Can You Get HIV on PrEP? Understanding the Risks and Effectiveness

Taking PrEP but still concerned about HIV exposure? Learn how to protect yourself from HIV.

Yes, you can get HIV while on PrEP, but the risk is extremely low when the medication is taken as prescribed. Pre-exposure prophylaxis (PrEP) is one of the most effective ways to prevent HIV, reducing the risk of acquiring HIV through sex by approximately 99% with consistent use. However, PrEP does not provide absolute protection, and missed doses, delayed injections, or rare breakthrough infections can affect its effectiveness. Understanding how PrEP works, what influences your level of protection, and why regular HIV testing matters can help you stay protected.

Medical reviewed by Dr. Bethany Berrios, DNP, Chief Nursing Officer at DevotedDOc. This article is for educational purposes only and is not a substitute for personal medical advice. Always follow your healthcare provider’s instructions and do not start, stop, or change your PrEP medication without medical guidance.

Can You Get HIV While on PrEP?

Although PrEP is highly effective, HIV infection is still possible. PrEP works by maintaining medication levels that help prevent HIV from establishing an infection after exposure. When taken correctly, it provides strong protection, but no HIV prevention method is completely effective.

According to the NIH guidance on HIV prevention with PrEP, taking PrEP as prescribed substantially reduces the risk of acquiring HIV. Most infections reported among people using oral PrEP have been associated with inconsistent medication use, although rare infections have occurred despite apparently adequate protection.

A person may acquire HIV while taking PrEP if medication levels are insufficient at the time of exposure or, rarely, if the virus is resistant to the medications being used. This is why following the prescribed schedule and attending regular testing appointments are essential parts of prevention.

How Effective Is PrEP Against HIV?

PrEP effectiveness depends on the medication, how consistently it is used, and the type of HIV exposure. When taken as prescribed, PrEP reduces the risk of acquiring HIV through sex by approximately 99%.

The CDC guidance on PrEP effectiveness reports that FTC/TDF (Truvada or its generic equivalent) reduces the risk of acquiring HIV through injection drug use by at least 74% when taken as prescribed. Other PrEP medications, including injectable options, have not been adequately studied for preventing HIV through shared injection equipment.

PrEP works best when enough medication is present in the body before potential HIV exposure. Missing oral doses or receiving injections later than scheduled can reduce protection, depending on the medication and individual circumstances.

How Different PrEP Medications Affect Protection

Several FDA-approved medications are available for HIV prevention, including daily oral tablets and long-acting injections.

• Truvada: A daily oral medication containing emtricitabine and tenofovir disoproxil fumarate (FTC/TDF), with generic equivalents available.
• Descovy: A daily oral medication containing emtricitabine and tenofovir alafenamide (FTC/TAF). It is not approved for people at risk of acquiring HIV through receptive vaginal sex.
• Apretude: A long-acting cabotegravir injection generally administered every two months after the initiation schedule.
• Yeztugo: A long-acting lenacapavir injection administered every six months after the required initiation regimen.

The FDA’s approval of twice-yearly injectable PrEP expanded prevention options for people who may prefer less frequent dosing.

Each medication has specific eligibility requirements, dosing instructions, and monitoring needs. Your healthcare provider can help determine which option fits your health history, potential exposure, and ability to follow the treatment schedule.

What Are the Chances of Getting HIV on PrEP?

The chances of getting HIV on PrEP are very low when medication is used correctly. However, the exact risk cannot be represented by a single percentage for every person because it depends on factors such as adherence, exposure frequency, the type of exposure, and whether the virus has resistance to PrEP medications.

For example, someone taking daily oral PrEP consistently generally has much stronger protection than someone who frequently misses doses. Injectable PrEP can reduce the burden of daily medication, but injections must still be received according to the prescribed schedule.

Why Breakthrough HIV Infections Can Happen

A breakthrough HIV infection occurs when someone acquires HIV despite using PrEP with apparently adequate medication levels. These infections are rare but have been documented.

Research summarized by aidsmap on breakthrough HIV infections describes cases involving both oral and injectable PrEP. Some reported infections have involved HIV strains with resistance to the medications used for prevention.

However, not every HIV infection diagnosed during PrEP use represents a true breakthrough. Some occur when medication levels are insufficient because of missed doses, delayed injections, or other treatment interruptions.

Can HIV Become Resistant to PrEP?

HIV drug resistance occurs when genetic changes allow the virus to become less responsive to certain antiretroviral medications.

Resistance may be involved in some rare breakthrough infections. It can also develop when someone acquires HIV while using PrEP and continues taking prevention medication without knowing they are infected.

PrEP is not a complete treatment regimen for someone who already has HIV. If infection is suspected or confirmed, a healthcare provider must evaluate the situation and determine an appropriate HIV treatment plan.

What Happens If You Miss PrEP Doses?

Missing PrEP doses can reduce protection because medication levels may fall below what is needed to prevent HIV infection. The impact depends on the specific medication, how many doses were missed, and when potential exposure occurred.

For daily oral PrEP, consistent use is important for maintaining protection. For injectable PrEP, receiving scheduled injections on time helps prevent gaps in medication coverage.

If you miss doses or an injection appointment, contact your healthcare provider for instructions. Do not take extra tablets or independently change your injection schedule to compensate.

How Long Does PrEP Take to Become Effective?

Daily oral PrEP does not provide maximum protection immediately after the first dose. According to CDC clinical guidance, oral PrEP reaches maximum protective drug levels after approximately seven days of daily use for receptive anal sex and up to 21 days for receptive vaginal sex and injection drug use.

The time needed for protection may differ with injectable medications, and evidence is more limited for some exposure types. Follow your healthcare provider’s instructions about when protection is expected and whether additional prevention methods are needed.

Does PrEP Protect Against Every Type of HIV Exposure?

PrEP helps prevent HIV, but it does not protect against every sexually transmitted infection or eliminate every possible risk associated with sexual activity or injection drug use.

It does not prevent gonorrhea, chlamydia, syphilis, or other non-HIV sexually transmitted infections. Condoms and routine STI screening remain important parts of sexual health.

PrEP also does not replace safe injection practices. Avoiding shared needles, syringes, and other injection equipment reduces the risk of HIV and other bloodborne infections.

Does PrEP Protect Against HIV From a Partner With HIV?

PrEP can provide strong protection when a person without HIV has a partner who is living with HIV, particularly when the partner’s viral load is detectable or unknown.

However, a person living with HIV who takes treatment and maintains a sustained undetectable viral load does not sexually transmit HIV. This is known as Undetectable = Untransmittable (U=U).

The decision to use PrEP in a relationship may depend on personal preferences, other partners, and whether additional HIV prevention protection is desired.

HIV Testing While on PrEP: Why It Matters

Regular HIV testing is essential during PrEP use because the medication is intended for people who do not have HIV. Testing helps identify possible infections early and ensures that patients receive the correct medication regimen.

According to the CDC recommendations for HIV testing while on PrEP, routine follow-up for patients taking oral PrEP includes both HIV antigen/antibody testing and HIV-1 RNA testing at least every three months.

For patients receiving injectable cabotegravir (Apretude), the CDC recommends both tests at the one-month follow-up after the initial injection and at subsequent injection visits, generally every two months. This routine testing is important even when patients have no symptoms or known recent HIV exposure.

Why HIV Testing Requires More Than One Test

HIV antigen/antibody tests detect specific markers of HIV infection, while HIV-1 RNA tests detect genetic material from the virus. Using both tests helps healthcare providers identify infections that might not be detected by a single test, particularly during early infection.

PrEP medications can sometimes delay or alter the detection of HIV infection. For this reason, both tests are part of routine CDC-recommended follow-up for oral and injectable cabotegravir PrEP, rather than being reserved only for patients with suspected HIV infection.

Understanding HIV test results can help explain why regular testing and follow-up appointments remain important throughout PrEP use.

What Other Monitoring Is Needed?

PrEP monitoring may include kidney function testing for certain oral medications, hepatitis B screening, and routine STI testing. The exact requirements depend on the medication and individual health factors.

Our guide to PrEP lab work and monitoring explains what patients may expect before starting medication and during follow-up care.

Regular appointments also provide an opportunity to discuss side effects, missed doses, and whether your current prevention method continues to meet your needs.

What Should You Do If You Think You Have HIV While Taking PrEP?

If you believe you may have acquired HIV while taking PrEP, contact your healthcare provider promptly. This is especially important if you have missed doses, received an injection late, or developed symptoms that could be associated with acute HIV infection.

Early HIV symptoms may include fever, fatigue, sore throat, swollen lymph nodes, or a rash. However, these symptoms are not specific to HIV, and some people have no noticeable symptoms.

Your healthcare provider may recommend additional laboratory testing to evaluate a possible infection, even if your routine HIV antigen/antibody and HIV-1 RNA tests were recently negative.

Do not assume that continuing your usual PrEP regimen is sufficient if HIV infection is suspected. PrEP medications alone do not provide complete HIV treatment, and your healthcare provider may need to adjust your care plan.

What If You Had a Recent HIV Exposure?

If you are not adequately protected by PrEP and believe you may have been exposed to HIV, seek medical advice immediately.

Post-exposure prophylaxis (PEP) is an emergency HIV prevention treatment that must be started within 72 hours of a potential exposure, ideally as soon as possible.

Our guide to PEP after potential HIV exposure explains when this medication may be recommended and why prompt treatment matters.

PEP is not automatically necessary after every exposure while taking PrEP. A healthcare provider should assess your medication use, exposure circumstances, and whether additional treatment is appropriate.

Frequently Asked Questions About PrEP and HIV

Can you get HIV while on PrEP?

Yes, but the risk is extremely low when PrEP is taken as prescribed. Missed doses, delayed injections, and rare breakthrough infections can reduce protection.

How effective is PrEP against HIV?

PrEP reduces the risk of acquiring HIV through sex by approximately 99% when taken as prescribed. FTC/TDF (Truvada or its generic equivalent) also substantially reduces HIV risk from injection drug use.

Does PrEP prevent HIV completely?

No. PrEP is highly effective but does not guarantee complete protection. Following the prescribed schedule and attending regular HIV testing appointments remain important.

Can you get HIV if you miss one PrEP pill?

Missing one pill does not automatically mean you will acquire HIV, but missed doses can reduce protection depending on your dosing history and exposure circumstances. Ask your healthcare provider for guidance.

Can you get HIV from someone who is taking PrEP?

PrEP is used by people who do not have HIV, so taking PrEP does not mean someone has HIV. However, PrEP does not guarantee that a person remains HIV-negative, making regular testing important.

Can you get HIV while taking injectable PrEP?

Yes, although HIV infections during properly administered injectable PrEP are uncommon. Receiving injections on schedule and completing required HIV testing help maintain protection.

Does PrEP protect against other STIs?

No. PrEP helps prevent HIV but does not protect against infections such as gonorrhea, chlamydia, or syphilis. Condoms and routine STI screening remain important.

Get HIV Prevention Support With DevotedDOc

PrEP is one of the most effective tools available for preventing HIV, but maintaining protection requires the right medication, consistent use, and regular testing. Understanding the factors that influence PrEP effectiveness can help you make informed decisions about your sexual health.

DevotedDOc provides telehealth services that can help patients discuss HIV prevention, medication options, and appropriate follow-up care. A healthcare provider can review your risk factors, explain available PrEP options, and help determine which prevention approach fits your needs.

Ready to take the next step in HIV prevention? Schedule your online visit with DevotedDOc to discuss your options.