The first formal testing of the abortion pill RU-486 in the United States found that it successfully ended pregnancies in 92 percent of women.
Although the drug has already been widely tested and used in Europe, the Food and Drug administration requested that additional studies of its safety and effectiveness be done in the United States.
Those results are being published in today's issue of the New England Journal of Medicine. The drug's U.S. developer says it hopes to have the pill on the market sometime next year.
In this study, the drug was slightly less effective than in earlier European experiments, where it triggered abortions in 96 percent to 99 percent of women.
Success meant that the women expelled their fetuses without the need for surgery. The approach was considered a failure if women did not abort after 15 days, although some abortions might have occurred after this.
The researchers said the pill may have appeared to work less well in this test because U.S. doctors are inexperienced at giving abortion medicines, or because of the way the study was designed.
The Population Council was given U.S. rights to the medicine in 1994 by the French manufacturer Roussel Uclaf. The FDA declared the drug safe and effective in 1996, after reviewing European data and early results from the U.S. study.
The Population Council licensed its rights to the drug to the Danco Group, a new pharmaceutical firm, after plans to get the drug made by a Hungarian company fell through.
At Danco, spokeswoman Heather O'Neill said the company has found a manufacturer, which she declined to identify, and is working out details with the FDA to get the drug on the market next year.
The study found the drug was most effective when given within 49 days of gestation. The longer a woman had been pregnant, the less likely the pill was to work. Among women who were pregnant between eight and nine weeks, it was 77 percent effective.