Efavirenz (brand names Sustiva and Stocrin) is a non-nucleoside reverse transcriptase inhibitor (NNRTI) and is used as part of highly active antiretroviral therapy (HAART) for the treatment of a human immunodeficiency virus (HIV) type 1.

For HIV infection that has not previously been treated, efavirenz and lamivudine in combination with zidovudine or tenofovir is the preferred NNRTI-based regimen.

Efavirenz is also used in combination with other antiretroviral agents as part of an expanded postexposure prophylaxis regimen to prevent HIV transmission for those exposed to materials associated with a high risk for HIV transmission.

The usual adult dose is 600 mg once a day taken on an empty stomach at bedtime.

Efavirenz was combined with the popular HIV medication Truvada and approved by the FDA in July of 2006, under the brand name Atripla. This was done to simplify the drug regimen for the many patients who take these two medications in combination.