Efavirenz (EFV), sold under the brand names Sustiva among others, is an antiretroviral medication used to treat and prevent HIV/AIDS.

[1] Common side effects include rash, nausea, headache, feeling tired, and trouble sleeping.

[7][8] 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[9] and children.

[14] People who have taken this medication before and experienced an allergic reaction should avoid taking further efavirenz dosages.

[17][18] Efavirenz may lengthen the QT interval so should not be used in people with or at risk of torsades de pointes.

Efavirenz will lower the blood levels of most protease inhibitors, including amprenavir, atazanavir, and indinavir.

Similar to the effect seen with protease inhibitors, efavirenz lowers the blood levels of antifungal drugs like voriconazole, itraconazole, ketoconazole, and posaconazole.

Efavirenz is not effective against HIV-2, as the pocket of the HIV-2 reverse transcriptase has a different structure, which confers intrinsic resistance to the NNRTI class.

[5] The shorter half-life with chronic administration may be due to induction of cytochrome P450 enzymes by efavirenz.

[7][8] In late 2018, Thailand's Government Pharmaceutical Organization (GPO) announced that it will produce efavirenz after receiving WHO approval.

[34] In Thailand, a one-month supply of efavirenz + Truvada, as of June 2012, cost 2,900 baht (US$90), and there is a social program for patients who cannot afford the medication.

Its Government Pharmaceutical Organization product costs 180 baht per bottle of thirty 600 mg tablets.

GPO will devote 2.5 percent of its manufacturing capacity to make 42 million efavirenz pills in 2018, allowing it to serve export markets as well as domestic.

[35] Abuse of efavirenz by crushing and smoking the tablets for supposed hallucinogenic and dissociative effects has been reported in South Africa, where it is used in a mixture known as whoonga and nyaope.

"[26] As of 2016, efavirenz is marketed in various jurisdictions under the brand names Adiva, Avifanz, Efamat, Efatec, Efavir, Efavirenz, Efcure, Eferven, Efrin, Erige, Estiva, Evirenz, Filginase, Stocrin, Sulfina V, Sustiva, Virorrever, and Zuletel.

[40] As of 2016, the combination of efavirenz, tenofovir, and emtricitabine is marketed in various jurisdictions under the brand names Atripla, Atroiza, Citenvir, Oditec, Teevir, Trustiva, Viraday, and Vonavir.