For many African women, the generic version of the hormonal birth-control drug Depo-Provera is a godsend. Just one injection every three months allows them to know with near-100-percent certainty that they will not conceive unexpectedly. In poverty-stricken nations where mothers frequently suffer serious health complications from childbirth, that assurance can literally be a lifesaver, which explains why roughly 12 million women across the continent currently get the injections.

But new research from the University of Washington suggests that the drug may also double the chances that women and their partners will contract HIV, a finding with alarming implications for global health officials battling Africa’s AIDS epidemic.

The research was published last week in a medical journal devoted to infectious diseases and went viral after it was picked up by The New York Times. Renee Heffron, co-author of the study, spoke to Seattle Weekly from Kenya via Skype. Now in her fourth and final year at UW’s graduate school of public health, Heffron, 32, says she has lived in Africa off and on for about six years. It was there that she first became interested in AIDS. “I developed an interest primarily in HIV,” she says. “The women are exposed often to HIV, but there are also questions about reproductive health and having children and families. It’s complicated.”

Heffron says she and UW’s Dr. Jared Baeten began to look at the use of hormonal contraceptives, the most popular of which is the generic version of Pfizer’s Depo-Provera. The drug works by elevating levels of the hormone progestogen, thereby tricking a woman’s body into thinking she is already pregnant.

The researchers tracked the sexual activity of 3,800 couples in Botswana, Kenya, Rwanda, South Africa, Tanzania, Uganda, and Zambia. In each couple, either the man or the woman was already infected with HIV. They followed most couples for two years, had them report their contraception methods, and noted whether the uninfected partner contracted HIV from his or her infected partner.

“We measured concentration of HIV in their genital fluids,” Heffron explains. “We saw that women using hormonal contraceptives—especially injectables—had a higher concentration of HIV than women not using any hormonal contraceptive. We also know that if you have a higher concentration of HIV in your [genital] swab, you’re more likely to transmit the virus.”

In their findings, the UW scientists concluded that women using hormonal contraception are nearly twice as likely to contract HIV as those not using that method. Their male partners also face an elevated risk of getting the virus. And the study has prompted the World Health Organization to schedule a meeting in January in Geneva to discuss whether it ought to advise women that hormonal contraceptives may increase their risk of getting or transmitting HIV.

Precisely why the hormones increase the odds of getting HIV remains unclear, Heffron says. As additional research is conducted, she suggests that women already receiving shots combine the treatment with condoms rather than switch to birth-control pills or an IUD. “Switching to another method is really tricky,” Heffron says. “There are other methods out there . . . but these methods just aren’t widely used. People can’t access or don’t like them. Until we know better how to make these user-friendly, the importance of condom use when using hormonal contraceptives can’t be stressed enough.”

Approximately 1.2 million American women also use some form of Depo-Provera. But whether they too should be concerned about HIV remains to be seen, says Heffron.

“We only studied African women,” she says. “We can’t make conclusions about women from other places. But there is no biological reason why we’d think they would be different.”