second, studies that have examined births to women who inadvertently continued to take combined oral contraceptives without knowing they were pregnant have found no increased risk of birth defects.[19,20,21] The FDA removed warnings from the package insert several years ago about adverse effects of combined oral contraceptives on the fetus.[22]

Several clinical studies have shown that combined ECPs can inhibit or delay ovulation.[23,24,25] This is an important mechanism of action and may explain ECP effectiveness when used during the first half of the menstrual cycle, before ovulation has occurred. Some studies have shown histologic or biochemical alterations in the endometrium after treatment with the regimen, leading to the conclusion that combined ECPs may act by impairing endometrial receptivity to implantation of a fertilized egg.[24,26,27,28] However, other studies have found no such effects on the endometrium.[23,29] Additional possible mechanisms include interference with corpus luteum function; thickening of the cervical mucus, resulting in trapping of sperm; alterations in the tubal transport of sperm, egg, or embryo; and direct inhibition of fertilization.[5,30] No clinical data exist regarding the last 3 of these possibilities. Nevertheless, statistical evidence on the effectiveness of combined ECPs suggests that there must be a mechanism of action other than delaying or preventing ovulation.[31] ECPs do not interrupt an established pregnancy, defined by the National Institutes of Health/Food and Drug Administration[32] and the American College of Obstetricians and Gynecologists[33] as beginning with implantation. To make an informed choice, women must know that combined ECPs -- like all regular hormonal contraceptives, such as the birth control pill, the implant Norplant, and the injectable Depo-Provera,[34] and even breastfeeding[35] -- may prevent pregnancy by delaying or inhibiting ovulation, inhibiting fertilization, or inhibiting implantation of a fertilized egg.


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