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Famciclovir Side Effects

Medically reviewed by Last updated on Aug 22, 2023.


Commonly reported side effects of famciclovir include: headache. Continue reading for a comprehensive list of adverse effects.

Applies to famciclovir: oral tablets.

Side effects include:

Headache, nausea, diarrhea, vomiting.

For Healthcare Professionals

Applies to famciclovir: oral tablet.


Famciclovir is generally well tolerated. The most common side effects reported in at least 1 indication by greater than 10% of patients are headache and nausea.[Ref]

Nervous system

Confusion and bradykinesia developed in an 80-year-old woman who received famciclovir for acute herpes zoster. The dosage administered was clinically appropriate and adjusted to her estimated creatinine clearance. Although herpes zoster may sometimes elicit neurological complications and cannot be ruled out as a contributing factor, the patient's mobility problems and mental deterioration corresponded temporally with drug administration (onset within 48 and 72 hours, respectively, of initiation and reinstitution of therapy).[Ref]

Very common (10% or more): Headache (up to 39.3%)

Common (1% to 10%): Migraine (up to 3.1%), paresthesia (up to 2.6%)

Frequency not reported: Insomnia

Postmarketing reports: Dizziness, somnolence[Ref]


An isolated case of acute necrotic-hemorrhagic pancreatitis occurred in a kidney graft recipient who was treated with famciclovir for severe hepatitis B infection. The author could not identify any other etiologic factor for the pancreatitis, although some possible predisposing factors were noted, including the patient's liver insufficiency and renal dysfunction.[Ref]

Very common (10% or more): Nausea (up to 13%)

Common (1% to 10%): Diarrhea (up to 9%), abdominal pain (up to 7.9%), vomiting (up to 5%), elevated lipase (greater than 1.5 times normal range high [NRH]; 4.9%), flatulence (up to 4.8%), elevated amylase (greater than 1.5 times NRH; 1.5%)

Rare (less than 0.1%): Pancreatitis

Frequency not reported: Dyspepsia, anorexia[Ref]


Common (1% to 10%): Dysmenorrhea (up to 7.6%)[Ref]


Common (1% to 10%): Fatigue (up to 4.8%)

Frequency not reported: Injury, back pain, viral infection (including influenza, influenza-like symptoms, and symptoms of a cold), asthenia, fever[Ref]


Common (1% to 10%): Pruritus (up to 3.7%), rash (up to 3.3%)

Postmarketing reports: Urticaria, erythema multiforme, Stevens-Johnson syndrome, toxic epidermal necrolysis, angioedema (e.g., face, eyelid, periorbital, and pharyngeal edema), leukocytoclastic vasculitis[Ref]


Common (1% to 10%): Neutropenia (less than 0.8 times normal range low [NRL]; 3.2%), leukopenia (less than 0.75 times NRL; 1.3%)

Uncommon (0.1% to 1%): Anemia (less than 0.8 times NRL; 0.1%)

Postmarketing reports: Thrombocytopenia[Ref]


Common (1% to 10%): Elevated ALT (greater than 2 times NRH; 3.2%), elevated AST (greater than 2 times NRH; 2.3%), elevated total bilirubin (greater than 1.5 times NRH; 1.9%)

Postmarketing reports: Cholestatic jaundice, abnormal liver function tests[Ref]


Uncommon (0.1% to 1%): Elevated serum creatinine (greater than 1.5 times NRH; 0.2%)

Frequency not reported: Acute renal failure[Ref]


Postmarketing reports: Palpitations


Postmarketing reports: Confusion (including delirium, disorientation, and confusional state occurring predominantly in the elderly), hallucinations


Frequency not reported: Upper respiratory tract infection, pharyngitis[Ref]


1. Product Information. Famvir (famciclovir). SmithKline Beecham. 2001.

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3. DiazMitoma F, Sibbald RG, Shafran SD, Boon R, Saltzman RL. Oral famciclovir for the suppression of recurrent genital herpes: A randomized controlled trial. JAMA. 1998;280:887-92.

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9. Gales BJ, Gales MA. Confusion and bradykinesia associated with famciclovir therapy for herpes zoster. Am J Health Syst Pharm. 1996;53:1454,1456.

10. Tyring S, Belanger R, Bezwoda W, Ljungman P, Boon R, Saltzman RL. A randomized, double-blind trial of famciclovir versus acyclovir for the treatment of localized dermatomal herpes zoster in immunocompromised patients. Cancer Invest. 2001;19:13-22.

11. Spruance SL, Bodsworth N, Resnick H, et al. Single-dose, patient-initiated famciclovir: A randomized, double-blind, placebo-controlled trial for episodic treatment of herpes labialis. J Am Acad Dermatol. 2006;55:47-53.

12. Dworkin RH, Johnson RW, Breuer J, et al. Recommendations for the management of herpes zoster. Clin Infect Dis. 2007;44 Suppl 1:S1-S26.

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14. Abudalu M, Tyring S, Koltun W, Bodsworth N, Hamed K. Single-day, patient-initiated famciclovir therapy versus three-day valacyclovir regimen for recurrent genital herpes: a randomized, double-blind, comparative trial. Clin Infect Dis. 2008;47:651-8.

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Some side effects may not be reported. You may report them to the FDA.