Efavirenz (EFV), sold under the brand names Sustiva among others, is an antiretroviral medication used to treat and prevent HIV/AIDS. It is generally recommended for use with other antiretrovirals. It may be used for prevention after a needlestick injury or other potential exposure. It is sold both by itself and in combination as efavirenz/emtricitabine/tenofovir. It is taken by mouth. Common side effects include rash, nausea, headache, feeling tired, and trouble sleeping. Some of the rashes may be serious such as Stevens–Johnson syndrome. Other serious side effects include depression, thoughts of suicide, liver problems, and seizures. It is not safe for use during pregnancy. It is a non-nucleoside reverse transcriptase inhibitor (NNRTI) and works by blocking the function of reverse transcriptase. Efavirenz was approved for medical use in the United States in 1998, and in the European Union in 1999. It is on the World Health Organization's List of Essential Medicines. As of 2016, it is available as a generic medication. Medical uses For HIV infection that has not previously been treated, the United States Department of Health and Human Services Panel on Antiretroviral Guidelines recommends the use of efavirenz in combination with tenofovir/emtricitabine (Truvada) as one of the preferred NNRTI-based regimens in adults and adolescents and children. Efavirenz is also used in combination with other antiretroviral agents as part of an expanded post-exposure prophylaxis regimen to reduce the risk of HIV infection in people exposed to a significant risk (e.g. needlestick injuries, certain types of unprotected sex, etc.). Pregnancy and breastfeeding Efavirenz is safe to use during the first trimester of pregnancy. Efavirenz passes into breast milk and breast-fed infants may be exposed to efavirenz. Contraindications People who have taken this medication before and experienced an allergic reaction should avoid taking further efavirenz dosages. Hypersensitivity reactions include Stevens–Johnson syndrome, toxic skin eruptions, and erythema multiforme. Adverse effects Neuropsychiatric effects are the most common adverse effects, and include disturbed sleep (including nightmares, insomnia, disrupted sleep, and daytime fatigue), dizziness, headaches, vertigo, blurred vision, anxiety, and cognitive impairment (including fatigue, confusion, and memory and concentration problems), and depression, including suicidal thinking. Some people experience euphoria. Rash and nausea may occur. Use of efavirenz can produce a false positive result in some urine tests for marijuana. Efavirenz may lengthen the QT interval so should not be used in people with or at risk of torsades de pointes. Efavirenz may cause convulsions in adult