Pre-Exposure Prophylaxis (PrEP) is a medication taken daily by people who are HIV-negative to prevent infection. This prevention tool works by keeping active drug compounds in the body that block the Human Immunodeficiency Virus (HIV) from establishing a permanent infection. While early awareness often centered on men who have sex with men, PrEP is a highly effective strategy for any person at substantial risk of acquiring HIV through sexual activity or injection drug use.
Understanding PrEP and Its Approved Scope
PrEP works at a molecular level, using a combination of antiretroviral drugs that interfere with the virus’s ability to replicate itself. If HIV enters the bloodstream, these drugs prevent the virus from copying its genetic material and spreading, which stops the infection from taking hold. The Food and Drug Administration (FDA) has approved PrEP for all individuals at substantial risk of sexual or injection-related HIV transmission, including heterosexual men and women.
The two primary oral PrEP regimens are TDF/FTC (tenofovir disoproxil fumarate and emtricitabine) and TAF/FTC (tenofovir alafenamide and emtricitabine). TDF/FTC is approved for all populations at risk, including those engaging in receptive vaginal sex. However, the TAF/FTC regimen is not currently approved for individuals whose primary risk comes from receptive vaginal sex. This is due to a lack of sufficient study data demonstrating adequate drug concentration in vaginal tissue. Cisgender women considering PrEP should discuss TDF/FTC or its generic equivalents with their healthcare provider.
Assessing HIV Risk for Heterosexual Individuals
PrEP is intended for heterosexual individuals whose behaviors or circumstances place them at a higher likelihood of acquiring HIV. A primary factor for considering PrEP is having a sexual partner who is HIV-positive and not consistently maintaining an undetectable viral load through treatment. PrEP should also be considered if a partner’s HIV status is unknown, particularly if that partner has known risk factors for the virus.
Other circumstances that increase risk include frequent unprotected sex with multiple partners, or a recent diagnosis of a bacterial sexually transmitted infection (STI) like syphilis or gonorrhea. The presence of an STI can create inflammation or breaks in the skin, making it easier for HIV to enter the body. Receptive vaginal sex carries a higher risk of transmission than insertive penile sex because of the larger surface area of exposure and extended contact with potentially infectious fluids.
Clinical Efficacy and Safety Monitoring
Multiple large-scale clinical trials have demonstrated the effectiveness of PrEP in heterosexual populations. The Partners PrEP Study, involving heterosexual couples where one partner was HIV-positive, showed that the TDF/FTC combination reduced the risk of HIV acquisition by approximately 75%. The TDF2 study also confirmed a significant risk reduction with daily PrEP use.
When the medication is taken consistently as prescribed, its effectiveness rises to roughly 99% in preventing sexually acquired HIV infection. This level of protection depends entirely on maintaining adherence to the daily dosing schedule. Most individuals tolerate PrEP well, with initial side effects typically being mild and temporary, such as nausea, headache, or stomach discomfort.
Potential side effects can involve measurable changes in kidney function or a slight decrease in bone mineral density. Due to these potential effects, a healthcare provider must monitor the individual’s health closely. This safety monitoring involves regular follow-up visits, typically every three months, which include blood tests to check for HIV infection and to assess kidney function.
Starting and Maintaining PrEP Therapy
Beginning PrEP therapy requires an initial consultation with a healthcare provider, such as a doctor, nurse practitioner, or a specialist at an HIV clinic. This first step involves baseline testing to confirm the person is HIV-negative before starting the medication. Testing also includes checking kidney function, screening for STIs, and checking for Hepatitis B status. Starting PrEP while unknowingly HIV-positive can lead to the virus developing resistance to the medication.
Once PrEP is started, protective drug levels build up in the body’s tissues over time, requiring strict daily adherence. For individuals engaging in receptive vaginal sex, it takes about 21 consecutive days of use to reach maximum protective levels. For anal sex, protection is typically achieved after seven days of daily use.
Maintaining PrEP requires a continuous commitment to taking the pill once every day, and attending all scheduled quarterly follow-up appointments. These visits are essential for repeat HIV testing, STI screening, kidney function checks, and receiving new prescriptions. Missing doses or neglecting follow-up appointments significantly lowers the drug concentration in the body, which reduces the level of protection against HIV acquisition.