A new review has found that the hormonal pill mifepristone is the most effective emergency contraception method to prevent unwanted pregnancy. In the United States, however, the drug has not gained government approval for this use.

With emergency contraception, women use hormonal pills or a copper intrauterine device to prevent pregnancy after unprotected intercourse. These methods are used after sex but before pregnancy occurs.

Most recommend use of the hormonal methods within 72 hours of unprotected sex. A clinician can insert a copper IUD up to five days after the estimated time of ovulation.

The aim of the systematic review was to determine which of several available emergency contraception methods is most effective in preventing pregnancy after unprotected sex.

The review appears in the current issue of The Cochrane Library, a publication of The Cochrane Collaboration, an international organization that evaluates research in all aspects of health care. Systematic reviews draw evidence-based conclusions about medical practice after considering both the content and quality of existing trials on a topic.

“Unwanted pregnancy is a common problem,” writes lead reviewer Linan Cheng, M.D. “Worldwide, about 50 million pregnancies are terminated each year.”

Cheng added that despite the number of terminated pregnancies, “except for a few Western European countries and China, emergency contraception is largely under-utilized worldwide.”

Cheng is director of the Shanghai Institute of Family Planning Technical Instruction in China.

She and her colleagues evaluated 81 clinical trials, 70 of which occurred in China. The review comprised 45,842 women who sought emergency contraception after one act of unprotected intercourse.

The clinical trials compared the effectiveness of the hormonal pills mifepristone and levonorgestrel, the Yuzpe regimen (a method of combination use of estrogen and progestogen repeated once 12 hours apart) and the copper IUD.

Most of the clinical trials studied mifepristone in two different doses — low dose (less than 25 milligrams) and middle dose (25 to 50 milligrams) and compared levonorgestrel in either a single dose of 1.5 milligrams or two (split) doses of 0.75 milligrams given 12 hours apart.

The Cochrane reviewers found mifepristone, given in the middle dose, was “superior to other hormonal regimens” in preventing pregnancy.

More pregnancies occurred with levonorgestrel than with either mid-dose mifepristone or low-dose mifepristone. Single-dose levonorgestrel had the same effectiveness as the split dose. Levonorgestrel, however, was more effective than the Yuzpe regimen in preventing pregnancy.

The Cochrane reviewers concluded that mifepristone “should be the first choice of hormonal emergency contraception” where available. If it is not available, “single-dose levonorgestrel 1.5 mg should be offered.”

However, mifepristone is not available as a method of emergency contraception in the United States. Experts explained that its current use — combined with another medication — for medical abortion has prohibited its acceptance.

“The problem with mifepristone is that it came down the market as the “abortion pill,” said Beth Jordan, M.D., medical director at the Association of Reproductive Health Professionals. “It’s the most politicized drug that we’ve ever encountered. Honestly, because it is so cheap and effective, it’s sad that it won’t get widespread use in the U.S. as an emergency contraception.”

The U.S. Food and Drug Administration (FDA) approved the split dose of levonorgestrel pills as the emergency contraception “Plan B.” Plan B became available over the counter to consumers 18 years and older in August 2006.

“Sales are going up, which is good,” Jordan said. “I think there’s a long road to go, however. Many more women need to be educated about the availability of emergency contraception. Women need to be taking it more often than they do.”

The Cochrane review disclosed that four co-authors are employees of the World Health Organization, which has a memorandum of understanding on the use of levonorgestrel with a company marketing the drug.

The Cochrane Collaboration is an international nonprofit, independent organization that produces and disseminates systematic reviews of health care interventions and promotes the search for evidence in the form of clinical trials and other studies of interventions.

Cheng L, et al. Interventions for emergency contraception. Cochrane Database of Systematic Reviews 2008, Issue 2.

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Source: Health Behavior News Service