Learn More:
10 things you need to know about the pill to prevent HIV
http://www.vox.com/2014/7/14/5896887/explainer-about-the-pill-to-prevent-hiv-aids-Truvada
It's been called, simultaneously, a medicine to "end the HIV epidemic" and a "party drug:" Pre-exposure prophylaxis, or PrEP for short, refers to a daily antiviral treatment that prevents HIV.

Pre-exposure Prophylaxis (PrEP) for HIV Prevention
http://www.cdc.gov/hiv/pdf/PrEP_fact_sheet_final.pdf
Pre-exposure prophylaxis, or PrEP, is a way for people who do not have HIV to help prevent HIV infection by taking a pill every day.

US Public Health Service

http://www.cdc.gov/hiv/pdf/prepguidelines2014.pdf
PREEXPOSURE PROPHYLAXIS FOR THE PREVENTION OF HIV INFECTION IN THE UNITED STATES - 2014

WHO: People most at risk of HIV are not getting the health services they need
http://www.who.int/mediacentre/news/releases/2014/key-populations-to-hiv/en/#
Failure to provide adequate HIV services for key groups - men who have sex with men, people in prison, people who inject drugs, sex workers and transgender people - threatens global progress on the HIV response.