They prescribe Truvada within 72 hours to people who may have been exposed to hiv as a preventative measure to decrease likelihood of transmission. However, after 72 hours of exposure, Truvada won't work in preventing transmission anymore. The regime of one tablet a day must be started within 72 hours of exposure otherwise it won't be effective. They prescribe it to a lot of sexual assault victims as well as health workers that can get pricked by a contaminated needle. This shit is expensive, if you're not covered by health insurance a month supply is about $1000. Its relatively new so there is no generic alternative for it yet as well. This "breakthru" is good news. I just hope it doesn't give a false sense of security and people stop having safe sex and decide to just pop a pill daily.