A synthetic non-nucleoside reverse transcriptase (RT) inhibitor with antiviral activity. Efavirenz binds directly to the human immunodeficiency virus type 1 (HIV-1) RT, an RNA-dependent DNA polymerase, blocking its function in viral DNA replication. In combination with other antiretroviral drugs, this agent has been shown to significantly reduce HIV viral load, retarding or preventing damage to the immune system and reducing the risk of developing AIDS. Efavirenz induces activity of the cytochrome P450 system, accelerating its own metabolism. or A drug used with other drugs to treat infection with the human immunodeficiency virus (HIV). It blocks HIV from making copies of itself. It is a type of non-nucleoside reverse transcriptase inhibitor and a type of antiviral agent. Also called Sustiva.