PrEP and PEP: How to different, HIV medications and use them correctly

Have you ever made “one mistake” and then had to anxiously wait for weeks to find out if you’ve contracted HIV? Good news! We no longer have to live with such risks. We now have effective tools to “prevent in advance” or “stop the infection in time,” namely PrEP and PEP.

Many people are still confused about the differences between PrEP and PEP. When should they be used? Which one is right for you? This article will provide a simple explanation to help you confidently plan your prevention strategy.

What are PrEP and PEP?

PrEP and PEP are antiretroviral drugs with the primary goal of preventing HIV infection. However, they differ in their “timing of use” and “appropriate situations,” which are crucial points to understand clearly before deciding which to use.

What is PrEP?

PrEP (Pre-Exposure Prophylaxis) is a medication for preventing HIV before exposure to risk, such as unprotected sex with a partner whose HIV status is unknown, or engaging in repeated high-risk behaviors.

The principle of PrEP is to take the medication continuously to maintain sufficient drug levels in the body to prevent HIV from entering cells. The commonly used medication is Tenofovir + Emtricitabine, which is the same formula as antiretroviral drugs used to treat HIV-infected individuals, but in this case, it is used for “prevention” in advance.

• Must be taken at least 2 – 24 hours before potential exposure for men, and 7 days for women.
• Continuous daily intake is required to maintain effectiveness.
• Suitable for groups with regular risk behaviors, such as sero-discordant couples (one partner is HIV-positive), men who have sex with men (MSM), individuals with multiple sexual partners, or those who have sex with partners of unknown HIV status.
• Blood tests are required beforehand for safety every time.

What is PEP?

PEP (Post-Exposure Prophylaxis) is a medication for preventing HIV after exposure to risk, such as forgetting to use a condom, condom breakage, sexual assault, needle-stick injuries from an infected person in a healthcare setting, or uncertainty about condom use due to intoxication.

PEP helps inhibit HIV from establishing an infection in the body if started immediately after exposure and within 72 hours.

• Must take the medication continuously for 28 days.
• The sooner it’s started, the higher the chance of prevention (it is recommended to start within 2 hours if possible).
• Typically used in emergency situations and not suitable for regular use.
• Blood tests are required beforehand for safety every time.

How are PrEP and PEP Different?

Although PrEP and PEP share the same goal of “HIV prevention,” the key differences lie in the timing of use, method of administration, duration of treatment, and appropriate user groups.

Why is PrEP important for HIV prevention?

Currently, we have effective antiretroviral drugs that can “control” HIV infection. However, what’s even better is preventing infection in the first place, and PrEP is one of the best tools. It can prevent HIV infection by up to 99% if used consistently and correctly, especially in high-risk groups such as:

• Individuals with multiple sexual partners who cannot consistently use condoms.
• Sero-discordant couples (where one partner is HIV-positive).
• Men who have sex with men (MSM).
• People who inject drugs.
• Women or men engaged in sex work.
• Individuals who have previously used PEP and continue to have ongoing risks.

Therefore, using PrEP is not just about “self-protection” but also helps reduce the spread of the infection in society.

Does PrEP prevent only HIV or other diseases as well?

PrEP only prevents HIV infection. It does not prevent other sexually transmitted infections (STIs) such as syphilis, gonorrhea, chlamydia, HPV (warts), herpes, or some types of viral hepatitis (e.g., B and C). Therefore, even when using PrEP, it is still advisable to use condoms every time for comprehensive protection.

Why is PEP important in emergency situations?

PEP is crucial after exposure to HIV risk to prevent the virus from establishing itself in the body, which requires speed and adherence.

When should PEP be used immediately?

• Sexual assault.
• Unprotected sex with someone of unknown HIV status.
• Condom breakage or slippage during sex.
• Wound contact with blood/body fluids from an infected person.
• Healthcare personnel with needle-stick injuries from an infected person.

In all cases, PEP should be started within 72 hours after exposure, and ideally as soon as possible, within 2 hours for the best efficacy.

What are the limitations or precautions of PEP?

While PEP can reduce the chance of HIV infection by 80-90%, it is not a “magic bullet” and has important precautions:

• Must take the medication for the full 28 days; do not stop halfway.
• Repeat HIV testing after completing the medication (generally within 4-6 weeks).
• Side effects may occur, such as nausea, fatigue, or abdominal pain.
• Should not be used with certain medications. Always inform your doctor before starting any new medication.

PEP is a good option “when there’s no opportunity to prepare.” So, don’t wait for an incident to happen before taking preventive measures. If you have ongoing risk behaviors, planning ahead with PrEP is more suitable in the long run.

PrEP and PEP vs. Other Prevention Methods: How Do They Differ?

Who should use PrEP?

According to guidelines from the World Health Organization (WHO) and research in many countries, the following groups are considered suitable for serious consideration of PrEP:

• Men who have sex with men (MSM), especially if condoms are not used consistently.
• Sero-discordant couples (where one partner is HIV-positive), even if the infected partner is on treatment, PrEP can provide additional reassurance if there are concerns.
• Women/men with multiple sexual partners or who engage in unprotected sex.
• Sex workers.
• Individuals who have previously received PEP; if ongoing risk behaviors persist, it is recommended to consider switching to PrEP instead.
• People who inject drugs and share needles.
• Individuals in life transitions, such as stopping condom use, having a new partner, or frequent travel.
• Can the general public use PrEP? Yes, as long as they feel there “might be a risk” in the near future or are unsure of their partner’s status.

Who should use PEP?

In “emergency situations” when there is unintentional exposure to HIV and no opportunity to prepare in advance.

If you forget to protect yourself, when should you start PEP?

Immediately or within 72 hours after exposure is the effective timeframe. The sooner it’s started, the greater the chance of preventing infection (within 2 hours is best). If more than 72 hours have passed, the medication will no longer be fully effective in preventing infection.

Common situations include:

• Forgetting to use a condom during sex.
• Condom breakage or slippage.
• Uncertainty about a partner’s HIV status.
• Accidental contact of a wound with blood or bodily fluids from another person.
• Needle-stick injuries from an infected person in a healthcare setting.
• In cases of sexual assault, PEP must be started immediately without waiting for the other party’s test results.

How do PrEP and PEP prevent HIV?

• PrEP: Builds up sufficient drug levels in the blood and tissues before exposure to block any HIV that may enter the body.
• PEP: Inhibits HIV replication after potential exposure, before it can enter cells and multiply.

How to Get PrEP and PEP?

Using PrEP and PEP is not simply a matter of “getting the medication and taking it.” It requires a systematic process and should be under the care of a specialist physician for safety and optimal results.

What tests are required before taking the medication?

For PrEP, before starting, you must undergo health checks, especially for HIV and kidney function.

• HIV test to confirm you are not infected before starting.
• Kidney function test (Creatinine), as PrEP can affect kidney filtration.
• Hepatitis B and C tests.
• Tests for other sexually transmitted infections (e.g., syphilis, gonorrhea).

For PEP, it’s an emergency, so medication is often started immediately after risk assessment, followed by additional tests.

• Initial HIV test to confirm you are not currently infected.
• Basic blood tests and liver/kidney function tests.
• May include tests for other STIs as appropriate, such as hepatitis or syphilis.

If there’s a chance you “might already be infected with HIV,” do NOT use PrEP as it risks “drug resistance,” which is harder to treat.

Do I need to see a doctor first, or can I buy the medication myself?

PrEP and PEP are special controlled medications that should absolutely NOT be purchased for self-medication.

• Must be evaluated by a physician, undergo blood tests, and receive continuous follow-up.
• Especially PEP, which is a full course of antiretroviral drugs, must be closely monitored by a physician.

How to Take Care of Yourself After Receiving Medication?

After starting PrEP or PEP, it’s not just about “taking all the medication.” You also need to take care of yourself in various ways to ensure your body responds well to the medication and to reduce the chance of side effects.

What symptoms or side effects should I watch for?

Generally, PrEP and PEP are considered highly safe medications, approved by the World Health Organization (WHO) and the Food and Drug Administration (FDA) in Thailand and internationally. However, like all medications, some individuals may experience side effects.

PrEP: Symptoms commonly found in the first 1-2 weeks

• Mild nausea
• Fatigue or headache
• Bloating or diarrhea
• Loss of appetite

Generally, these symptoms will disappear on their own as the body adjusts and are not dangerous. However, in some (very rare) cases, effects on kidney function may be observed, for which the doctor will schedule regular blood tests to monitor. If symptoms are severe or do not resolve, you should consult a doctor.

PEP: Some people may experience more pronounced symptoms than with PrEP due to the combination of multiple drugs.

• Nausea, vomiting
• Abdominal pain or diarrhea
• Weakness, feeling tired
• Headache
• Rash (in some cases)

Taking the medication with food can help reduce nausea. If symptoms are severe or unusual, such as a rash, difficulty breathing, dark urine, or right-sided flank pain, you should seek immediate medical attention!

What foods or drinks should be avoided while on medication?

• Avoid alcohol or consume as little as possible to reduce the burden on the liver.
• Avoid medications that affect the liver/kidneys. If you need to use other medications concurrently, always inform your doctor first.
• Avoid foods or supplements whose safety is uncertain, especially herbal remedies or weight loss products.
• You should get enough rest, drink plenty of water, and observe any changes in your body.

What tests are required during medication use?

If using PrEP continuously:

• Repeat HIV testing every 3 months.
• Kidney function test every 6 months.

If using PEP:

• HIV test 4-6 weeks after completing the course.
• May have another repeat test at 3 months to confirm results.

Approximate Costs of PrEP and PEP

The cost of PrEP and PEP will depend on several factors, such as the brand used, the service provider (private clinic vs. public hospital), and your health insurance coverage.

PrEP Prices (Pre-exposure medication)

PrEP is typically prescribed as a “monthly medication” that needs to be taken daily and continuously. Doctors will schedule follow-up appointments every 3 months, which may involve minor additional blood test fees (e.g., ฿400 – ฿1,000 per visit).

PEP Prices (Post-exposure medication)

However, it is recommended to call clinics or hospitals in advance to inquire about price differences and whether they offer 24-hour emergency PEP services.

How Long Does It Take to Be Effective?

Both PrEP and PEP require time for the medication to take effect in the body before they can fully prevent HIV infection. This appropriate timeframe varies depending on the type of medication and the method of use.

PrEP does not provide immediate protection after starting. It takes time for the medication to accumulate in the body to a level that can effectively prevent infection. If medication is frequently missed or not taken on time, drug levels may drop, and efficacy may decrease.

After this period, if PrEP is used consistently every day, it can prevent HIV infection by up to >99%, according to reports from WHO and CDC.

PEP provides immediate protection after potential exposure to prevent the virus from establishing itself in the body.

• Must be started within 72 hours and taken for the full 28 days continuously. Do not miss a dose, as this can lead to drug resistance. If you miss a dose for more than 24 hours, you must consult your doctor immediately. Do not stop abruptly, even if side effects are annoying.
• While on medication, the body will try to stop HIV from multiplying if it has entered the system.

PEP does not prevent in advance like PrEP; instead, it “stops the virus that may be trying to enter cells,” making it a true race against time.

How Long Does the Efficacy of PrEP and PEP Last?

Many people think that once they use PrEP or PEP, they will be “safe forever.” However, both medications provide protection only while the medication is being used continuously or for the full course.

If I stop PrEP, does it still protect me?

No, it does not. PrEP only protects against HIV when there are sufficient drug levels in the body. If you stop taking the medication, drug levels will gradually decrease and disappear from the bloodstream within a few days.

After using PEP, am I still at risk?

Yes, you can still be at risk in the future if you engage in risky behaviors again. PEP does not provide immunity like a vaccine.

• After completing the 28-day course, you must repeat HIV testing within 4-6 weeks, and in some cases, another test at 3 months to confirm the results.
• If you experience new exposure after completing PEP (e.g., another instance of unprotected sex), you will need to re-evaluate the use of PEP or consider switching to PrEP instead.

How to Identify Genuine vs. Fake PrEP and PEP?

Where can I purchase the medication to ensure it’s genuine?

• Obtain medication from authorized hospitals or clinics, such as STI clinics, sexual health clinics, or public or private hospitals.
• Have a clear prescription from a doctor.
• Receive the medication in unopened packaging.

Avoid purchasing from sources that cannot confirm the manufacturing origin, such as Facebook pages, LINE, or unauthorized sellers. While the price might be lower, the risk is significantly higher.

What do fake medications look like?

• No FDA registration number or a fake number.
• Labels are unclear, text is blurry, or misspelled.
• Tablets are broken, faded in color, or do not match the expected appearance.
• No package insert or the label is in an unreadable language.
• Packaging appears old, deformed, or previously opened.

What are the dangers of fake medications?

• No actual active ingredients → Cannot prevent HIV at all.
• Use substandard ingredients → May cause liver, kidney, or neurological toxicity.
• Leads to drug resistance → If you do contract HIV, the medication will be harder to treat and carries a risk of death.

Summary: PrEP and PEP Prevent HIV, But Are Used in Different Situations

PrEP is a medication used before exposure to risk to prevent HIV infection. It is suitable for individuals with ongoing risk behaviors, such as having multiple sexual partners or being in an uncertain relationship.

PEP is a medication used after an emergency, such as forgetting protection, sexual assault, or accidental blood exposure. It must be started within 72 hours and taken for the full 28 days.

Both methods require medical supervision, have some side effects but are generally highly safe, and should be used continuously or for the full course to achieve the best results. You should absolutely NOT self-medicate.

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