Glossary
On-Demand PrEP (2-1-1)
On-demand PrEP, also called 2-1-1 or event-driven PrEP, is a way of taking HIV prevention pills only around the time of sex rather than every day.
On-demand PrEP is a dosing schedule for HIV pre-exposure prophylaxis that ties the pills to sex instead of a daily routine. The "2-1-1" name describes the timing: two pills taken 2 to 24 hours before sex, one pill 24 hours after the first dose, and one more pill 24 hours after that. It uses the tenofovir disoproxil fumarate and emtricitabine combination (Truvada or its generics). The approach was studied mainly in gay and bisexual men and other men who have sex with men, where the French IPERGAY trial found it reduced HIV risk by about 86 percent. Later research such as PREVENIR found it worked as well as daily PrEP. On-demand PrEP is not recommended for people at risk through receptive vaginal sex.