Cobicistat is a drug used to boost other medications in the blood to make them more effective. Currently, a small dose of ritonavir is often prescribed to perform this function.  

Cobicistat is not active against HIV.  It works by inhibiting an enzyme called CYP3A4 that is responsible for breaking down (or metabolism) of certain medications, including several HIV drugs. This helps boost the effectiveness of these drugs, while allowing fewer pills or doses on a daily basis.

Cobicistat is contained in the coformulation Stribild.  Cobicistat does not have any anti-HIV treatment properties.

Basic info

Generic name Cobicistat
Brand name Tybost (UK & US)
Also known as GS-9350
Drug class Pharmacokinetic Enhancers
Pediatric dosing? Available in doses suitable for children and/or young people.
Availability in Australia Not available on the Pharmaceutical Benefits Scheme (PBS)
This drug may be available through clinical trials in Australia.

Taking it


The cobicist dose is 150 mg, once a day, in combination with HIV medications that require boosting. Stribid contains 150 mg cobicistat.  Cobicistat was developed to be used in combination with other drugs.

Regardless of what you read on this website or elsewhere, you should always take your medications according to your doctor's instructions. If you're unsure, speak to your doctor or pharmacist.

Side effect

All drugs can produce side effects in some people. These may be mild, moderate or severe, so you should be aware of potential side effects before starting any drug, and speak to your doctor if you experience side effects that concern you.

  • Common side effects may include nausea (upset stomach, feeling sick to the stomach), vomiting, diarrhea.
  • Less common side effects may include kidney impairment.
  • It's unlikely you will experience all of these side effects, and you may not experience any side effects at all. Before starting any new drug, ask your doctor about side effects you might experience and discuss strategies for dealing with side effects if they do occur. If you experience any significant side effect you should continue taking your medicine and see your doctor as soon as possible.

Interactions with other drugs

Studies on potential interactions between cobicistat and other drugs have not yet been reported, but are planned and ongoing.