Pre-Exposure Prophylaxis (PrEP) is a medication-based strategy that has significantly changed HIV prevention. PrEP refers to taking antiretroviral medication before potential exposure to the Human Immunodeficiency Virus to prevent infection. The question of whether a person using PrEP can transmit HIV touches upon a common point of confusion regarding modern prevention methods. Understanding how PrEP works and differentiating it from treatment for people already living with HIV clarifies the answer.
What PrEP Is and Who Takes It
PrEP is specifically prescribed for individuals who are HIV-negative but are at a higher risk of acquiring the virus through sexual contact or injection drug use. The medication, typically a combination of two antiretroviral drugs like tenofovir and emtricitabine, works inside the body to create a protective barrier. If HIV enters the bloodstream, these drugs interfere with the virus’s ability to replicate by blocking an enzyme the virus needs to make copies of itself.
This mechanism stops the infection before it can take hold. The person taking PrEP is, by definition, HIV-negative throughout the entire course of treatment. PrEP is a powerful tool to prevent the acquisition of the infection, not a cure for HIV. Therefore, an individual taking PrEP as prescribed and confirmed to be HIV-negative cannot pass HIV to a partner.
How Effectively PrEP Prevents HIV Acquisition
PrEP is highly effective at preventing the user from contracting HIV, provided it is taken consistently as directed. For individuals who take the pill form of PrEP every day, the risk of getting HIV from sexual contact is reduced by about 99%. This protection demonstrates the drug’s ability to neutralize the virus upon exposure before it can establish a systemic infection.
The effectiveness relies on maintaining sufficient drug levels in the bloodstream and tissues, which makes adherence important. Among people who inject drugs, PrEP reduces the risk of acquiring HIV by at least 74% when taken consistently. When adherence is perfect, cases of HIV acquisition are extremely rare.
Clarifying PrEP and Undetectable Equals Untransmittable
Confusion about transmission often stems from conflating PrEP with Treatment as Prevention (TasP) or the concept known as Undetectable Equals Untransmittable (U=U). PrEP is for people who are HIV-negative, while TasP and U=U apply to people who are living with HIV. TasP involves an HIV-positive person taking antiretroviral therapy (ART) to improve their health and prevent transmission.
When a person living with HIV adheres to treatment, their viral load can drop to an extremely low level, called an undetectable viral load. This U=U status means the virus is so suppressed that it cannot be sexually transmitted. Research has conclusively shown that people who maintain an undetectable viral load cannot pass the virus through sex.
The difference is simple: a person on PrEP is HIV-negative and cannot transmit the virus because they do not have it. A person with an undetectable viral load is HIV-positive but cannot transmit the virus due to the effectiveness of their treatment. Both strategies use antiretroviral drugs but serve different populations.
Adherence and Monitoring: Ensuring PrEP Works
For PrEP to maintain its high level of protection, consistent adherence to the prescribed regimen is necessary. This means taking the pill every day for daily oral PrEP, or following an “on-demand” schedule if prescribed. Missing doses causes drug levels to drop, compromising the protective barrier and increasing the risk of acquiring HIV.
Regular monitoring is a necessary component of PrEP use, typically involving follow-up visits with a healthcare provider every three months. At these appointments, patients must undergo an HIV test to confirm they remain HIV-negative. This routine testing is a safeguard, ensuring that if an infection occurred, it is caught early to prevent drug resistance and allow for immediate treatment.
Monitoring also includes assessing for side effects and testing for other sexually transmitted infections, as PrEP only protects against HIV.