Cobicistat, sold under the brand name Tybost, is a medication for use in the treatment of human immunodeficiency virus infection (HIV/AIDS).

In contrast with ritonavir, the only other booster approved for use as a part of HAART, cobicistat has no anti-HIV activity of its own.

It also inhibits intestinal transport proteins, increasing the overall absorption of several HIV medications, including atazanavir, darunavir, and tenofovir alafenamide.

[6] Cobicistat is therefore able to increase plasma concentration of other coadministered anti-HIV drugs without the risk of causing cobicistat-resistant mutations in the HIV virus.

These studies were conducted by scientists at Gilead Sciences, and successfully optimized ritonavir into a potent CYP3A inhibitor lacking anti-HIV activity.