acyclovir Side Effects

What the FAERS Data Reveals About acyclovir Side Effects

The FDA Adverse Event Reporting System (FAERS) contains 109,698 voluntary reports linked to acyclovir and its brand equivalents (Zovirax), spanning 2003 through 2025. Of those, 13,944 (12.7%) listed death as an outcome and 40,651 (37.1%) involved hospitalization. The most common indication reported alongside adverse events was Product Used For Unknown Indication.

Demographic breakdowns help contextualize who is being exposed to the drug. Of reports with known sex, 50% were female and 50% male; age distribution skews toward 45-64, with 23,378 reports in that bracket. The single most reported reaction is fatigue with 7,612 submissions, followed by diarrhoea and off label use.

FAERS is a signal-detection tool, not a scorecard. Reports are voluntary, and a single case may list multiple suspect drugs, so numbers above should not be read as incidence rates or per-patient risk. Widely prescribed drugs naturally accumulate more reports than niche therapies even when individual risk is low. These aggregates are useful for spotting patterns that merit further pharmacovigilance, not for choosing between medications. This page is for educational reference only and is not medical advice — speak with a licensed clinician about any side-effect concerns.