Efavirenz is a medication used to treat HIV. It was originally marketed under the brand name Sustiva, but generic versions are also available. It is taken in combination with other antiretroviral drugs.

The usual adult dose of efavirenz is one 600mg tablet per day.

Efavirenz is also available in a combination tablet with emtricitabine and tenofovir disoproxil (Atripla).

Efavirenz is from a class of drugs known as non-nucleoside reverse transcriptase inhibitors (NNRTIs). Your doctor will prescribe efavirenz as part of your HIV treatment, along with antiretrovirals from another class of drugs. It is important to take all the drugs as prescribed, every day. Each drug class works against HIV in a different way.

The aim of HIV treatment is to reduce the level of HIV in your body (viral load). Ideally, your viral load should become so low that it is undetectable – usually less than 50 copies of virus per ml of blood. Taking HIV treatment and having an undetectable viral load protects your immune system and stops HIV being passed on to someone else during sex.

It is recommended that you take efavirenz on an empty stomach. Some people find taking it with some food reduces side-effects, but you should avoid taking it with a high-fat meal; this may increase absorption of the drug, potentially increasing side-effects.

You should swallow the tablet whole, with some water. Don’t drink grapefruit juice with efavirenz as it can affect the level of the drug in your body.

HIV treatment works best if you take it every day. When would be a good time for you to plan to take your treatment? Think about your daily routine and when you will find it easiest to take your treatment. If you find efavirenz causes confusion or dizziness, taking it before you go to bed may help.

If you forget to take a dose of efavirenz, take it as soon as you remember. If it is almost time for your next dose, then don’t take a double dose, just skip the dose you’ve forgotten and carry on.

If you regularly forget to take your treatment, or you aren’t taking it for another reason, it’s important to talk to your doctor about this.

All drugs have possible side-effects. It’s a good idea to talk to your doctor about possible side-effects before you start taking a drug. If you experience something that might be a side-effect, talk to your doctor about what can be done. A full list of side-effects, including less common side-effects, should be included in the leaflet that comes in the packaging with efavirenz. If you have any questions, talk to your doctor or pharmacist.

We generally divide side-effects into two types:

Common – a side-effect that occurs in at least one in a hundred people (more than 1%) who take this drug.

Rare – a side-effect that occurs in fewer than one in a hundred people (less than 1%) who take this drug.

The most common side-effects of efavirenz are (most common in bold):

Rash, itching, abnormal dreams, difficulty concentrating, dizziness, headache, difficulty sleeping, drowsiness, abdominal pain, diarrhoea, nausea, vomiting, tiredness, anxiety, depression, raised triglyceride and liver enzyme levels.

Mood and sleep problems are most commonly experienced during the first four weeks of treatment and include feeling ‘out of sorts’, confusion, impaired concentration, sleep disturbance, abnormal dreams, anxiety and depression. In most cases these side-effects go away by themselves and it isn’t necessary to stop taking efavirenz. However, some people find them intolerable and need to change treatment as a result. If you have mental health problems, or have had in the past, efavirenz may not be a good choice for you. Talk to your doctor about other treatment options.

You should always tell your doctor and pharmacist about any other drugs or medication you are taking. That includes anything prescribed by another doctor, medicines you have bought from a high-street chemist, herbal and alternative treatments, and recreational or party drugs (‘chems’).

Some medicines or drugs are not safe if taken together – the interaction could cause increased, dangerous levels, or it could stop one or both of the drugs from working. Other drug interactions are less dangerous but still need to be taken seriously. If levels of one drug are affected, you may need to change the dose you take. This must only be done on the advice of your HIV doctor.

A list of drugs, known to have interactions with efavirenz,should be included in the leaflet that comes in the packaging with efavirenz. Tell your doctor if you are taking any of these drugs, and other drugs that are not on the list.

You should not take efavirenz with:

• astemizole
• bepridil
• cisapride
• dihydroergotamine
• ergonovine
• ergotamine
• methylergonovine
• midazolam
• pimozide
• St John's wort
• terfenadine
• triazolam.

Some drugs can interact with efavirenz and change blood levels of one or both drugs, so dose adjustments may be needed. This is the case for the anti-HIV drugs darunavir, fosamprenavir, lopinavir/ritonavir, ritonavir, ritonavir-boosted atazanavir, and maraviroc. It is also the case for other drugs including:

• acenocoumarol
• artemether/lumefantrine
• atorvastatin
• atovaquone/proguanil
• bupropion
• carbamazepine
• clarithromycin
• cyclosporine
• diltiazem
• ginkgo biloba
• itraconazole
• methadone
• phenobarbital
• phenytoin
• posaconazole
• pravastatin
• rifabutin
• rifampicin
• sertraline
• simeprevir
• simvastatin
• sirolimus
• tacrolimus
• voriconazole
• warfarin.

Efavirenz may reduce the effectiveness of some hormonal contraceptives (such as the pill, patches or an implant). If you are using this type of contraceptive to prevent pregnancy you should talk to your doctor about using an additional or different type of contraception.

If you are considering having a baby, or think you might be pregnant, talk to your doctor as soon as possible about which combination of anti-HIV medications would be right for you. It is important to take antiretroviral treatment during pregnancy to prevent passing HIV from mother to baby.

Efavirenz’s manufacturer does not recommend using the drug during pregnancy. 

However, many women have taken efavirenz while pregnant without any problems. The British HIV Association (BHIVA) recommends that women who are already taking anti-HIV medications and become pregnant can usually continue to take the same medication throughout their pregnancy. In addition, BHIVA lists efavirenz (in combination with other medications) as an option that may be recommended for women who start HIV treatment in pregnancy, depending on their individual circumstances.

Efavirenz is approved for use in children aged 3 months and over.

If you have any concerns about your treatment or other aspects of your health, it’s important to talk to your doctor about them.

For example, if you have a symptom or side-effect or if you are having problems taking your treatment every day, it’s important that your doctor knows about this. If you are taking any other medication or recreational drugs, or if you have another medical condition, this is also important for your doctor to know about.

Building a relationship with a doctor may take time. You may feel very comfortable talking to your doctor, but some people find it more difficult, particularly when talking about sex, mental health, or symptoms they find embarrassing. It’s also easy to forget things you wanted to talk about.

Preparing for an appointment can be very helpful. Take some time to think about what you are going to say. You might find it helpful to talk to someone else first, or to make some notes and bring them to your appointment. Our online tool Talking points may help you to prepare for your next appointment – visit www.aidsmap.com/talking-points 

For detailed information on this drug, visit the efavirenz pages in the A-Z of antiretroviral drugs.