Many medications can cause side effects. A side effect is an unwanted response to a medication when it is taken in normal doses. Side effects can be mild or severe, temporary or permanent.

The side effects listed below are not experienced by everyone who takes Tybost (Cobicistat). If you are concerned about side effects, discuss the risks and benefits of Tybost (Cobicistat) with your doctor.

The following side effects have been reported by at least 1% of people taking Tybost (Cobicistat). Many of these side effects can be managed, and some may go away on their own over time.

Contact your doctor if you experience these side effects and they are severe or bothersome. Your pharmacist may be able to advise you on managing side effects.

• nausea
• rash

Although most of the side effects listed below don't happen very often, they could lead to serious problems if you do not seek medical attention.

Check with your doctor as soon as possible if any of the following side effects occur:

• unexpected muscle pain
• yellowing of the skin or eyes

Stop taking the medication and seek immediate medical attention if any of the following occur:

• symptoms of a serious allergic reaction such as swelling of the face or throat, Hives, or difficulty breathing

Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking Tybost (Cobicistat).

Each orange, round, biconvex, film-coated tablet, debossed with "GSI" on one side and plain-faced on the other side contains 150 mg of Tybost (Cobicistat). Nonmedicinal ingredients: silicon dioxide, microcrystalline cellulose, croscarmellose sodium, and magnesium stearate; coating: polyethylene glycol, polyvinyl alcohol, talc, titanium dioxide, sunset yellow FCF (FD&C Yellow No. 6) aluminum lake, and iron oxide yellow.

Do not take Tybost (Cobicistat) if you:

• are allergic to Tybost (Cobicistat) or any ingredients of the medication
• are taking any other medications that contain Tybost (Cobicistat) (combination products to treat HIV)
• are taking any of the following medications:
• Alfuzosin
• astemizole
• cisapride
• ergot-containing medications (e.g., diydroergotamine, ergonovine, ergotamine, methylergonovine)
• Lovastatin
• midazolam
• Pimozide
• rifampin
• St. John's wort
• Salmeterol
• seizure medications: Carbamazepine, Phenobarbital, Phenytoin
• Sildenafil (when used to treat lung problems)
• Simvastatin
• Triazolam

There may be an interaction between Tybost (Cobicistat) and any of the following:

• alpha blockers (e.g., alfuzosin, Doxazosin, Silodosin, Tamsulosin)
• antiarrhythmics (e.g., Amiodarone, dofetilide, Mexiletine, procainamide, quinidine)
• anti-cancer medications (e.g., Cabazitaxel, Docetaxel, Doxorubicin, Etoposide, Ifosfamide, Irinotecan, Vincristine)
• certain antihistamines (e.g., Chlorpheniramine, Hydroxyzine)
• anti-psychotic medications (e.g., Chlorpromazine, Clozapine, Haloperidol, Olanzapine, Quetiapine, Risperidone)
• Aprepitant
• Apixaban
• Atomoxetine
• "azole" antifungals (e.g., itraconazole, ketoconazole, Voriconazole)
• benzodiazepines (e.g., Chlordiazepoxide, Clonazepam, Diazepam, Lorazepam, triazolam)
• beta-blockers (e.g., Carvedilol, Metoprolol, Propranolol)
• birth control pills
• Bosentan
• Bromocriptine
• Buspirone
• Calcitriol
• calcium channel blockers (e.g., Amlodipine, Diltiazem, Nifedipine, Verapamil)
• cannabis
• carbamazepine
• chloroquine
• Colchicine
• conivaptan
• inhaled corticosteroids (e.g., budesonide, ciclesonide, fluticasone)
• oral corticosteroids (e.g., Dexamethasone, Hydrocortisone, Prednisone)
• Cyclosporine
• dabigatran
• Darifenacin
• Deferasirox
• Dextromethorphan
• Domperidone
• Dutasteride
• Enzalutamide
• ergot alkaloids (e.g., Dihydroergotamine, ergonovine,  ergotamine, methylergonovine)
• estrogens (e.g., conjugated estrogen, Estradiol, ethinyl estradiol)
• Everolimus
• Guanfacine
• hepatitis C protease inhibitors (e.g., asunaprevir,,grazoprevir,  simeprevir,)
• HIV non-nucleoside reverse transcriptase inhibitors (NNRTIs; e.g., delavirdine, efavirenz, etravirine, nevirapine)
• HIV protease inhibitors (e.g., atazanavir, indinavir, ritonavir, saquinavir)
• Lomitapide
• Losartan
• macrolide antibiotics (e.g., clarithromycin, erythromycin)
• Maprotiline
• maraviroc
• Mefloquine
• Methadone
• methamphetamine
• mifepristone
• Mirtazapine
• Modafinil
• narcotic pain relievers (e.g., Fentanyl, Hydrocodone, Oxycodone)
• Naloxegol
• nefazodone
• nitrates (e.g., isosorbide dinitrate,  isosorbide mononitrate)
• Orlistat
• Oxcarbazepine
• oxybutinyn
• phenobarbital
• phenytoin
• phosphodiesterase-5 inhibitors (e.g., sildenafil, Tadalafil, Vardenafil)
• Prasugrel
• praziquantel
• Primaquine
• primidone
• progestins (e.g., Dienogest, Levonorgestrel, medroxyprogesterone, Norethindrone)
• proton pump inhibitors (e.g., Lansoprazole, Omeprazole)
• quinine
• Repaglinide
• rifabutin
• rifampin
• rilpivirine
• Riociguat
• Romidepsin
• salmeterol
• selective serotonin reuptake inhibitors (SSRIs; e.g., Citalopram, Fluoxetine, Paroxetine, Sertraline)
• serotonin-norepinephrine reuptake inhibitors (e.g., Duloxetine, Venlafaxine)
• Sirolimus
• Solifenacin
• "statin" anti-cholesterol medications (e.g., Atorvastatin, lovastatin, simvastatin)
• Tacrolimus
• Tamoxifen
• Tetrabenazine
• Ticagrelor
• Tocilizumab
• Tolterodine
• Tolvaptan
• Trazodone
• tricyclic antidepressants (e.g., Amitriptyline, Clomipramine, Desipramine, Trimipramine)
• tyrosine kinase inhibitors (e.g., Bosutinib, Dasatinib, imatinib, Nilotinib)
• Ulipristal
• Warfarin
• Zolpidem
• Zopiclone

If you are taking any of these medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:

• stop taking one of the medications,
• change one of the medications to another,
• change how you are taking one or both of the medications, or
• leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. Speak to your doctor about how any drug interactions are being managed or should be managed.

Medications other than those listed above may interact with Tybost (Cobicistat). Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the Nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.

Before you begin using a medication, be sure to inform your doctor of any medical conditions or Allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should use Tybost (Cobicistat).

Fat redistribution: Over time, Tybost (Cobicistat) may change how fat is distributed in your body and may change your body shape. You may notice increased fat in the upper back and neck, breast, around the back, chest, and stomach area; or loss of fat from the legs, arms, and face. The long-term effects of this are not known.

Hepatitis B and Hepatitis C Infection: The safety and effectiveness of using Tybost (Cobicistat) with co-existing liver disorders have not well been studied. People with chronic hepatitis B or C who are also using antiretroviral medications are at an increased risk of developing severe and possibly fatal liver problems. Your doctor may test for hepatitis B and hepatitis C before prescribing Tybost (Cobicistat). If you have a history of other liver disease, discuss with your doctor how Tybost (Cobicistat) may affect your medical condition, how your medical condition may affect the dosing and effectiveness of Tybost (Cobicistat), and whether any special monitoring is needed.

Immune reconstitution syndrome: Tybost (Cobicistat) may cause immune reconstitution syndrome, where signs and symptoms of inflammation from previous infections appear. These symptoms occur soon after starting anti-HIV medication and can vary. They are thought to occur as a result of the immune system improving and being able to fight infections that have been present without symptoms (such as pneumonia, herpes, hepatitis, or Tuberculosis). Report any new symptoms to your doctor immediately.

Kidney function: Tybost (Cobicistat) may cause a slight decrease in kidney function. While this is not normally a problem, if it is combined with another anti-HIV medication, tenofovir, it may cause kidney failure. If you have decreased kidney function or Kidney Disease, discuss with your doctor how Tybost (Cobicistat) may affect your medical condition, how your medical condition may affect the dosing and effectiveness of Tybost (Cobicistat), and whether any special monitoring is needed. Tybost (Cobicistat) is not recommended for people with severely reduced kidney function.

Liver function: The safety and effectiveness of using Tybost (Cobicistat) with liver disorders have not well been studied. People with chronic hepatitis B or C who are also using antiretroviral medications are at an increased risk of developing severe and possibly fatal liver problems. If you have decreased liver function or liver disease, discuss with your doctor how Tybost (Cobicistat) may affect your medical condition, how your medical condition may affect the dosing and effectiveness of Tybost (Cobicistat), and whether any special monitoring is needed. Tybost (Cobicistat) is not recommended for people with severely reduced liver function.

Pregnancy: Tybost (Cobicistat) should not be used during pregnancy unless the benefits outweigh the risks. If you become pregnant while taking Tybost (Cobicistat), contact your doctor immediately.

Breast-feeding: It is not known if Tybost (Cobicistat) passes into breast milk. Women who have HIV infection are cautioned against breast-feeding because of the risk of passing HIV to a baby who does not have the infection.

Children: The safety and effectiveness of using Tybost (Cobicistat) have not been established for children.