valacyclovir Side Effects
Also known as: Valtrex
Analysis of 39,048 adverse event reports submitted to the FDA from 2004 to 2025.
Total Reports
39,048
Death-Related
3,520
9.0% of reports
Hospitalizations
15,607
40.0% of reports
Top Indication
Product Used For Unknown Indication
Most Reported Adverse Reactions
Who Reports Side Effects
Gender Distribution
Age Distribution
Reporting Trend by Year
Reactions in Death Reports
Top reactions reported in 3,520 reports where death was an outcome. These are voluntarily reported and do not establish causation.
| Reaction | Reports |
|---|---|
| DEATH | 1,041 |
| OFF LABEL USE | 318 |
| PNEUMONIA | 217 |
| THROMBOCYTOPENIA | 214 |
| NEUTROPENIA | 205 |
| PYREXIA | 199 |
| SEPTIC SHOCK | 195 |
| DISEASE PROGRESSION | 187 |
| SEPSIS | 183 |
| DIARRHOEA | 155 |
| FEBRILE NEUTROPENIA | 147 |
| ANAEMIA | 143 |
| PLASMA CELL MYELOMA | 131 |
| RESPIRATORY FAILURE | 124 |
| ACUTE KIDNEY INJURY | 121 |
| INFECTION | 115 |
| NAUSEA | 115 |
| MULTIPLE ORGAN DYSFUNCTION SYNDROME | 114 |
| HYPOTENSION | 107 |
| CYTOKINE RELEASE SYNDROME | 105 |
Reactions in Hospitalization Reports
Top reactions in 15,607 reports where hospitalization was an outcome.
| Reaction | Reports |
|---|---|
| FEBRILE NEUTROPENIA | 1,189 |
| PNEUMONIA | 1,115 |
| PYREXIA | 1,012 |
| OFF LABEL USE | 912 |
| ACUTE KIDNEY INJURY | 843 |
| DIARRHOEA | 799 |
| FATIGUE | 630 |
| CYTOKINE RELEASE SYNDROME | 627 |
| NAUSEA | 607 |
| NEUTROPENIA | 507 |
| THROMBOCYTOPENIA | 498 |
| DYSPNOEA | 493 |
| COVID-19 | 492 |
| ASTHENIA | 473 |
| VOMITING | 445 |
| ANAEMIA | 435 |
| FALL | 431 |
| SEPSIS | 400 |
| HEADACHE | 383 |
| PAIN | 371 |
Nearby — Related Medications
What the FAERS Data Reveals About valacyclovir Side Effects
The FDA Adverse Event Reporting System (FAERS) contains 39,048 voluntary reports linked to valacyclovir and its brand equivalents (Valtrex), spanning 2004 through 2025. Of those, 3,520 (9.0%) listed death as an outcome and 15,607 (40.0%) 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, 56% were female and 44% male; age distribution skews toward 45-64, with 9,470 reports in that bracket. The single most reported reaction is off label use with 2,544 submissions, followed by fatigue and diarrhoea.
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.
Read our methodology — how this data is sourced, computed, and verified.