HIV Prevention: A Medically Reviewed Guide
Medically Reviewed: Dr. Nattaphon Luchaichana (Dr. Dear), M.D.Medical License No. 52558 | Board Certification 47184/2566 (Urology) | Physician at Menness Clinic
Key Takeaways
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1. HIV in the Modern Era: Preventable, Treatable, and Should Not Be Stigmatized
HIV (Human Immunodeficiency Virus) is a virus that damages the immune system. Today, however, antiretroviral therapy (ART) is highly effective. People living with HIV who receive consistent treatment can, in many cases, achieve a health status and life expectancy close to that of the general population.
Another key concept is U=U (Undetectable = Untransmittable). When a person with HIV takes antiretroviral medication consistently and maintains a viral load below the threshold used for sexual-transmission prevention (generally HIV RNA <200 copies/mL), they will not transmit HIV to sexual partners. The goals of HIV care today therefore include preventing new infections, enabling early diagnosis, and linking people who test positive to ongoing treatment.
2. HIV Testing: Understanding the “Window Period” Correctly
Knowing your HIV status is an essential starting point — especially before starting PrEP or after a risk exposure. However, the time it takes for a test to detect infection depends on the type of test used.
Test Type | Typical Detection Window After Exposure | Notes |
4th-generation Ag/Ab (venous blood, lab-based) | ~18–45 days | Best option when trying to shorten the window period |
Rapid Ag/Ab (fingerstick) | ~18–90 days | Detection window may be longer than venous blood tests, depending on the test kit |
HIV NAT / HIV RNA | ~10–33 days | Considered for suspected acute HIV or very high-risk cases, at physician discretion |
Important: It is inaccurate to state broadly that 4th-generation tests have a window period of only 14–21 days, since performance varies by specimen type and test kit. If tested too early, repeat testing may be needed as advised by a physician. Some rapid test kits can deliver results in about 20–30 minutes, but result turnaround time and window period are two different things — refer to the specific test kit used by the clinic in question.
Before starting PrEP, HIV infection must be ruled out, along with an assessment appropriate to the chosen regimen — for example, kidney function for oral PrEP regimens containing tenofovir — plus screening for hepatitis B and other STIs as appropriate.
3. Evidence-Based HIV Prevention
The World Health Organization uses the concept of Combination HIV Prevention — selecting multiple evidence-based measures suited to each person's risk and context, rather than a single fixed approach for everyone.
3.1 Condoms: Protect Against HIV and Multiple STIs
Correct and consistent condom use is a key method for reducing the risk of HIV and STIs transmitted through bodily fluids, such as gonorrhea and chlamydia.
However, the commonly cited figure of “98% protection against HIV” should not be applied broadly — that figure is typically drawn from contraceptive efficacy with perfect use, not a standard HIV-prevention efficacy figure. CDC data estimates that consistent condom use among heterosexual couples with differing HIV status reduces risk by approximately 80% compared with no condom use.
Condoms also provide incomplete protection against infections spread through skin not covered by the condom, such as HPV, herpes, and some cases of syphilis — so STI testing based on individual risk remains important.
3.2 PrEP: Prevention Before Exposure
PrEP (Pre-Exposure Prophylaxis) is the use of antiretroviral medication by HIV-negative individuals to prevent infection before exposure. It is suited for people with a realistic chance of HIV exposure through sex or other risk factors, and the regimen can be tailored to the individual based on available guidelines and medications.
When used consistently as directed, PrEP reduces the risk of sexually acquired HIV by approximately 99%. However, PrEP does not protect against gonorrhea, syphilis, chlamydia, or pregnancy, so condoms still play an important role.
Before starting the medication, a physician must confirm the person does not have HIV, because if someone is already infected — especially during acute HIV infection — using a PrEP regimen that is insufficient for treatment could increase the risk of drug resistance.
3.3 PEP: Prevention After a Risk Exposure
PEP (Post-Exposure Prophylaxis) is antiretroviral medication used after an event that may have exposed someone to HIV, such as unprotected sex, a broken or slipped condom, or blood exposure in a high-risk situation.
The key principle is to start medication as soon as possible — ideally within 24 hours if possible, and no later than 72 hours after exposure. Current guidelines recommend taking the medication continuously for 28 days.
PEP cannot guarantee 100% protection, and starting it should not be delayed while waiting for all laboratory results, if a physician assesses that the exposure warrants PEP.
3.4 U=U: Treating People With HIV Is Also a Form of Prevention
For couples with differing HIV status, if the partner with HIV receives ART consistently and maintains a viral load meeting the U=U threshold, they will not transmit HIV through sex. This is among the strongest pieces of evidence in modern HIV prevention.
3.5 Circumcision: Beneficial, But Must Be Explained Accurately
Male circumcision has evidence from randomized controlled trials showing it can reduce men's risk of acquiring HIV from heterosexual sex (heterosexually acquired HIV) by approximately 50–60%.
The WHO therefore recommends voluntary medical male circumcision as a supplementary measure in areas with high HIV prevalence where heterosexual transmission is the primary driver — this does not mean circumcision is a necessary HIV-prevention method for every man, or that it can replace PrEP and condoms.
The mechanisms believed to be involved are multifactorial, including reduction of the inner foreskin tissue that contains HIV target cells, and changes to the local environment and inflammation beneath the foreskin. The mechanism is not explained solely by “the formation of a thicker keratin layer.”
4. Care at Menness Clinic
Menness Clinic provides private consultations on sexual health and men's health. Physicians assess individual risk and select an approach suited to each person — from HIV/STI testing and pre-PrEP evaluation, to PEP provision after a risk exposure, and assessing indications and options for circumcision.
For circumcision, the physician evaluates foreskin anatomy, underlying conditions, current medications, and equipment suitability before the procedure, and explains the benefits, limitations, and possible complications. Circumcision today is a minor surgical procedure — low pain, quick, and low blood loss — comparable to circumcision using assisted devices or “bloodless” circumcision techniques, which tend to have more complications related to wound care.
Frequently Asked Questions (FAQ)
Q: How effective is PrEP at preventing HIV?
A: When used as directed, PrEP reduces the risk of sexually acquired HIV by approximately 99%, but it does not protect against other STIs or pregnancy — so condom use should still be considered.
Q: Why do I need an HIV test before starting PrEP?
A: Because PrEP is intended for people who do not have HIV. If someone is unknowingly already infected — especially during acute HIV infection — using a regimen insufficient to treat HIV may increase the risk of drug resistance. Proper evaluation and testing are required before starting.
Q: Does PrEP have side effects?
A: Most users tolerate it well. Some may experience nausea, headache, or gastrointestinal symptoms initially. Certain tenofovir-based regimens may affect kidney function or bone density, so evaluation before starting and ongoing monitoring are recommended. The appropriate regimen and method should be chosen individually.
Q: What should I do if a condom breaks or I have unprotected sex?
A: If there is a possible HIV exposure, see a physician or a PEP-providing service as soon as possible — don't wait to see if symptoms develop. Starting PEP within 24 hours is ideal, and it must not exceed 72 hours after exposure. If cleaning is needed, gently wash with water and mild soap; douching or using strong disinfectants is not necessary.
Q: Does circumcision help prevent HIV?
A: It helps reduce risk partially. The strongest evidence is a reduction in HIV acquisition among men from heterosexual sex of approximately 50–60%, so it is considered a supplementary measure — not 100% protection — and should not be used in place of PrEP or condoms.
Q: How much does PrEP cost at Menness Clinic?
A: PrEP starts at approximately 990 THB per bottle for about one month's supply, depending on the regimen and physician's assessment. First-time users may have additional costs for HIV testing and necessary laboratory work. Please confirm current pricing and packages with the clinic before receiving services.
Main References
CDC. Clinical Guidance for PrEP (updated Apr 30, 2026). https://www.cdc.gov/hivnexus/hcp/prep/index.html
CDC. Antiretroviral Postexposure Prophylaxis After Sexual, Injection Drug Use, or Other Nonoccupational Exposure to HIV — United States, 2025. MMWR. https://www.cdc.gov/mmwr/volumes/74/rr/rr7401a1.htm
CDC. HIV Risk and Prevention Estimates. https://www.cdc.gov/hivpartners/php/riskandprevention/index.html
CDC. How Do I Know if I Have HIV? — HIV testing window periods. https://hivrisk.cdc.gov/how-do-i-know-if-i-have-hiv/
CDC. Preventing HIV with Condoms. https://www.cdc.gov/hiv/prevention/condoms.html
WHO. Consolidated guidelines on HIV prevention, testing, treatment, service delivery and monitoring — Combination HIV prevention. https://iris.who.int/bitstream/handle/10665/342899/9789240031593-eng.pdf?sequence=1
WHO. Voluntary medical male circumcision for HIV prevention. https://www.who.int/teams/global-hiv-hepatitis-and-stis-programmes/hiv/prevention/voluntary-medical-male-circumcision
Dinh MH, et al. The biology of how circumcision reduces HIV susceptibility: broader implications for the prevention field. Curr Opin HIV AIDS. 2017. https://pubmed.ncbi.nlm.nih.gov/28893286/
Jin XD, et al. Adult male circumcision with a circular stapler versus conventional circumcision: a prospective randomized clinical trial. Braz J Med Biol Res. 2015. https://pubmed.ncbi.nlm.nih.gov/25831203/
Huo ZC, et al. Use of a disposable circumcision suture device versus conventional circumcision: a systematic review and meta-analysis. Asian J Androl. 2017. https://pubmed.ncbi.nlm.nih.gov/26975486/
Thailand Department of Disease Control, Ministry of Public Health. PrEP/PEP and HIV prevention data.
