HIV Prevention: PrEP, PEP, Condoms, and U=U Explained

HIV prevention has never been more effective. The combination of PrEP, condoms, treatment-as-prevention (U=U), and regular testing gives sexually active people a toolkit that, used correctly, makes HIV acquisition extremely unlikely. Understanding what each tool does — and what it doesn't do — is how you use them well.

Quick answer: PrEP (pre-exposure prophylaxis) reduces HIV acquisition risk by more than 99% when taken consistently. It requires a prescription and regular monitoring. Condoms provide additional STD protection that PrEP does not. If you had potential HIV exposure in the last 72 hours, PEP (post-exposure prophylaxis) can prevent infection — go to an ER immediately. Testing is how you know these strategies are working.

PrEP: Pre-Exposure Prophylaxis

PrEP is medication taken by HIV-negative people to prevent HIV infection before potential exposure. Two formulations are currently available in the US.

Daily oral PrEP (Truvada / generic tenofovir-emtricitabine): A once-daily pill that, when taken consistently, reduces the risk of sexually acquired HIV by more than 99%. It takes approximately 7 days to reach protective levels for receptive anal sex, and 21 days for receptive vaginal sex. Missing doses reduces effectiveness. It is also protective against HIV from injection drug use.

Cabotegravir injectable PrEP (Apretude): A long-acting injectable given every two months by a healthcare provider. Approved in 2021, it is at least as effective as daily oral PrEP and eliminates the daily adherence issue. After two initial monthly injections, it is given every 8 weeks. It requires clinic visits for each injection.

PrEP does not protect against any STD other than HIV. People on PrEP should continue to test for gonorrhea, chlamydia, syphilis, and hepatitis C regularly, as PrEP use is associated with reduced condom use in some populations, which increases risk for these infections.

Who Should Consider PrEP

PrEP is recommended for HIV-negative people at substantial risk of HIV acquisition. CDC guidelines suggest considering PrEP for: MSM (men who have sex with men) who have had anal sex without a condom or been diagnosed with an STD in the past 6 months; heterosexual men or women who have had sex without a condom with a partner whose HIV status is unknown or positive and who is not virally suppressed; people who inject drugs and have shared needles or equipment; and people whose partners are HIV-positive and not consistently on treatment.

PrEP is underutilised. Many people who would benefit from it have not been offered it or don't know about it. Any doctor can prescribe it — you don't need an infectious disease specialist. Telehealth PrEP prescribing is widely available and has significantly expanded access.

Getting PrEP

Starting PrEP requires an HIV test (to confirm negative status), a kidney function test (tenofovir affects kidney function at high doses; monitoring is required), and STD screening. Follow-up appointments every 3 months are standard while on PrEP: HIV test, kidney function (for oral PrEP), and STD screening at each visit.

Cost: With insurance that covers ACA-mandated preventive services, PrEP should have no out-of-pocket cost for the medication or associated clinical visits. Without insurance, manufacturer patient assistance programmes (Gilead's Advancing Access for Truvada/Descovy, ViiV's patient assistance for Apretude) cover costs for qualifying patients. Community health centres and Planned Parenthood offer PrEP programmes on sliding-scale or no-cost bases.

PEP: Post-Exposure Prophylaxis

PEP is a 28-day course of antiretroviral medication taken after a potential HIV exposure. It is not a substitute for PrEP or condoms — it is an emergency intervention for situations where exposure has already occurred.

PEP must be started within 72 hours of exposure to be effective, and ideally within 24 hours. Effectiveness decreases with every hour of delay. After 72 hours, PEP is not effective and should not be started. Go to an ER or urgent care — not a GP surgery where you might lose 24–48 hours to referral delays. Tell them you need PEP and when the exposure occurred.

Situations where PEP is appropriate: unprotected sex with a partner of unknown HIV status or a partner who is HIV-positive and not virally suppressed; a condom breaking during sex with a higher-risk partner; sexual assault; sharing needles with someone who is or may be HIV-positive.

Condoms

Male condoms, when used correctly and consistently, reduce HIV transmission risk by approximately 85% in real-world use (higher in perfect use studies). They provide protection against HIV, gonorrhea, chlamydia, syphilis, and other STDs that PrEP and ART do not cover. This is why condom use remains recommended even for people on PrEP, particularly for STD prevention rather than HIV prevention.

Correct use matters. Common errors: not using from start to finish, improper sizing, using oil-based lubricants with latex condoms (which degrade the latex), and not using lubricant at all with anal sex (which increases friction and condom breakage risk).

Treatment as Prevention: U=U

People with HIV who are on effective antiretroviral therapy and maintain an undetectable viral load cannot sexually transmit HIV to their partners. This is the U=U (Undetectable = Untransmittable) principle, established by the PARTNER studies and confirmed by multiple large-scale trials. For HIV-positive individuals on effective treatment, the risk to partners is zero for sexual transmission. This is relevant to understanding your actual risk when your partner discloses HIV-positive status.

Regular Testing

Testing is the foundation of all HIV prevention strategies. You cannot use PrEP appropriately without knowing you're HIV-negative. You cannot benefit from early treatment without knowing you're HIV-positive. You cannot practice U=U without confirmation of viral suppression. The CDC recommends HIV testing at least annually for all sexually active adults, and every 3 months for MSM with multiple partners or who are on PrEP.

Frequently Asked Questions

Can I start PrEP the same day I ask for it?

In many cases, yes. Some clinics offer same-day PrEP initiation after rapid HIV testing and a brief clinical assessment. Injectable cabotegravir requires two initial monthly injections before moving to the 8-week schedule. If you're at immediate risk, don't delay seeking a prescription.

Does PrEP cause side effects?

Some people experience mild GI side effects (nausea, headache) in the first 2–4 weeks of oral PrEP, which typically resolve. Long-term, tenofovir at PrEP doses has a good safety profile in most people. Kidney function and bone density are monitored. Cabotegravir injectable is generally well tolerated; injection site reactions are the most common side effect.

Is PrEP only for gay men?

No. PrEP is indicated for any HIV-negative person at substantial risk of HIV acquisition, regardless of sexual orientation or gender. Heterosexual men and women, transgender people, and people who inject drugs all benefit from PrEP when they are at risk. Uptake in heterosexual populations and women has historically been lower than needed — providers should offer it proactively to all high-risk patients.

What's the difference between PrEP and PEP?

PrEP is taken before potential exposure, continuously, to prevent HIV. PEP is taken after a specific exposure has occurred, as an emergency intervention. They use different drugs and different timelines. PrEP is not effective as PEP — if you've had a potential exposure, you need actual PEP, not just PrEP.

If I'm on PrEP, do I still need to use condoms?

PrEP protects against HIV only. Condoms protect against gonorrhea, chlamydia, syphilis, herpes, HPV, and other STDs. For HIV prevention alone, PrEP is highly effective without condoms. For overall STD prevention, combining PrEP with condoms provides broader protection. The decision is yours to make with your provider based on your specific risk profile.

Related: Understanding HIV · STD Testing for LGBTQ+ · STD Testing: What You Need to Know · How Often Should You Get Tested? · Get tested today →