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Famvir Side Effects

Generic name: famciclovir

Medically reviewed by Last updated on Aug 22, 2022.

Note: This document contains side effect information about famciclovir. Some of the dosage forms listed on this page may not apply to the brand name Famvir.


Common side effects of Famvir include: headache. See below for a comprehensive list of adverse effects.

For the Consumer

Applies to famciclovir: oral tablets

Side effects include:

Headache, nausea, diarrhea, vomiting.

For Healthcare Professionals

Applies to famciclovir: oral tablet


Famciclovir (the active ingredient contained in Famvir) 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 (the active ingredient contained in Famvir) 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 (the active ingredient contained in Famvir) 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):

2. Luber AD, Flaherty JF "Famciclovir for treatment of herpesvirus infections." Ann Pharmacother 30 (1996): 978-85

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 280 (1998): 887-92

4. Wald A "New therapies and prevention strategies for genital herpes." Clin Infect Dis 28 (1999): s4-13

5. Romanowski B, Aoki FY, Martel AY, Lavender EA, Parsons JE, Saltzman RL "Efficacy and safety of famciclovir for treating mucocutaneous herpes simplex infection in HIV-infected individuals." Aids 14 (2000): 1211-7

6. Sacks SL, Aoki FY, Martel AY, Shafran SD, Lassonde M "Clinic-initiated, twice-daily oral famciclovir for treatment of recurrent genital herpes: a randomized, double-blind, controlled trial." Clin Infect Dis 41 (2005): 1097-104

7. Aoki FY, Tyring S, Diaz-Mitoma F, Gross G, Gao J, Hamed K "Single-day, patient-initiated famciclovir therapy for recurrent genital herpes: a randomized, double-blind, placebo-controlled trial." Clin Infect Dis 42 (2006): 8-13

8. Saltzman R, Jurewicz R, Boon R "Safety of famciclovir in patients with herpes zoster and genital herpes." Antimicrob Agents Chemother 38 (1994): 2454-7

9. Gales BJ, Gales MA "Confusion and bradykinesia associated with famciclovir therapy for herpes zoster." Am J Health Syst Pharm 53 (1996): 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 19 (2001): 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 55 (2006): 47-53

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

13. Simpson D, Lyseng-Williamson KA "Famciclovir: a review of its use in herpes zoster and genital and orolabial herpes." Drugs 66 (2006): 2397-416

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 47 (2008): 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.