Efavirenz (Sustiva) is an anti-HIV drug, which reduces the amount of virus in the body. Anti-HIV drugs such as efavirenz slow down damage to the immune system and prevent the occurrence of AIDS-defining illnesses.

Efavirenz is a non-nucleoside reverse transcriptase inhibitor (NNRTI). These drugs act by inhibiting HIV’s reverse transcriptase enzyme, but in a different way from the nucleoside reverse transcriptase inhibitors (NRTIs).

Efavirenz, formerly known by the codename DMP 266, was developed by Du Pont Pharma. It was approved for HIV treatment in the United States in 1998, and the European licence was granted in May 1999.

Efavirenz is marketed by Bristol-Myers Squibb under the trade name Sustiva in the United Kingdom, Ireland, France, Germany, Italy and Spain. The trade name Stocrin is used by Merck Sharp & Dohme, who market the drug in other European countries, Australia, Brazil, Latin America, South Africa and other regions. Generic versions are manufactured in India as Efavir (made by Cipla), Estiva (Genixpharma), Viranz (Aurobindo) and Efferven (Ranbaxy).

In the United States, efavirenz is also available in a triple-drug combination tablet called Atripla. This tablet, which is the first once-daily tablet containing a complete anti-HIV treatment regimen, contains 600mg efavirenz, 200mg FTC (emtricitabine) and 300mg tenofovir. It was approved in the United States in July 2006, but a European approval is not expected until the end of 2006.