The morning-after pill may be safe and effective as a regular birth control method, researchers say.
In the U.S., the pill costs between $10 and $70 and is available over the counter for people over 17. However, it is only approved as an emergency backup after unprotected sex, and the government discourages using it as regular contraception.
The new report, published in the journal Obstetrics and Gynecology, is based on a review of earlier studies of levonorgestrel, a synthetic hormone used in most morning-after pills (brands include Plan B One-Step and Next Choice).
Researchers found the morning-after pill compared favorably with condoms and spermicides in terms of reported rates of unwanted pregnancies. The studies didn't compare different birth control methods directly, though.
Women who used the pill around the time they had sex had an estimated 5-percent chance of getting pregnant over one year, compared to 16 percent among women whose partner used a condom.
However, taking a morning-after pill at the time of intercourse is not as effective as methods women use on a longer basis, such as patches or regular birth control pills, said Dr. Deborah Nucatola of Planned Parenthood of America, who was not involved in the study.
Even so, there are reasons a woman might want to use the morning-after pill just before or after sex instead of taking birth control all the time, she told Reuters Health -- for instance, if she doesn't have sex frequently.
Out of a total of about 8400 women in the 15 studies the researchers reviewed, there were 267 pregnancies.
In most studies, women took only half as much levonorgestrel as is in the morning after pill, meant for a one-time emergency use. The most common side effect was irregular bleeding, affecting about two to nine out of ten women.
Most women didn't see this as a reason to stop using the hormone, Nucatola said. "Almost 70 percent of women thought this was acceptable, even with changes in their bleeding," she said.
Levonorgestrel works by stopping ovulation, and it's also found in some traditional birth control pills. According to the new study, it's used by some women in Africa and Asia as a planned method of birth control, instead of an emergency backup.
However, the researchers don't know how many women this is, or how many would want to use levonorgestrel in this way.
"How many women would want this if this method were actually available, that would be very nice to know," said study author Dr. Elizabeth Raymond of Gynuity Health Projects in New York.
Raymond has been a paid consultant or received funding from Watson Pharmaceutical, Teva Pharmaceutical, and HRA Pharma, which all make birth control pills containing levonorgestrel.
Nucatola said the new findings were promising, "but we need better long-term studies."