Description: Cobicistat, also known as GS9350, is an approved drug for use in the treatment of infection with the human immunodeficiency virus (HIV). Like ritonavir (Norvir), cobicistat is of interest not for its anti-HIV properties, but rather its ability to inhibit liver enzymes that metabolize other medications used to treat HIV, notably elvitegravir, an HIV integrase inhibitor currently under investigation itself. By combining cobicistat with elvitegravir, higher concentrations of elvitgravir are achieved in the body with lower dosing, theoretically enhancing elvitgravir's viral suppression while diminishing its adverse side-effects. In contrast with ritonavir, the only currently approved booster, cobicistat has no anti-HIV activity of its own. Cobicistat is a component of the four-drug, fixed-dose combination HIV treatment elvitegravir/cobicistat/emtricitabine/tenofovir (known as the "Quad Pill"). The Quad Pill was approved by the FDA in August 2012 for use in the United States and is owned by Gilead Sciences.