An Overview of Tybost (Cobicistat)

Brand Name: Tybost
Other Names: COBI
Drug Class: Pharmacokinetic enhancers (CYP3A inhibitors)

Tybost tablet


Some drugs should not be taken with cobicistat. Cobicistat may interact with many drugs, which can cause serious, life-threatening side effects.

When taken with certain other medicines, cobicistat can make existing kidney problems worse. It can also cause new kidney problems, including kidney failure. Your health care provider should check your kidneys before you start and while you are taking cobicistat.

If you are taking cobicistat, tell your health care provider about other prescription and nonprescription medicines, vitamins, nutritional supplements, and herbal products (including St. John's wort) you are taking or plan to take.


While taking cobicistat, it is important to keep all of your appointments with your health care provider.

What Is Cobicistat?

Cobicistat is a prescription medicine approved by the U.S. Food and Drug Administration (FDA) for use in adults one time each day with the HIV medicines atazanavir (brand name: Reyataz) or darunavir (brand name: Prezista) to increase the amount of those medicines in the blood.

Cobicistat is a type of medicine called a pharmacokinetic enhancer. Pharmacokinetic enhancers are used in HIV treatment to increase the amount of other HIV medicines in the blood. When used with atazanavir or darunavir, cobicistat interferes with the breakdown of the drugs in the body. In this way, cobicistat increases the blood levels of atazanavir or darunavir, making them more effective.

Cobicistat is not an HIV medicine and does not treat HIV. Even if you take cobicistat and atazanavir or darunavir, you must also take all the HIV medicines prescribed by your health care provider. Do not cut down on, skip, or stop taking cobicistat or any HIV medicines unless your health care provider tells you to.

What Should I Tell My Health Care Provider Before Taking Cobicistat?

Before taking cobicistat, tell your health care provider:

  • If you are allergic to cobicistat, atazanavir, darunavir, or any other medicines.
  • If you have kidney problems.
  • If you have liver problems.
  • If you have any other medical conditions.
  • If you are pregnant or plan to become pregnant. Whether cobicistat can harm an unborn baby is unknown. Cobicistat should be used during pregnancy only if the potential benefits outweigh the risks. Talk to your health care provider about possible risks with taking cobicistat when pregnant.
  • If you are breastfeeding or plan to breastfeed. Do not breastfeed if you have HIV or are taking cobicistat.
  • If you are using hormone-based birth control (such as pills, implants, or vaginal rings). How hormone-based birth control interacts with cobicistat is unknown. Your health care provider can help you decide how to adjust your birth control while you are taking cobicistat. For more information about using birth control and HIV medicines at the same time, view the AIDSinfo HIV and Birth Control infographic.
  • About other prescription and nonprescription medicines, vitamins, nutritional supplements, and herbal products (particularly St. John's wort) you are taking or plan to take. Cobicistat may affect the way other medicines or products work, and other medicines or products may affect how cobicistat works. Taking cobicistat together with atazanavir or darunavir, along with certain other medicines can lead to severe or life threatening side effects, or death. Keep a list of your medicines and show it to your health care provider and pharmacist when you get a new medicine.

How Should I Take Cobicistat?

Cobicistat (brand name: Tybost) comes in tablet form. Each tablet contains 150 mg of cobicistat.

Take cobicistat according to your health care provider's instructions.

Take cobicistat one time each day at the same time you take atazanavir or darunavir. It is important to take these medicines on a regular dosing schedule.

Do not run out of cobicistat. HIV may become resistant to the HIV medicines atazanavir and darunavir if cobicistat is stopped even for a short time. When your supply starts to run low, get more from your health care provider or pharmacy.

Take cobicistat with food.

If you take too much cobicistat, contact your health care provider or local poison control center (1-800-222-1222) right away, or go to the nearest hospital emergency room.

For more information on how to take cobicistat, see the FDA drug label from DailyMed. (DailyMed is a federal website that includes the most recent drug labels submitted to FDA.)

What Should I Do if I Forget a Dose?

If you miss a dose of cobicistat, take the missed dose as soon as you remember it. But if it is almost time for your next dose, skip the missed dose and just take your next dose at the regular time. Do not take two doses at the same time to make up for the missed dose.

What Side Effects Can Cobicistat Cause?

Cobicistat may cause side effects. Many side effects from HIV medicines, such as nausea or occasional dizziness, are manageable. See the AIDSinfo fact sheet on HIV Medicines and Side Effects for more information that may apply to cobicistat.

Some side effects of cobicistat can be serious. When taken with certain other medicines, cobicistat can make existing kidney problems worse. It can also cause new kidney problems, including kidney failure. (See the WARNING box above.)

The most common side effects of cobicistat with atazanavir include yellowing of the skin or whites of your eyes (jaundice) and rash.

Tell your health care provider if you have any side effect that bothers you or that does not go away.

These are not all the possible side effects of cobicistat. To learn more about possible side effects of cobicistat, read the drug label or package insert or talk to your health care provider or pharmacist.

You can report side effects to FDA at 1-800-FDA-1088 (1-800-332-1088) or online at

How Should Cobicistat Be Stored?

  • Store cobicistat at room temperature, 68°F to 77°F (20°C to 25°C).
  • Keep cobicistat in the container that it came in and keep the container tightly closed. If the container has a small packet of drying agent (called a desiccant), do not remove it. The desiccant protects the medicine from moisture.
  • Do not use cobicistat if the original seal over the container opening is broken or missing.
  • Throw away cobicistat that is no longer needed or expired (out of date). Follow FDA guidelines on how to safely dispose of unused medicine.
  • Keep cobicistat and all medicines out of reach of children.

Where Can I Find More Information About Cobicistat?

More information about cobicistat is available:

  • The cobicistat drug label, from DailyMed. The Patient Counseling Information section of the label includes information for people taking cobicistat.
  • Cobicistat-related research studies, from the AIDSinfo database of study summaries.
  • A list of FDA-approved HIV medicines, from AIDSinfo.

Manufacturer Information

Gilead Sciences, Inc.
Main number: 800-445-3235
Patient assistance: 800-226-2056

The above Patient Version drug summary is based on the following FDA label(s): Tablet (film coated).

[Note from TheBody: This article was originally published by AIDSinfo on May 25, 2018. We have cross-posted it with their permission.]