Prescription medication · Antiviral
valacyclovir
Also sold as Valtrex. Valacyclovir treats cold sores, genital herpes, and shingles.
Data updated 2026-05-15
- 39,048
- FDA reportsModerately reported
- 3
- InteractionsFew interactions
- 98% less
- Generic vs brandHuge savings
- $20.32
- Brand price (NADAC)
What the data shows
valacyclovir (Valtrex) is a prescription Antiviral, reported at a middle-of-the-pack volume (39,048 FDA reports), whose generic costs a fraction of the brand (about 98% less).
Reporting volume reflects how widely a drug is used and studied, not how dangerous it is, a FAERS report documents a temporal association, never proof of cause.
valacyclovir (Valtrex) is a prescription Antiviral. Valacyclovir treats cold sores, genital herpes, and shingles.
Valacyclovir is an antiviral medicine. It is used to treat infections caused by certain viruses.
Verify with FDA → · CMS NADAC pricing →
Drug Pricing (NADAC)
Brand Price
$20.32/unit
Generic Price
$0.43/unit
Generic Savings
98%
Generic Available
Yes (7 manufacturers)
Pricing data from NADAC (CMS), effective December 18, 2024. Compare all drug costs →
What it does
Valacyclovir treats cold sores, genital herpes, and shingles.
Common side effects
Headache, Nausea, Abdominal pain
Key warnings
Valacyclovir can cause serious problems like TTP/HUS, which is a blood disorder.
The sections below are summarized in plain English from valacyclovir's FDA-approved prescribing information. They describe what the official label says, and are not personal medical advice.
How It Works
Valacyclovir stops the virus from growing and spreading. It does this by blocking a key enzyme the virus needs to reproduce. This helps your body fight off the infection.
How to Take It
You can take valacyclovir with or without food. For cold sores, the usual dose is 2 grams every 12 hours for 1 day. For genital herpes, the dose and how long you take it depends on whether it's your first outbreak or a repeat outbreak. Follow your doctor's instructions carefully.
This is a plain-language summary of valacyclovir's FDA labeling, not individualized dosing advice. Ask a pharmacist or prescriber before changing how you take this medication.
Pregnancy & Breastfeeding
Tell your doctor if you are pregnant or plan to become pregnant. Studies haven't shown a risk of major birth defects, but there isn't enough data to be sure about miscarriage or other problems. Talk to your doctor about the risks and benefits.
This is a plain-language summary of valacyclovir's FDA labeling, not individualized advice. Ask a pharmacist or prescriber about pregnancy or breastfeeding on this medication.
Missed Dose
If you miss a dose, take it as soon as you remember. If it is close to your next dose, skip the missed dose and continue with your regular schedule.
This is a plain-language summary of valacyclovir's FDA labeling, not individualized advice. Ask a pharmacist or prescriber what to do about your specific missed dose.
Storage
Store valacyclovir tablets at room temperature, away from heat and moisture.
Side Effects (from patient reports)
Based on 39,048 FDA adverse event reports.
Most-reported reactions
Adverse reactions in FAERS for valacyclovir, by number of reports
- Feeling very tired
Feeling very tired
2,294 reports
- Loose, watery stools
Loose, watery stools
2,120 reports
- Feeling sick to your stomach
Feeling sick to your stomach
1,838 reports
- Fever with low white blood cell count
Fever with low white blood cell count
1,545 reports
- Fever
Fever
1,490 reports
- Lung infection
Lung infection
1,448 reports
- Pain in your head
Pain in your head
1,355 reports
- Discomfort
Discomfort
1,301 reports
- Skin eruption
Skin eruption
1,241 reports
- Low white blood cell count
Low white blood cell count
1,150 reports
What this shows Bars show how often each reaction was reported, not how likely it is to happen, a report records a temporal association, never proof that the drug caused it.
Reports over time
Adverse-event reports filed for valacyclovir each year to the FDA Adverse Event Reporting System (FAERS).
Year-to-year volume tracks usage, prescribing, and scrutiny, not a change in per-patient risk. Source: FDA FAERS.
Where valacyclovir sits
valacyclovir has more FDA adverse-event reports than 69% of the drugs FAERS tracks. A high position reflects how widely a drug is used and watched, not how dangerous it is.
Percentile across all drugs PlainMeds tracks by FAERS report volume. The dot is valacyclovir; the line is the median (50th percentile).
FDA Adverse Event Report Analysis
Detailed analysis of 39,048 reports from the FDA Adverse Event Reporting System (FAERS). Reports span 2004–2025.
Total Reports
39,048
Reports Mentioning Death
3,520
9.0% of reports — not proof of cause
Hospitalization Reports
15,607
Top Indication
Product Used For Unknown Indication
Gender Distribution
Age Distribution
Most Reported Adverse Reactions (FAERS)
| # | Reaction | Reports |
|---|---|---|
| 2 | FATIGUE | 2,294 |
| 3 | DIARRHOEA | 2,120 |
| 5 | NAUSEA | 1,838 |
| 6 | FEBRILE NEUTROPENIA | 1,545 |
| 7 | PYREXIA | 1,490 |
| 8 | PNEUMONIA | 1,448 |
| 9 | HEADACHE | 1,355 |
| 10 | PAIN | 1,301 |
| 11 | RASH | 1,241 |
| 12 | NEUTROPENIA | 1,150 |
| 13 | ACUTE KIDNEY INJURY | 1,101 |
| 14 | DYSPNOEA | 1,063 |
| 15 | DEATH | 1,049 |
| 16 | ASTHENIA | 1,047 |
| 17 | COVID-19 | 1,001 |
Reactions in Death Reports
Reactions in Hospitalization Reports
Source: FDA FAERS (Adverse Event Reporting System) FDA FAERS (Adverse Event Reporting System) Reports are voluntary and do not establish causation
Serious Warnings
Valacyclovir can cause serious problems like TTP/HUS, which is a blood disorder. This is more likely in people with advanced HIV or who have had bone marrow or kidney transplants, especially if they take high doses (8 grams per day). It can also cause kidney failure, especially in older adults or people with kidney problems. Rarely, it can cause confusion, hallucinations, or agitation. Stop taking this medicine and contact your doctor immediately if you experience any of these side effects.
Known Drug Interactions
Some examples of drugs that are eliminated by active tubular secretion include, but are not limited to, acyclovir, cidofovir, ganciclovir, valacyclovir, valganciclovir, aminoglycosides (e.g., gentamicin), and high-dose or multiple NSAIDs [see Warnings and Precautions (5.4) ] .
Mechanism: Both of these drugs are removed from the body through the same pathway in the kidneys, which may cause them to compete for exit.
What to do: Your doctor should monitor your kidney function closely while you are taking both medications.
Some examples include, but are not limited to, acyclovir, adefovir dipivoxil, cidofovir, ganciclovir, valacyclovir, valganciclovir, aminoglycosides (e.g., gentamicin), and high-dose or multiple NSAIDs [see Warnings and Precautions (5.3) ] .
Mechanism: Both of these drugs are removed from the body through the kidneys, and taking them together can increase the risk of kidney damage.
What to do: Your doctor should monitor your kidney function closely while you are taking both of these medications.
Some examples include, but are not limited to, acyclovir, cidofovir, ganciclovir, valacyclovir, valganciclovir, aminoglycosides (e.g., gentamicin), and high-dose or multiple NSAIDs [see Warnings and Precautions ( 5.2)].
Mechanism: Both of these drugs are removed from the body by the kidneys, and taking them together can put extra stress on your kidney function.
What to do: Your doctor should check your kidney function regularly while you are using these medications together.
This is a plain-language summary of interactions documented in FDA labeling, not individualized advice. Ask a pharmacist or prescriber before combining medications.
Common Questions
Can I take valacyclovir if I'm allergic to acyclovir?
How quickly does valacyclovir work?
Can valacyclovir cure herpes?
Does valacyclovir interact with other medications?
Can children take valacyclovir?
What should I do if I think I have a side effect?
Can I drink alcohol while taking valacyclovir?
How long can I take valacyclovir for suppressive therapy?
What if I have kidney problems?
Can valacyclovir prevent the spread of genital herpes?
What are the common side effects of valacyclovir?
Does valacyclovir interact with other medications?
What drug class is valacyclovir?
Is there a generic version of valacyclovir?
Is valacyclovir safe during pregnancy?
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Medication Guides
Understanding Drug Interactions
How CYP450 enzymes, inhibitors, and inducers affect your medications
Generic vs Brand Name Drugs
FDA requirements, cost savings, and when the difference matters
Narrow Therapeutic Index Drugs
Why some drugs demand precise dosing and monitoring
Common Drug Interactions
Dangerous medication combinations and how to protect yourself
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What the FDA Data Shows for valacyclovir
The FDA label for valacyclovir (sold under brand names such as Valtrex) classifies it as a prescription-only medication in the Antiviral class. Valacyclovir treats cold sores, genital herpes, and shingles. Official labeling lists 3 commonly reported side effects, including Headache, Nausea, Abdominal pain.
Post-market surveillance from the FDA Adverse Event Reporting System (FAERS) captures real-world experience. For this drug, FAERS contains 39,048 voluntary reports. The database also lists 3 documented drug interactions derived from FDA labeling, with the top-flagged interaction rated minor severity. NADAC pricing from CMS shows a generic unit cost of $0.43 versus $20.32 for the brand - a 98% generic savings.
Report counts do not establish causation, a FAERS entry documents a temporal association, not proof that the drug produced the outcome. Widely prescribed medications naturally accumulate more reports than niche therapies, so raw totals must be interpreted alongside total exposure. Shortage status, recall history, and patent information further shape supply and switching decisions. This page summarizes public FDA data for educational purposes only and is not a substitute for professional medical advice, always consult a licensed healthcare provider before starting, stopping, or changing any medication.
Data Sources
Drug labeling: FDA Drug Labels (SPL/DailyMed). Adverse events: FDA Adverse Event Reporting System (FAERS). Pricing: CMS National Average Drug Acquisition Cost (NADAC).
FAERS reports are voluntary and do not establish causation. Drug interactions are derived from FDA labeling and clinical references. Always consult a healthcare professional before making medication decisions.
Last updated: July 11, 2024
Read our methodology - how this data is sourced, computed, and verified.
Data currency: FDA FAERS adverse-event reports through 2025, CMS NADAC acquisition-cost pricing effective December 2024, compiled and last refreshed May 2026. See our methodology for per-source dates and refresh cadence. Spot a figure that looks wrong? Report a correction.
All federal data sources used on this page
- FDA Orange Book - approved drug products with therapeutic equivalence. accessdata.fda.gov/cder/ob
- FDA DailyMed - NIH-hosted drug labeling for FDA-approved meds. dailymed.nlm.nih.gov
- FDA Adverse Event Reporting System (FAERS) - post-marketing safety surveillance. fda.gov/drugs/faers
- NLM RxNorm - standardized clinical drug nomenclature. nlm.nih.gov/research/umls/rxnorm
- CMS Medicare Part B Drug Average Sales Price Files - federal drug pricing data. cms.gov/medicare/part-b-drugs/asp
- FDA Drug Shortages Database - current and resolved drug shortage tracking. accessdata.fda.gov/drugshortages