PEP After Possible HIV Exposure: Start as Soon as Possible Within 72 Hours
PEP (Post-Exposure Prophylaxis) is an emergency course of antiretroviral medicine for people who do not have HIV and want to prevent infection after…
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PEP (Post-Exposure Prophylaxis) is an emergency antiretroviral medicine, commonly known as emergency HIV medication, for people who do not have HIV and want to prevent HIV infection after a possible exposure. It must be started as soon as possible, within 72 hours, to counter the virus and reduce the chance of it entering the body, and it must be taken continuously for 28 days.
What Medicines Make Up PEP?
A specialist will choose the PEP regimen best suited to each individual. PEP is made up of three antiretroviral medicines. Today there are formulations that combine all three in a single pill, or keep them as separate pills, depending on the doctor's judgment. These antiretroviral medicines make treatment more convenient, reduce the problem of missed doses, and help prevent future drug resistance.
Who Should Receive PEP?
PEP is for people who are at risk of HIV infection or who think they have recently been exposed to HIV. You should see a doctor as soon as possible and take the medicine within no more than 72 hours. People who should receive PEP often have had a risk event, such as:
- people who used a condom during sex but the condom broke, tore, or slipped off
- people who had sex with someone living with HIV
- people who have recently been sexually assaulted
- people who had sex while unconscious
- people who shared needles with others
- people who had sex without protection
What Are the Steps to Get PEP?
Anyone who wants to use PEP for emergency HIV prevention must consult a specialist, who will take a history of the recent risk event. The doctor will then assess whether PEP is appropriate to prescribe, which requires a blood test to confirm that the person does not already have HIV, a screening for other sexually transmitted infections, a hepatitis B test, and liver and kidney function tests to make sure the person is truly ready to take PEP. After completing the full 28 days of medicine, the person must be tested for HIV again at 1 month, 3 months, and 6 months to confirm the result.
The Difference Between PrEP and PEP
| PrEP | PEP |
|---|---|
| Antiretroviral medicine taken before exposure | Antiretroviral medicine taken after exposure |
| Stops the virus from replicating in the body | Stops the virus from replicating before it can establish infection in the body |
| Taken only before a risk event | Used in emergencies, within 72 hours after exposure |
| Taken every day, one tablet a day | Taken once a day for 28 consecutive days |
| Suitable for people at ongoing risk of acquiring HIV | Suitable for people who have just had a risk event |
How Long Do You Take PEP?
PEP is taken once every day, following the regimen the doctor prescribes for each individual, and it must be taken continuously for 28 days.
How Much Does PEP Cost?
PEP is an expensive medicine, with prices starting from 1,200 to 20,000 baht depending on the type of medicine and the doctor's judgment. Several organizations also offer it free of charge for certain at-risk groups and programs.
Does PEP Have Side Effects?
Most people who take PEP do not experience serious side effects, because the medicine is safe for the body and accepted worldwide. For those who do have side effects, symptoms usually improve after about one week of taking the medicine. Noticeable symptoms may include:
- nausea
- dizziness
- fatigue
- diarrhea
What Percentage of HIV Infections Can PEP Prevent?
PEP can prevent more than 80% of HIV infections when it is taken in time, within no more than 72 hours. The sooner the medicine is taken, the more effective it is, and this also depends on the physical condition of the person taking it.
After Finishing the Full Course of PEP, Do You Need to See the Doctor Again?
After completing one month of PEP, it is essential for the person to see a doctor to test for HIV at 1 month, 3 months, and 6 months, to confirm that the PEP was effective at countering HIV in the body.
If You Do Not Complete the Full Course of PEP, Is There a Risk of Infection?
If you do not take the medicine for the full 28 days, or you miss doses on some days, the effectiveness of the protection will be reduced. You should consult a doctor for proper advice. If you have sex during this time, use a condom every time, and avoid behavior that carries a risk of infection until the doctor confirms through a blood test that there is no infection.
Do You Have to Take PEP Forever?
As noted above, PEP is used after a possible exposure to HIV and should only be used in emergencies, within 72 hours of the risk event. If you regularly lead a relatively high-risk lifestyle, it is better to use PrEP to reduce the chance of infection before exposure.
PEP cannot prevent HIV infection 100%, so you should use a condom every time you have sex to protect against HIV and other sexually transmitted infections.
Verified references
Links and relevance to the article’s main topic were reviewed on 13 August 2026. Each source supports only the scope stated in the original document and does not replace personalised medical, legal, or service advice.
- CDC: Clinical Guidance for PEP Accessed 13 August 2026
- CDC: 2025 nPEP Guidelines Accessed 13 August 2026
- WHO: HIV and AIDS fact sheet Accessed 13 August 2026
