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Tybost Side Effects

Generic Name: cobicistat

Note: This page contains side effects data for the generic drug cobicistat. It is possible that some of the dosage forms included below may not apply to the brand name Tybost.

For the Consumer

Applies to cobicistat: oral tablet

As well as its needed effects, cobicistat (the active ingredient contained in Tybost) may cause unwanted side effects that require medical attention.

Major Side Effects

If any of the following side effects occur while taking cobicistat, check with your doctor immediately:

Less common:
  • Abdominal or stomach pain
  • bloody urine
  • chills
  • clay-colored stools
  • dark urine
  • decreased frequency or amount of urine
  • dizziness
  • fast heartbeat
  • fever
  • headache
  • hives or welts, itching, or rash
  • hoarseness
  • increased thirst
  • irritation
  • joint pain, stiffness, or swelling
  • loss of appetite
  • lower back or side pain
  • nausea and vomiting
  • pain in the groin or genitals
  • redness of the skin
  • sharp back pain just below the ribs
  • swelling of the eyelids, face, lips, hands, lower legs, or feet
  • tightness in the chest
  • troubled breathing or swallowing
  • unpleasant breath odor
  • unusual tiredness or weakness
  • vomiting of blood
  • weight gain
  • yellow eyes or skin
Less common or rare:
  • Dark-colored urine
  • muscle cramps or spasms
  • muscle pain or stiffness

Minor Side Effects

Some cobicistat side effects may not need any medical attention. As your body gets used to the medicine these side effects may disappear. Your health care professional may be able to help you prevent or reduce these side effects, but do check with them if any of the following side effects continue, or if you are concerned about them:

Less common or rare:
  • Diarrhea
  • discouragement
  • feeling sad or empty
  • irritability
  • loss of interest or pleasure
  • trouble concentrating
  • trouble sleeping
  • upper abdominal or stomach pain

For Healthcare Professionals

Applies to cobicistat: oral tablet


In a clinical trial, safety of this drug was evaluated in therapy-naive patients using cobicistat-boosted atazanavir with emtricitabine-tenofovir. The most commonly reported side effects were associated with elevated bilirubin levels including jaundice, ocular icterus, and nausea. Study drug was discontinued due to side effects in 7% of patients in the cobicistat-boosted group; 4.9% discontinued due to bilirubin-related side effects.[Ref]


In 1 clinical trial, hyperbilirubinemia (greater than 1 times the upper limit of normal [1 x ULN]) was reported in 97.7% of patients in the cobicistat-boosted atazanavir group and 97.4% in the ritonavir-boosted atazanavir group. Increases in total bilirubin greater than 2 x ULN was reported in 85.7% of patients in the cobicistat-boosted group and 77.7% in the ritonavir-boosted group. Increases in total bilirubin greater than 2.5 x ULN was reported in 65% of patients in the cobicistat-boosted group and 56% in the ritonavir-boosted group. Increased ALT or AST (greater than 3 x ULN) was reported in 12% of patients in the cobicistat-boosted group and 8.7% in the ritonavir-boosted group. Increased ALT (greater than 5 x ULN), AST (greater than 5 x ULN), and GGT (greater than 5 x ULN) were reported in 3%, 3%, and 2% of patients in the cobicistat-boosted group, respectively.[Ref]

Very common (10% or more): Hyperbilirubinemia, increased total bilirubin, jaundice (up to 13%), increased ALT or AST
Common (1% to 10%): Increased ALT, increased AST, increased GGT[Ref]


Very common (10% or more): Ocular icterus (up to 15%)[Ref]


Increased serum amylase (greater than 2 x ULN) was reported in up to 4% of patients in the cobicistat-boosted group.

If serum amylase was greater than 1.5 x ULN, lipase was also measured. Increased lipase (grades 3 to 4) was reported in up to 9% of patients in the cobicistat-boosted group.[Ref]

Very common (10% or more): Nausea (up to 12%)
Common (1% to 10%): Vomiting, diarrhea, dyspepsia, abdominal pain, abdominal distension, flatulence, dry mouth, increased lipase, increased serum amylase
Frequency not reported: Upper abdominal pain[Ref]


Common (1% to 10%): Increased creatine kinase
Uncommon (0.1% to 1%): Myalgia
Frequency not reported: Rhabdomyolysis[Ref]

Increased creatine kinase (at least 10 x ULN) was reported in up to 6% of patients in the cobicistat-boosted group.[Ref]


Increased urine RBC (greater than 75 RBC/high power field) and urine glucose (at least 1000 mg/dL) have been reported in up to 4% and 3% of patients in the cobicistat-boosted group, respectively.[Ref]

Common (1% to 10%): Hematuria (increased urine RBC), glycosuria (increased urine glucose)
Uncommon (0.1% to 1%): Proteinuria[Ref]


Nephrolithiasis has been reported with atazanavir. In clinical trials, nephrolithiasis was reported in 2% of patients in the cobicistat-boosted group and no patients in the ritonavir-boosted group. Onset of nephrolithiasis was about 24 weeks.

Renal impairment (including acute renal failure and Fanconi syndrome) has been reported when this drug was used in regimen containing tenofovir.[Ref]

Common (1% to 10%): Nephrolithiasis
Frequency not reported: Decreased estimated CrCl, increased serum creatinine, tubular secretion of creatinine inhibited (actual renal glomerular function not affected), renal impairment (including acute renal failure, Fanconi syndrome), nephropathy, Fanconi syndrome acquired[Ref]

Nervous system

Common (1% to 10%): Headache, dizziness, somnolence, dysgeusia[Ref]


Common (1% to 10%): Hyperglycemia, increased appetite
Frequency not reported: Increased fasted total cholesterol, increased fasted high-density lipoprotein cholesterol, increased fasted low-density lipoprotein cholesterol, increased fasted triglycerides[Ref]


Common (1% to 10%): Fatigue
Uncommon (0.1% to 1%): Pyrexia, asthenia[Ref]


Common (1% to 10%): Insomnia, abnormal dreams
Uncommon (0.1% to 1%): Depression, sleep disorder[Ref]


Common (1% to 10%): Rash (rash events included allergic dermatitis, drug hypersensitivity, generalized pruritus, eosinophilic pustular folliculitis, rash, generalized rash, macular rash, maculopapular rash, morbilliform rash, papular rash, urticaria)
Uncommon (0.1% to 1%): Pruritus[Ref]


1. Cerner Multum, Inc. "UK Summary of Product Characteristics." O 0

2. EMEA. European Medicines Agency "EPARs. European Union Public Assessment Reports. Available from: URL:"

3. Cerner Multum, Inc. "Australian Product Information." O 0

4. "Product Information. Tybost (cobicistat)." Gilead Sciences, Foster City, CA.

It is possible that some side effects of Tybost may not have been reported. These can be reported to the FDA here. Always consult a healthcare professional for medical advice.

Disclaimer: Every effort has been made to ensure that the information provided is accurate, up-to-date and complete, but no guarantee is made to that effect. In addition, the drug information contained herein may be time sensitive and should not be utilized as a reference resource beyond the date hereof. This material does not endorse drugs, diagnose patients, or recommend therapy. This information is a reference resource designed as supplement to, and not a substitute for, the expertise, skill , knowledge, and judgement of healthcare practitioners in patient care. The absence of a warning for a given drug or combination thereof in no way should be construed to indicate safety, effectiveness, or appropriateness for any given patient. does not assume any responsibility for any aspect of healthcare administered with the aid of materials provided. The information contained herein is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. If you have questions about the substances you are taking, check with your doctor, nurse, or pharmacist.