taking PrEP medication are at risk for becoming resistant to emtricitabine. Consequently, people with HIV infection and resistance to emtricitabine will have fewer options for selecting HIV treatment medications. PrEP has been shown to be effective at reducing the risk of acquiring HIV in individuals at increased risk. However, PrEP is not 100% effective at preventing HIV, even in people who take the medication as prescribed. There have been several reported cases of people who acquired HIV despite taking PrEP. People taking PrEP may use combination prevention strategies along with PrEP, like condoms. If someone on PrEP acquires HIV, they may experience the signs and symptoms of HIV/AIDS. PrEP is typically taken continuously and daily following potential exposure. The CDC recommends follow-up visits at least every three months to provide HIV tests, medication adherence counseling, behavioral risk reduction support, side effect assessment, STI symptom assessment, and STI testing for sexually active individuals with symptoms of a current infection. Pregnancy tests should also be done every three months for woman who may become pregnant. At three months and every six months thereafter, renal function and presence of bacterial STI is assessed. Effectiveness of PrEP is associated with adherence, with effectiveness decreasing with suboptimal adherence. Although the daily, oral dosing schedule is still recommended for all individuals taking PrEP medication for HIV infection prevention, event-driven pre-exposure prophylaxis, or ED-PrEP, is an option for men who have sex with men. ED-PrEP is also referred to as "2+1+1" dosing, because the dosing regimen involves a person taking two pills two to twenty-four hours prior to sex, one pill twenty-four hours after taking the first two pills, and a last pill taken forty-eight hours after taking the first two pills. This dosing regimen was first proven effective to reduce the relative risk of HIV infection by 86% in the IPERGAY randomized clinical trial performed in Canada and France in 2015. This has only been evaluated with Truvada and not other drugs. According to the WHO, ED-PrEP should be considered for HIV infection prevention in men who have sex with men who have relatively infrequent sex, who are able to plan sex or delay sex for about two hours, and who find this dosing schedule convenient. ED-PrEP is not recommended for use in other populations, such as cisgender or transgender women and men who have vaginal and/or anal sex with women, due to the lack of