The medicine needs to build up in your body until it’s at high enough levels to protect against HIV. The drug builds up more quickly in rectal tissue, compared to vaginal tissue and blood. When starting PrEP, take it for at least 7 days before you engage in anal sex to be fully protected. You need to take it for at least 21 days before vaginal sex or IV drug use. Use barrier protection and/or avoid
sharing injection supplies during this time. Before you stop taking PrEP, wait 4 weeks after your last sexual encounter since you may have had contact with someone with HIV.