HIV pre-exposure prophylaxis (PrEP) is a biomedical HIV prevention strategy where HIV-negative individuals at substantial risk of HIV acquisition take antiretroviral medications to prevent infection. PrEP is highly effective when taken consistently — clinical trials and real-world data demonstrate 99%+ efficacy for sexual HIV prevention with high adherence, and approximately 74% efficacy among people who inject drugs. PrEP does not prevent other STIs and should be combined with safer sex practices.
Available regimens include: oral daily tenofovir disoproxil fumarate/emtricitabine (TDF/FTC, Truvada) — first-line, well-studied; oral daily tenofovir alafenamide/emtricitabine (TAF/FTC, Descovy) — alternative with better renal and bone safety, approved for MSM and transgender women but not for receptive vaginal exposure; on-demand or '2-1-1' dosing for MSM (2 pills 2-24 hours before sex, 1 pill 24 hours later, 1 pill 48 hours after first dose); long-acting injectable cabotegravir every 2 months (Apretude) for those preferring injection over daily pills. PrEP is recommended for MSM with multiple partners or condomless sex, transgender persons at risk, serodiscordant couples (especially when partner not virally suppressed), heterosexual individuals at substantial risk, and people who inject drugs.
Initiation requires: confirmed HIV-negative status (4th-generation antibody/antigen test, with HIV RNA if recent high-risk exposure), STI screening (chlamydia, gonorrhea, syphilis, hepatitis B and C), kidney function (creatinine, estimated glomerular filtration rate), hepatitis B serology (PrEP active against HBV, may suppress active replication), pregnancy testing for women of childbearing age, and counseling on adherence, side effects, and sexual health. Quarterly monitoring includes HIV testing, STI screening, kidney function, and adherence assessment. Common side effects include initial nausea (resolves typically within weeks), modest decrease in bone mineral density (clinically minimal), and rare nephrotoxicity (TDF). PrEP can be safely discontinued with appropriate tapering. Discontinuation requires HIV testing during the at-risk period.