Key points
- This is one type of oral PrEP – a tablet taken to prevent HIV infection.
- It’s often known by its brand name, Descovy.
- This page provides detailed information about how to start and stop PrEP, required tests and checkups, side effects, drug interactions and drug resistance.
- Other types of PrEP are also available.
What is PrEP?
PrEP stand for pre-exposure prophylaxis. This means preventing HIV by taking anti-HIV drugs.
PrEP allows you to have the sex you want without the fear of contracting HIV.
How does it work?
The anti-HIV drugs in PrEP stop HIV from entering your cells. You need to take PrEP every day to make sure that the drugs maintain high levels in your bloodstream to prevent HIV infection.
What is tenofovir alafenamide / emtricitabine?
This is a tablet which contains two anti-HIV drugs, tenofovir alafenamide / emtricitabine. It is an alternative to tenofovir disoproxil / emtricitabine (Truvada), which is the most commonly used form of PrEP. Tenofovir alafenamide works in a similar way to tenofovir disoproxil, but is less likely to cause bone or kidney problems. The brand name of tenofovir alafenamide / emtricitabine is Descovy.
The same tablet can also be used by people living with HIV as part of their treatment, in combination with another medication. This is different from PrEP. There’s more information about this on another page.
What other types of PrEP are there?
Tenofovir disoproxil / emtricitabine is the most widely used PrEP tablet. It works well for most people. There’s more information about this on another page.
Different PrEP drugs can also be taken as an injection or in a vaginal ring, but these are not available in all countries.
What’s the difference between PrEP and PEP?
You start to take pre-exposure prophylaxis (PrEP) before you are exposed to HIV and continue to take it for as long as you need it, to protect against infection. You take post-exposure prophylaxis (PEP) after you have been exposed to HIV, for a fixed period of one month.
Effectiveness
Most PrEP studies have been of tenofovir disoproxil / emtricitabine, the most widely used PrEP tablet. However, a large study in gay and bisexual men showed that PrEP consisting of tenofovir alafenamide and emtricitabine was just as effective in preventing HIV as PrEP consisting of tenofovir disoproxil and emtricitabine. The only study to test tenofovir alafenamide / emtricitabine as PrEP for women (PURPOSE 1) will report its results later in 2024.
Is this type of PrEP available to me?
Tenofovir alafenamide / emtricitabine is approved for use as PrEP in Argentina, Australia, Canada, China, Kenya, Mexico, New Zealand, Taiwan, Thailand, United Arab Emirates, United States and Uruguay. It is not currently approved for PrEP use in the European Union or other countries.
You can check the PrEPWatch website to see if tenofovir alafenamide / emtricitabine has been approved for use in your country since this page was written (July 2024).
It is not usually available to cisgender women and others who need protection during receptive vaginal sex. So far, research on how well tenofovir alafenamide / emtricitabine works has only been completed with gay and bisexual men and transgender women.
In most countries, this type of PrEP is only available as branded Descovy, which is more expensive than the most widely used PrEP pill, tenofovir disoproxil / emtricitabine. For this reason, its use may be restricted to individuals who have a clinical reason to need this specific type of PrEP. For example, in the UK, tenofovir alafenamide / emtricitabine is only approved for use as PrEP by people with reduced kidney function or osteoporosis (reduced bone density) and for adolescents during the critical period of bone growth.
Services which provide HIV testing, treatment for sexually transmitted infections or treatment for HIV may also provide PrEP – or have information on local services which do.
Tests before starting PrEP
Before starting PrEP, you need to have an HIV antibody / antigen test to check that you don’t have HIV already. If you have HIV, taking PrEP will lead to your HIV developing resistance to the drugs in PrEP. As this would mean that these drugs would not work properly as HIV treatment, it’s important to avoid this.
It’s usually recommended to have a blood test for kidney function. In high-income countries, all PrEP users should have this test. In some low and middle income countries, it may only be available to people over the age of 30 – this is because kidney problems are unusual in younger people.
For people with mild or moderate kidney damage, this type of PrEP (which includes tenofovir alafenamide) is safer than PrEP that includes tenofovir disoproxil. Nonetheless, a very small proportion of people are unable to take tenofovir alafenamide because they have seriously weakened kidney function (creatine clearance below 30 mL/min).
You will also be tested for hepatitis B. Tenofovir is active against hepatitis B virus, so it is important to know how to take PrEP safely if you have hepatitis B (see below).
How to take PrEP
For PrEP to work, it needs to be taken correctly. This means having enough PrEP in your body at the times when you need protection.
PrEP can be taken for short or long periods of time, depending on the sex you are having, how comfortable you are with PrEP and what helps you avoid missing doses. As a PrEP user, you need to know how to start taking it, how to stop and how to restart it. You also need to know what to do if you realise you have missed a dose.
Our advice on stopping and starting tenofovir alafenamide / emtricitabine PrEP is based on guidance from the US Centers for Disease Control and Prevention (CDC) and other public health agencies. They recommend taking this form of PrEP on an ongoing, daily basis. Some experts believe that this form of PrEP can also be taken more flexibly, in the same way as we outline on our page on tenofovir disoproxil / emtricitabine. However, at the time of writing, no published guidelines recommend this more flexible approach for tenofovir alafenamide / emtricitabine, so the advice on this page is more conservative.
Starting PrEP
If you are taking tenofovir alafenamide and emtricitabine as PrEP, you take one tablet a day. Start taking it seven days before you have condomless sex to make sure the medication reaches adequate levels in your bloodstream. If you are likely to have sex within the first seven days after starting PrEP, take two tablets at least two hours before having sex and then take PrEP every day.
Take the pill at around the same time each day (give or take two hours). It may be easier to get into the habit of taking PrEP if you combine it with a daily routine. This could be brushing your teeth, having dinner or going to bed. Think about where you will keep your pills – somewhere you will see them at the right time, or kept out of the sight of other people? You could set an alarm on your phone or watch each day. Or you could get a pill box from a pharmacy – this makes it easy to see whether you have taken or missed a dose.
If you forget to take a dose, you can take it within 12 hours. If you remember later than 12 hours after the time you normally take PrEP, take the next dose at the normal time. You need to take at least four doses a week to protect against HIV.
Stopping PrEP
It’s fine to take a break from PrEP if you won’t need protection from HIV for a while.
Before you stop, continue to take PrEP once a day for seven days after the last time you had sex without a condom. For example, if you last had sex without a condom on Sunday, take PrEP for another week, and then stop.
Checkups while taking PrEP
Regular checkups are important while taking PrEP.
You should have an HIV test every three months, to check that you remain HIV negative. You may be offered an extra test one month after starting PrEP, to check that you didn’t acquire HIV just before starting PrEP. It is best to be tested for HIV using a fourth-generation antibody-antigen test. These are more sensitive than rapid antibody tests and will detect HIV sooner. The majority of people who acquire HIV will receive a positive result using a fourth-generation HIV test within four weeks of exposure.
Rapid HIV tests which use a sample of moisture from the mouth do not always pick up recent infections, so should not be relied on while using PrEP. In some situations, you might be offered a viral load test: this is able to pick up very recent infections, but the test not available everywhere.
You may also have regular blood tests to check how PrEP is affecting your kidney function, especially if you are over 40 or 50 years old, or have slightly reduced kidney function. You may also have tests for other sexually transmitted infections at these clinic visits.
If you stop taking PrEP and subsequently have condomless sex more than a week later, it’s a good idea to get a fourth-generation antibody test before starting PrEP again.
If you are not taking PrEP and you have flu-like symptoms, possibly with a rash, within a month of condomless sex, this may be a symptom of HIV infection. You should have a fourth-generation HIV test a month after the most recent exposure and delay starting or re-starting PrEP until you have been confirmed HIV negative.
If you have just started PrEP and you have flu-like symptoms, possibly with a rash, this may be a symptom of HIV infection. Contact your clinic immediately to arrange a fourth-generation HIV test and/or viral load test. Your clinic may add a third drug to your PrEP in case you have HIV.
Telling your GP you are taking PrEP
It is a good idea to tell your general practitioner or primary care physician that you are taking PrEP containing tenofovir alafenamide and emtricitabine, to avoid interactions with other prescription medicines.
PrEP if you have hepatitis B
Tenofovir alafenamide, one of the drugs in PrEP, is also used to treat hepatitis B. You will be tested for hepatitis B before you start PrEP. If you have hepatitis B, you must take PrEP every day – you should not start and stop PrEP just for the times you need protection.
If you want to take a break from PrEP, you should discuss with your clinic how to safely stop taking it. Stopping tenofovir alafenamide suddenly when you have hepatitis B could lead to a flare-up of hepatitis.
Who shouldn’t take PrEP?
- People living with HIV
- People with seriously reduced kidney function (for example, creatine clearance below 30 mL/min). Your kidney function should be tested before starting PrEP.
- Adolescents weighing less than 35kg (five and a half stone)
Side effects
The most common side effects of PrEP containing tenofovir alafenamide and emtricitabine (affecting at least one in ten people) are:
- Nausea (feeling sick, being sick)
Common side-effects affecting at least one in a hundred people are:
- Diarrhoea
- Headache
- Stomach pain, flatulence
- Tiredness, abnormal dreams
- Rash
Taking tenofovir alafenamide may lead to increased creatinine levels in fewer than one in a hundred people. High creatinine levels can be a sign of abnormal kidney function. Your blood will be tested every year to check your kidney function and creatinine levels, and more frequently if you are over 40 or your kidney function is slightly below normal.
Taking tenofovir alafenamide as PrEP may lead to modest increases in weight, blood pressure, cholesterol and fats called triglycerides.
Taking PrEP with food or just after a meal may limit any side effects.
Side effects are most likely to occur during the first month you are taking PrEP. If you have side effects which don’t go away or get worse, speak to staff at your clinic.
Interactions with other medicines
When two drugs are taken at the same time, their interaction can affect the drugs’ effectiveness and side effects.
Taking tenofovir alafenamide at the same time as high-dose aciclovir, cidofovir, ganciclovir, valaciclovir, valganciclovir or gentamicin may increase the risk kidney damage.
Some anticonvulsant drugs or antibiotics used to treat tuberculosis may reduce levels of tenofovir alafenamide in your body. Discuss with your doctor whether it is safe to continue PrEP when taking these medicines.
PrEP containing tenofovir alafenamide and emtricitabine can interact with high doses of non-steroidal anti-inflammatory drugs (NSAIDS) such as ibuprofen or diclofenac – these medications are taken for pain or inflammation. Discuss with your doctor whether it is safe to take both PrEP and NSAIDS.
PrEP does not interact with:
- Alcohol or recreational drugs
- Hormonal contraception
- Gender-affirming hormone therapy
- Erectile dysfunction drugs
- Anabolic steroids
Tell your clinic if you use protein or creatine powders. These can impact the results of blood tests that check your kidney health.
The University of Liverpool provides an online tool to check for interactions between anti-HIV drugs (including PrEP) and other medications. You enter the names of your PrEP drugs (tenofovir alafenamide and emtricitabine) in the left column, and the other medications you are taking in the next column. The results are provided with a traffic-light system: if the result is red or amber, 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 or download the Liverpool HIV iChart app for iPhone or Android.
Drug resistance
Some people worry that while taking PrEP they may get drug resistant HIV. It’s important to remember that HIV drug resistance can only happen if you take PrEP when you already have HIV. This is why you should get tested for HIV before you start PrEP, and keep testing regularly.
If you continue taking PrEP or start taking PrEP again after you acquire HIV, this could drive HIV to develop resistance to the drugs you are taking as PrEP. This would restrict your options for treating HIV.
But if you don’t have HIV and you take PrEP as directed, you almost certainly won’t catch HIV and you won’t develop drug resistance.
There is another way in which resistance can affect PrEP. There are a very small number of people who have acquired HIV when taking PrEP despite having adequate drug levels in their blood. In almost all cases, they acquired a form of HIV that had resistance to one of the drugs in PrEP. Resistance to both drugs in PrEP is highly unusual.
There’s more information about resistance on another page.
Does PrEP prevent STIs?
PrEP does not prevent other sexually transmitted infections so it’s a good idea to have regular tests for sexually transmitted infections while you are taking PrEP.