What the label lists and what reports show
Famciclovir side effects
Famciclovir's FDA label: “The most common adverse events reported in at least 1 indication by greater than 10% of adult patients treated with famciclovir are headache and nausea.” FAERS holds 2,753 reports naming it through July 30, 2026; the reaction reported most often, leaving out the conditions it is used for, product-use terms and outcomes, is fatigue (191 reports).
- Generic listed
Check it at the source: the famciclovir FDA label on DailyMed (effective September 17, 2025, Macleods Pharmaceuticals Limited); the FDA FAERS public dashboard.
What does the patient leaflet say about side effects?
From the patient leaflet: What are the possible side effects of famciclovir tablets?The most common side effects of famciclovir tablets are headache and nausea. These are not all the possible side effects of famciclovir tablets. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.
Source: FDA drug label (Famciclovir), Aurobindo Pharma Limited, effective June 15, 2024 (SPL set fcf0b0fa-bb2c-4f2c-aa9f-1f2da65d8343), via openFDA; the full label on DailyMed
What does the label list?
From the label: adverse reactionsThe most common adverse events reported in at least 1 indication by greater than 10% of adult patients treated with famciclovir are headache and nausea.
Table 2: Selected Adverse Events (all grades and without regard to causality) Reported by…
| Reaction | Famciclovir (n=273) % | Placebo (n=146) % | Famciclovir (n=163) % | Placebo (n=166) % | Famciclovir (n=458) % | Placebo (n=63) % | Famciclovir (n=447) % | Placebo (n=254) % |
|---|---|---|---|---|---|---|---|---|
| Headache | 22.7 | 17.8 | 13.5 | 5.4 | 39.3 | 42.9 | 8.5 | 6.7 |
| Paresthesia | 2.6 | 0.0 | 0.0 | 0.0 | 0.9 | 0.0 | 0.0 | 0.0 |
| Migraine | 0.7 | 0.7 | 0.6 | 0.6 | 3.1 | 0.0 | 0.2 | 0.0 |
| Nausea | 12.5 | 11.6 | 2.5 | 3.6 | 7.2 | 9.5 | 2.2 | 3.9 |
| Diarrhea | 7.7 | 4.8 | 4.9 | 1.2 | 9.0 | 9.5 | 1.6 | 0.8 |
| Vomiting | 4.8 | 3.4 | 1.2 | 0.6 | 3.1 | 1.6 | 0.7 | 0.0 |
| Flatulence | 1.5 | 0.7 | 0.6 | 0.0 | 4.8 | 1.6 | 0.2 | 0.0 |
| Abdominal Pain | 1.1 | 3.4 | 0.0 | 1.2 | 7.9 | 7.9 | 0.2 | 0.4 |
| Fatigue | 4.4 | 3.4 | 0.6 | 0.0 | 4.8 | 3.2 | 1.6 | 0.4 |
| Pruritus | 3.7 | 2.7 | 0.0 | 0.6 | 2.2 | 0.0 | 0.0 | 0.0 |
| Rash | 0.4 | 0.7 | 0.0 | 0.0 | 3.3 | 1.6 | 0.0 | 0.0 |
| Dysmenorrhea | 0.0 | 0.7 | 1.8 | 0.6 | 7.6 | 6.3 | 0.4 | 0.0 |
Rows and numbers as the label prints them, under its own column headings (the first rows of a longer table where it runs on). A reaction in a trial table is not necessarily caused by the medicine, and trials differ from everyday use.
From the label: adverse reactions, continuedAcute renal failure is discussed in greater detail in other sections of the label [see Warnings and Precautions ( 5 )]. The most common adverse events reported in at least 1 indication by greater than 10% of adult patients treated with famciclovir are headache and nausea. The most common adverse events reported in at least 1 indication by greater than 10% of adult patients are headache and nausea. ( 6.1 ) To report SUSPECTED ADVERSE REACTIONS, contact Macleods Pharma USA, Inc. at 1-888-943-3210 or 1-855-926-3384 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch 6.1 Clinical Trials Experience in Adult Patients Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared with rates in the clinical trials of another drug and may not reflect the rates observed in practice. Immunocompetent patients: The safety of famciclovir has been evaluated in active- and placebo-controlled clinical studies involving 816 famciclovir treated patients with herpes zoster (famciclovir, 250 mg three times daily to 750 mg three times daily); 163 famciclovir treated patients with recurrent genital herpes ( famciclovir, 1000 mg twice daily); …
Source: FDA drug label, Macleods Pharmaceuticals Limited, effective September 17, 2025 (SPL set eeeee9c4-8566-4100-8ca4-3df936a3365d), via openFDA; the full label on DailyMed
What do FAERS reports show?
2,753 reports list famciclovir among the medicines taken, each a report of something that happened, not proof the medicine caused it; 274 are coded as a death and 859 as a hospital stay. Counts follow how widely a medicine is used and watched, and they are not a measure of how risky it is. Of the 21 reactions below, 8 are named by the same term (in US spelling) in the label's adverse reactions, warnings or patient leaflet; a reaction the label does not name may still be there under another word, and a report does not show that the medicine caused it.
Reports received each year
The 25 most reported reactions
Source: FDA Adverse Event Reporting System (FAERS) via openFDA, reports through July 30, 2026; reactions as MedDRA preferred terms
What next?
- Famciclovir: the full record
- label, generics, price, shortages, recalls
- Report a side effect to the FDA
- MedWatch
- Side effects hub
- the most reported medicines and reactions