For the last year, Brandi Cooper has taken a once-a-day pill to help protect herself from HIV. It's simple and proven effective, and the Philadelphia woman has enthusiastically shared her find with perhaps 10 other women. Most had never heard of it; only one has taken her suggestion.

That, in a nutshell, is the problem facing PrEP for women.

"This message is just not getting out," said family nurse practitioner Anne M. Teitelman, who is launching a study to try to determine why – and what can be done about it. "There is a life-saving medication available, and women don't know about it. That seems important."

It is particularly important in Philadelphia, where the simple fact of being female and African American, as Cooper is, significantly increases the risk of contracting HIV.

PrEP stands for Pre-Exposure Prophylaxis. The Food and Drug Administration approved Truvada  in 2012 to lower the odds of infection for HIV-negative people who are at high risk. The blue caplet did not catch on immediately. When it did, the exciting news traveled almost entirely by word of mouth and social media shared by gay men, who are at the highest risk of contracting HIV.

Between the first quarter of 2013 and the first quarter of 2016, prescriptions rose just 72 percent for women vs. 1,350 percent for men, according to an analysis of national data by Gilead Sciences Inc., the pharmaceutical company that makes Truvada. Cooper, who is 25 and cleans houses for a living, had never heard of PrEP when her new primary-care doctor suggested it. Her insurance policy - like most policies, public and private - covered it without question. The only side-effects – nausea and stomach ache – lasted two days. But she was well-aware of her community's fears of HIV.

"I'm from inner-city North Philadelphia. There is a big stigma," Cooper said. Taking a drug to protect against the sexually transmitted virus that causes AIDS evokes reactions such as, "People would be saying you're having a bunch of sex," she said.

It didn't help that Truvada was first approved in 2004 as part of the "cocktail" of anti-retroviral drugs to treat people with HIV.

The stigma suppresses conversation about HIV in African American neighborhoods, adding to the biggest challenge of getting PrEP to women, overcoming the belief that they don't need it.

"Very few of them feel that they actually are at risk," said infectious diseases physician Helen C. Koenig, medical director of PrEP for Philadelphia FIGHT's three community health clinics, where about 500 patients currently are prescribed the treatment, fewer than 10 percent of them women. The best-known risk factors, such as injection drug use and male-to-male sex, don't apply to them — and they may not know whether they apply to their partners.

Yet so many men in parts of North and Southwest Philadelphia are carrying the virus that women are at higher risk of contracting it during sex with men. The fact is, people often have no way of knowing everything a partner has been doing.

"Anyone on birth control should be offered PrEP.  And anyone with a recently sexually transmitted infection, or anyone who is using condoms inconsistently with someone of unknown HIV status," Koenig said.

Young women are more likely to have partners whose status is uncertain, even to them. Older black women, even those in their 50s or 60s, may be unaware that their husband has been sexually active with other women or with men, Koenig said. There is a "sort of don't ask, don't tell, particularly in the religious community," she said. Even when  women start on PrEP, the same issues may conspire to reduce their motivation to keep taking the daily pill, which  does not protect against pregnancy or other sexually transmitted diseases other than HIV.

"Condoms do both, but it requires the cooperation of the partner," said Erika Aaron, a nurse practitioner who serves as PrEP clinical adviser to the Philadelphia Department of Public Health. Guidelines recommend that condoms be used with PrEP.

At the city's Strawberry Mansion Health Center, heterosexual women who are on PrEP because their partner is HIV positive or has risk factors for the infection have reported that the regimen gives them more "peace of mind," Aaron said, and some say that improves their sexual experience, as well.

Women with HIV-positive partners who stop condoms and start PrEP in order to get pregnant – a process known as PrEP-ception — are particularly enthusiastic.

The Centers for Disease Control and Prevention has recognized that PrEP has the potential to help end the HIV epidemic, yet has not pushed it as heavily as condoms. Pharmaceutical manufacturer Gilead did not market Truvada for PrEP at all until a few months ago, instead putting its advertising dollars into more lucrative medications such as the hepatitis C drugs Sovaldi and Harvoni.

Teitelman – the family nurse practitioner who also is an associate professor at the University of Pennsylvania School of Nursing – is beginning a three-year study,  funded by the National Institute of Mental Health, on  increasing use of PrEP among high-risk women.

The study,  also led by Beryl A. Koblin of the New York Blood Center, will use in-depth interviews and surveys of heterosexual women in the two cities, which have different patterns of HIV. (Latino women are at higher risk in New York.)

Teitelman says she believes that this is the first study to focus specifically on women and PrEP. She already has a general idea of what these women, many of whom are poor and are likelier to be victims of violence, will need to succeed — starting with learning about PrEP. The women will be followed in a randomized trial to see whether a series of interventions, some as simple as text-message reminders to take a pill, might help them stay on the prophylactic treatment.

"We are not saying this is right for everybody," Teitelman said. "The biggest concern I have for women is that women should know about this and women don't know about it."

If they do, she said, "they can make a choice."