Truvada, a pill that works to prevent the spread of HIV, has been the source of quite a bit of controversy as of late. And according to a report from UPI, a recent study has stirred the pot even further. Researchers at the University of North Carolina at Chapel Hill have found that women need more of the drug than men to effectively prevent infection.

Truvada is currently the only approved drug for the prevention of HIV infection. The study, published in the Journal of Infectious Diseases, suggested that while only two doses per week was sufficient for male patients, female patients needed a daily dose in order to effectively prevent HIV transmission.

The U.S. Food and Drug Administration approved the medication in 2012, and so far the results have been positive. Treating high-risk individuals with Truvada has resulted in a significant drop in the number of new HIV infections in places where the drug is easily obtainable.

Scientists examined the level of DNA material found in human cells that HIV could use as a means to reproduce and spread throughout the body. They calculated the amount of Truvada it would take to prevent an HIV infection based on the level of available material, and discovered a huge disparity between male and female patients.

To test their calculations, they gave 47 healthy women Truvada and took samples of vaginal, cervical, and rectal tissue. They tested for the levels of Truvada and DNA material present in each woman, and found that the drug was not making its way into vaginal and cervical tissues. They reasoned that the only way to deliver enough Truvada to these critical tissues was to increase the dosage to once a day.

Truvada has been hailed for its ability to stem the spread of HIV, but has also drawn controversy from critics who say it lulls high-risk individuals into a false sense of security. It certainly doesn’t hurt, but it is important to remain vigilant about sexual health risks on all fronts.

A press release from the University of North Carolina at Chapel Hill describing the details of the study can be found here.