PrEP and PEP: Are They the Same or Different, and Do They Really Prevent HIV?

PrEP and PEP are another way to prevent HIV by using medicine to guard against infection, though they differ in their purpose and in how they are used. PrEP (pre-exposure prophylaxis) is medicine used before potential exposure; when taken as prescribed, it reduces the risk of acquiring HIV through sex by about 99% and does not prevent other STIs. PEP (post-exposure prophylaxis) is an antiretroviral medicine that must be taken within 72 hours after exposure to the virus; it is used to reduce the risk of HIV infection and can lower that risk by more than 80% when taken consistently.

What are PrEP and PEP?

PrEP (Pre-Exposure Prophylaxis)

• A medicine used to protect against HIV before exposure.
• Taken every day, at the same time, one tablet a day.
• Should be used together with condoms so that you are protected against both HIV and other sexually transmitted infections.
• Can be stopped once you find that you are no longer at risk.

PEP (Post-Exposure Prophylaxis)

• A medicine used to protect against HIV in emergency situations.
• For people who have had sex without a condom, or whose condom slipped off, broke, or leaked.
• Must be started within 72 hours after exposure.
• Taken continuously for 28 days.

Thinking about PrEP? Talk with a provider near you * Prices and free services vary by provider. Please check the details before booking. Find a provider → 02

Who are PrEP and PEP for?

PrEP

• People who change sexual partners frequently.
• People who have sex with someone living with HIV.
• Men who have sex with men.
• People who have frequently needed to use PEP.
• People who share needles with others.

PEP

• People who have had sex without a condom.
• People whose condom slipped off, broke, or leaked.
• People who have had sex with someone living with HIV.
• People who have recently experienced sexual assault.
• People who had sex while not conscious.
• People who have shared needles with others.

How much do PrEP and PEP cost?

PrEP

The National Health Security Office (NHSO) has announced an important new benefit for Thai citizens by including PrEP (pre-exposure prophylaxis) for HIV prevention as one of the services covered under the national health security system. This is a significant step toward reducing the spread of HIV in Thailand and toward promoting equitable access to health services for populations at higher risk.

In Thailand, PrEP is widely available and can be accessed through healthcare providers, clinics, and various organizations. The options include:

• Provincial hospitals: Government hospitals in major cities and provinces offer PrEP services.
• Non-governmental organizations (NGOs).
• Private clinics.
• Or book an appointment online through Love2test for free here.

PEP

• PEP is an emergency antiretroviral medicine, and its price varies by facility, starting from 1,200 to 20,000 baht depending on the type of medicine and the doctor's judgment.

How to take PrEP and PEP

PrEP – Daily PrEP

• Start taking it 7 days before a potential exposure.
• Take one tablet a day.
• Every day, and at the same time.

On-Demand PrEP

• Take the first 2 tablets 2–24 hours before sex.
• Take 1 tablet 24 hours after the first dose.
• Take another tablet 48 hours after the first dose.

PEP (emergency antiretroviral)

• Take it as soon as possible, within 72 hours after exposure.
• Take one tablet a day, at the same time each day.
• Take it continuously for 28 days.

Find a PrEP service that fits your needs * Prices and free services vary by provider. Please check the details before booking. View PrEP services → 03

Side effects of PrEP and PEP

PrEP (Pre-Exposure Prophylaxis)

• Common side effects at the start include nausea, headache, diarrhea, and fatigue, which usually improve once the body adjusts to the medicine.
• In some cases it may affect kidney and bone function, but this is uncommon and tends to occur in people who take the medicine for a long time. Doctors monitor kidney function regularly to reduce this risk.

PEP (Post-Exposure Prophylaxis)

• PEP's side effects are similar to PrEP's, such as nausea, fatigue, diarrhea, and headache.
• Some people may feel dizzy or have digestive problems during the course of the medicine, which must be taken for 28 days.

Other articles you may find interesting

• How can I prevent HIV?
• How do you choose the right condom size? The importance of choosing the correct size

In summary, PrEP (pre-exposure prophylaxis) and PEP (post-exposure prophylaxis) are effective ways to prevent HIV infection. PrEP is for people at higher risk of infection and must be taken every day to prevent it, while PEP is used in emergency situations after a possible exposure and must be started within 72 hours of contact. Both methods help reduce the risk of HIV infection, but they should be used together with other forms of protection, such as condoms, for the greatest possible protection against the disease.

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.

1. CDC: Clinical Guidance for PrEP Accessed 13 August 2026
2. CDC: Clinical Guidance for PEP Accessed 13 August 2026
3. CDC: 2025 nPEP Guidelines Accessed 13 August 2026