Efavirenz is a drug used in the treatment of HIV, specifically HIV Type-1. The drug works by interacting with an enzyme known as reverse transcriptase, the enzyme needed to transcribe viral RNA into DNA. This, in the long-term, reduces the progression of the disease.The drug is usually not taken alone, but is instead typically given alongside two other anti-HIV drugs of the same class: tenofovir and emtricitabine. These three medicines can be taken in one tablet, known as Atripla, that makes it considerably easier for patients to stick to a given regimen. Efavirenz may cause serious psychiatric side-effects like depression.