HIV preexposure prophylaxis (PrEP), involving a daily dose of the HIV drug Truvada (tenofovir disoproxil fumarate and emtricitabine) or Descovy (tenofovir alafenamide fumarate and emtricitabine), can reduce the risk of getting HIV in gay and bisexual men by up to 99%. On the other hand, if you have HIV, having an undetectable viral load reduces the odds of infecting others to zero.