The two medicines in PrEP, tenofovir and emtricitabine, also act against the hepatitis B virus. That's why everyone is tested for hepatitis B before starting: your result decides whether on-demand PrEP is an option and how PrEP must be stopped. Most people can still take PrEP whatever their result, but the plan changes.
This guide explains your hepatitis B results in plain words, what each one means for PrEP, and how to stop safely if you have the virus.
Why hepatitis B changes how PrEP works
Hepatitis B is a virus that infects the liver. In many adults it clears on its own, but in some it stays long-term, often without symptoms. It is common in parts of Asia, including Thailand, and it spreads through blood and sex.
When someone with hepatitis B takes PrEP, the medicines keep the virus quiet. If they then stop suddenly, the virus can bounce back fast. This is called a flare, and it can inflame the liver, sometimes seriously.
That single fact explains the main hepatitis B rules for PrEP:
- On-demand 2-1-1 PrEP is not suitable. Stopping and starting around sex creates repeated on-off cycles.
- Daily PrEP is usually still possible, with extra liver monitoring.
- Stopping is always planned with a doctor, never done suddenly.
You can read how the start-up checks fit together in our guide to tests before starting PrEP.
Your hepatitis B results, decoded
A hepatitis B screen usually looks at three markers. The Hepatitis B Foundation's guide to blood tests explains that all three results together are needed to understand someone's status.
- Surface antigen (HBsAg): part of the virus itself. Positive means hepatitis B is in your body now.
- Surface antibody (anti-HBs): protection. Positive means you are immune, from a vaccine or from clearing a past infection.
- Core antibody (anti-HBc): a marker of past or current infection. Vaccines don't cause it, so it shows you have met the real virus at some point.
Common result patterns and what they mean for PrEP
| Surface antigen | Surface antibody | Core antibody | What it usually means |
|---|---|---|---|
| Negative | Negative | Negative | Not immune; vaccination advised |
| Negative | Positive | Negative | Immune from vaccination |
| Negative | Positive | Positive | Immune after a past infection |
| Positive | Negative | Positive | Living with hepatitis B now |
| Negative | Negative | Positive | Unclear; needs a doctor's review |
If your report shows a number for surface antibody, a result below about 10 is usually treated as not protected. A doctor will assess your situation and explain your own pattern.
The last row, a positive core antibody on its own, is the one that confuses people most. It can mean an old infection where protection has faded, or occasionally a hidden infection, so further tests may be needed before deciding on 2-1-1.
Three situations and what each means for PrEP
Once your results are back, most people fall into one of three groups.
You are immune
This is the simplest case. You can choose daily or on-demand PrEP, and hepatitis B doesn't affect how you stop. Our guide to on-demand 2-1-1 PrEP explains whether that schedule suits you.
You are not immune
You don't have hepatitis B, but you could catch it. Vaccination is strongly advised and usually involves a short course of injections over several months.
Not being immune doesn't rule out either PrEP schedule: the 2-1-1 restriction applies to people who have hepatitis B. Hepatitis B can be passed on during sex, so you may be rechecked at follow-up until the vaccine has worked.
You are living with hepatitis B
PrEP is often still possible, but only as daily PrEP. You'll usually need extra tests, such as liver function and a measure of how much virus is in the blood, and referral to a liver specialist.
For some people, the same medicines also become part of their hepatitis B care. This is a decision for a doctor, not something to plan alone.
Does PrEP protect against hepatitis B?
PrEP medicines are active against hepatitis B, but PrEP is not an approved way to prevent it. Protection would also disappear the moment you stop or miss pills.
The reliable protection against hepatitis B is vaccination. Condoms also lower the risk.
HIV and hepatitis B together
HIV and hepatitis B spread in similar ways, which is why PrEP care checks for both. If a PrEP user ever tests positive for HIV, their hepatitis B result also shapes which HIV treatment a doctor chooses. Knowing both results early keeps future options simple. PrEP doesn't prevent other STIs either, as our guide to PrEP and STIs explains.
Stopping PrEP safely if you have hepatitis B
If you have hepatitis B, stopping PrEP is a medical decision. Here is what a safe plan usually looks like:
- Talk to a doctor before your last pill, even if you only want a short break.
- Agree whether to stop at all. Some people continue the same medicines to keep hepatitis B controlled.
- Have liver tests after stopping, often for several months.
- Know the warning signs: yellow skin or eyes, dark urine, pale stools, tummy pain or feeling very unwell all need prompt medical care.
Running out of pills by accident counts as stopping, so plan refills early. Our guide to PrEP refills in Pattaya helps you avoid gaps, and our advice on what to do after a missed PrEP dose covers the occasional slip.
Monitoring over time
Everyone on PrEP returns about every three months for an HIV test, and our guide to HIV testing in Pattaya explains how that works. Kidney checks continue too, as covered in our guide to PrEP and your kidneys.
If you have hepatitis B, liver tests are added to that routine. If you weren't immune at the start, a doctor may repeat the hepatitis B screen until vaccination is complete.
PrEP and hepatitis B in Pattaya
Many visitors and expats don't know their hepatitis B status, especially if they were vaccinated as children and have no records. A test at your first PrEP visit answers that question. Our page on getting PrEP in Pattaya walks through each step.
Hepatitis B vaccination is widely available in Thailand. If you're not immune, ask us for advice on where to get it, and check PrEP prices before you book.
Frequently asked questions
Can you take PrEP if you have hepatitis B?
Often yes, but only as daily PrEP with extra liver monitoring. On-demand 2-1-1 is not suitable, and stopping must be planned with a doctor.
Does PrEP prevent hepatitis B?
The medicines are active against hepatitis B, but PrEP is not a reliable way to prevent it. Vaccination is the proper protection.
What does a low hepatitis B surface antibody mean?
It usually means you are not protected, either because you were never vaccinated or immunity has faded. A doctor may suggest a vaccine course or a booster.
Why is 2-1-1 PrEP not allowed with hepatitis B?
Taking PrEP only around sex means repeatedly starting and stopping. With hepatitis B, each stop can trigger a flare of liver inflammation.
Do I need a hepatitis B test if I was vaccinated?
Yes, because records are often missing and immunity can fade. The test confirms your status and shapes your PrEP plan.
Not sure of your hepatitis B status? Message us on LINE or WhatsApp and we'll explain how testing fits into starting PrEP.