Sustiva, with its active ingredient efavirenz, is a prescription medication primarily used in the treatment of HIV (Human Immunodeficiency Virus) infection. It belongs to a class of drugs known as non-nucleoside reverse transcriptase inhibitors (NNRTIs), which work by blocking the reverse transcriptase enzyme. This enzyme is crucial for the replication of the HIV virus, and its inhibition helps to prevent the virus from multiplying in the body. Sustiva is often used in combination with other antiretroviral medications as part of a highly active antiretroviral therapy (HAART) regimen to effectively manage HIV infection. It is important for patients to follow their healthcare provider's instructions closely when taking Sustiva, as adherence to the treatment plan is key to managing the virus and improving health outcomes.