Post-exposure prophylaxis (PEP) is a way of preventing HIV infection. It involves using a four-week course of the same drugs used to treat HIV, which you take very soon after you may have been exposed to the HIV virus.
Each course of PEP contains three anti-HIV drugs. It is important to take all three drugs for PEP to be effective.
Two of these medications are usually from a class of drugs known as nucleoside reverse transcriptase inhibitors (NRTIs). This is often tenofovir (tenofovir disoproxil or tenofovir alafenamide) and emtricitabine. These two medications are often taken together in a single pill.
A third medication, usually from the integrase inhibitor class, may be taken separately. Often this will be raltegravir or dolutegravir. If the third medication is bictegravir, then all three drugs are combined in one pill.
Sometimes a protease inhibitor is used instead of an integrase inhibitor, such as darunavir or atazanavir.
In the UK, the recommended PEP regimen is tenofovir disoproxil, emtricitabine, and raltegravir once a day for at least 28 days.
The drugs used in PEP today are less likely to cause side effects than in the past. They also have fewer potential drug-drug interactions.
Another type of drug called a ‘boosted protease inhibitor’ may also be used if an integrase inhibitor isn’t right for you (for example, if you have certain health conditions).
Boosted protease inhibitors consist of one main protease inhibitor taken with a small amount of another protease inhibitor called ritonavir. This low dose of ritonavir ‘boosts’ and maintains levels of the main protease inhibitor in your body.
Boosted protease inhibitors that may be prescribed include lopinavir, darunavir, or atazanavir.
Drug-drug interactions are more likely with protease inhibitors. There is more information about drug-drug interactions further down the page.
Many people will take PEP without having any side effects. However, all medication can cause side effects. On this page we talk about common side effects of the drugs used in PEP. Common side effects are ones that happen to more than 1 in 100 people.
However, just because symptoms are common, it doesn’t mean you have to put up with them. If side effects are making it hard for you to take your medication, you should speak to your doctor. It’s really important that you finish the whole course.
It’s also important to know that most of the information we have about side effects come from HIV-positive people taking the same medications over many years as HIV treatment.
Some common side effects haven't been included as they are not likely to happen in a month.
There are some side effects that are common for all types of PEP medication listed below. These are:
On this page, other common side effects are listed for each drug. The most common medicines and their side effects are listed first, with less common medicines listed further down the page.
Human immunodeficiency virus, the virus which causes AIDS. There are two variants: HIV-1, and HIV-2. HIV-1 is by far the most common worldwide. See ‘subtype’ for more information.
Abbreviation of a Latin term meaning every night.
An enzyme that HIV uses to break up large proteins into smaller ones from which new HIV particles can be made.
A level of viral load that is too low to be picked up by the particular viral load test being used or below an agreed threshold (such as 50 copies/ml or 200 copies/ml). An undetectable viral load is the first goal of antiretroviral therapy.
Measurement of the amount of virus in a blood sample, reported as number of HIV RNA copies per milliliter of blood plasma. Viral load is an important indicator of HIV progression and of how well treatment is working.
Common side effects of bictegravir include:
For more information, read our factsheet on bictegravir.
Common side effects of dolutegravir include:
Rarely, dolutegravir can cause a hypersensitivity (allergic) reaction. If you develop a rash with other symptoms, such as a fever, seek medical advice.
For more information, read our factsheet on dolutegravir.
Common side effects of emtricitabine with tenofovir are:
There are two types of tenofovir. Tenofovir disoproxil (found in Truvada) can affect the kidneys, so you might be given tenofovir alafenamide (found in Descovy) if you already have severe kidney disease.
For more information, read our factsheets on Truvada and Descovy.
Common side effects of lamivudine include:
For more information, read our factsheet on lamivudine.
Common side effects of raltegravir include:
Rarely, raltegravir can cause a hypersensitivity (allergic) reaction. If you develop a rash with other symptoms, such as a fever, seek medical advice.
For more information, read our factsheet on raltegravir.
There have been occasional reports of muscle-related side effects from people taking the combination of emtricitabine/tenofovir and raltegravir.
These included reports of myalgia (muscle pain), and rhabdomyolysis (muscle damage that can lead to renal complications). If you have a history of these conditions, or you are using other medications associated with these conditions (such as statins), you might be monitored more closely or offered an alternative drug.
These medicines might be prescribed to you if you’re unable to take more common PEP combinations.
Common side effects of atazanavir include:
Yellowing skin or eyes is fairly common when taking atazanavir, especially when you first start the drug. Although this can look scary, it is harmless and does not mean that your liver is damaged or not working in any way.
Rarely, atazanavir can cause a hypersensitivity (allergic) reaction. If you develop a rash with other symptoms, such as a fever, seek medical advice.
For more information, read our factsheet on atazanavir.
Common side effects of darunavir include:
For more information, read our factsheet on darunavir.
For more information, read our factsheets on Stribild and Genvoya.
Lopinavir (200mg) and ritonavir (50mg), taken twice daily, often causes diarrhoea and other gastrointestinal issues.
Other common side effects of lopinavir with ritonavir are:
For more information, read our factsheet on lopinavir/ritonavir.
Side effects usually appear soon after starting PEP as the body adjusts to the new medications. Side effects often decrease, become manageable, or go away completely after a few days or weeks.
It depends. PEP can cause drug interactions with other medications. A drug interaction is when one medicine affects how another medicine works. For example, taken together, one medicine may increase the side effects of another medicine.
For example, antacids, multivitamins, and iron supplements should be avoided if you’re taking raltegravir.
It is important to tell your doctor or pharmacist about all other medicines and drugs that you are taking. This includes those prescribed by another doctor, over-the-counter medicines (including inhalers and nasal sprays), supplements, herbal and alternative treatments, and recreational drugs.
With all PEP regimens, your doctor or pharmacist should check for drug-drug interactions.
The University of Liverpool provides an online tool to check for interactions between anti-HIV drugs, other medications and recreational drugs. You enter the names of the medication you are taking and the results are provided with a traffic-light system: if the result is red or orange, it’s worth checking with your doctor or pharmacist. If it’s green, there shouldn’t be any problem. Visit www.hiv-druginteractions.org/checker.
