HIV Pre-exposure Prophylaxis (PrEP) and Post-exposure Prophylaxis (PEP) Basics
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What are PrEP and PEP?
PrEP (pronounced like the first syllable in “preparation”) and PEP (pronounced like the first syllable in “pepper”) are medications that decrease the likelihood of becoming infected with human immunodeficiency virus (HIV) if exposed to it. Both medications are meant to be used by people who are not HIV positive. When taken as prescribed, PrEP reduces the risk of becoming infected with HIV from sex and intravenous drug use by 99 percent and at least 74 percent, respectively. Observational studies suggest that PEP can reduce the risk of becoming infected with HIV by more than 80 percent under real-world conditions where people miss doses and likely by much more when used as prescribed.
How are PrEP and PEP used?
In the United States, PrEP is approved as a daily oral pill and as a long-acting injectable. The two versions of the pill form combine different antiretroviral medications; the injectable version must be administered by a health care provider every two months.
Time is of the essence for beginning PEP, as a person must start the regimen as soon as possible within 72 hours of a known or possible HIV exposure. The Centers for Disease Control and Prevention (CDC) recommends several different combinations of three antiretroviral medications depending on age and health status. A person using PEP must take the prescribed combination of oral medications for a full 28 days to maximize its effectiveness. Importantly, PEP is not a substitute for PrEP and is not intended for use outside of emergency situations.
Who can benefit from PrEP and PEP?
The CDC recommends that health care providers prescribe PrEP to anyone who asks to use it, regardless of their HIV exposure risk or age. Oral PrEP is considered safe for use during pregnancy and the postpartum period. People who are particularly likely to benefit from PrEP include those who share equipment used to inject drugs, those with sexual partners whose HIV status is positive or unknown, and those who have had another sexually transmitted infection (STI) in the preceding six months.
PEP should be considered for people without HIV who may have been exposed during sex, injection drug use, an accidental injury or needle stick, sexual assault, or any other situation presenting a substantial risk of HIV exposure. PEP is also safe for use during pregnancy.
How are PrEP and PEP prescribed?
PrEP and PEP can be prescribed by a physician or advanced practice provider. In addition, some states allow pharmacists to prescribe these medications directly to a patient without consulting another health care provider. PEP is often prescribed when a patient visits an emergency room or urgent care center.
Before starting PrEP or PEP, a patient should be tested to confirm they do not have HIV, as these medications are not appropriate for people who are HIV positive. Testing for other STIs is also required. In addition, depending on the specific medications prescribed, a health care provider may also require kidney function, hepatitis B and C, and/or cholesterol tests. Routine HIV, STI, and kidney function tests are also required for patients to continue taking PrEP. Similarly, follow-up care for PEP includes three to six months of periodic HIV testing and, in some cases, kidney function and STI testing.
| Prep regimens | who can use them |
|---|---|
| Daily oral PrEP (Truvada® and generic versions) | All people at risk of HIV from sex or injection drug use |
| Daily oral PrEP (Descovy®) | Men and transgender women at risk of HIV from sex |
| Injectable PrEP (Apretude®) | All people over 77 pounds at risk of HIV |
| “Intermittent,” “event-based,” or “off-label” oral PrEP (2-1-1 schedule) | Men who have anal sex with men |
How do PrEP and PEP work?
Retroviruses, including HIV, cause disease by entering a person’s cells and using existing systems to insert the virus’ genetic material into their DNA. This allows the virus to make more copies of itself and infect more cells. PrEP and PEP work by preventing HIV replication so the immune system can clear the virus before it permanently establishes itself in the body.
For PrEP and PEP to work optimally, the medications must remain at sufficiently high concentrations in the body—which is why taking them as prescribed is so important.
Can PrEP and PEP be harmful?
Long-term PrEP use is considered safe. Some people may experience side effects like gastrointestinal upset, headache, and fatigue, which often decrease with time. Kidney function may decrease slightly while on PrEP, which is why regular kidney function testing is required; however, these changes usually do not affect a patient’s health. One formulation of PrEP can increase cholesterol, necessitating cholesterol monitoring as well. For most people who choose to take PrEP, the benefit of decreasing the likelihood of getting HIV outweighs the risk of side effects or adverse health outcomes.
People taking PEP also sometimes experience gastrointestinal upset and fatigue. More serious side effects have been reported but are rare.