Researchers are stopping a study testing a daily pill to prevent infection with the AIDS virus in thousands of African women.
Partial results show that women taking Truvada, made by Gilead Sciences Inc., are just as likely to get HIV as other women who take dummy pills.
Even if the study continues, it will not be able to determine whether the pills do any good. The results are a disappointment because a study last fall found that Truvada did help prevent infections in gay and bisexual men, and many AIDS experts view it as a breakthrough.
The new study's results were announced on Monday.
In the earlier study on Truvada, researchers found that the drug cut new HIV infections by 44 percent among gay and bisexual men, reports WebMD.
The study of the effects of Truvada on men began in 2007 in Brazil, Ecuador, Peru, South Africa, Thailand, and the U.S.
The Wall Street Journal reports that Truvada had U.S. sales of $1.3 billion last year.