valacyclovir
Brand names: Valtrex
Valacyclovir is an antiviral medicine. It is used to treat infections caused by certain viruses.
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.
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.
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.
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.
Storage
Store valacyclovir tablets at room temperature, away from heat and moisture.
Side Effects (from patient reports)
Based on 17,827 FDA adverse event reports.
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
Death-Related Reports
3,520
Hospitalization Reports
15,607
Top Indication
Product Used For Unknown Indication
Gender Distribution
Age Distribution
Most Reported Adverse Reactions (FAERS)
| # | Reaction | Reports |
|---|---|---|
| 1 | OFF LABEL USE | 2,544 |
| 2 | FATIGUE | 2,294 |
| 3 | DIARRHOEA | 2,120 |
| 4 | DRUG INEFFECTIVE | 1,892 |
| 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 |
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.
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?
Related Medications in Antiviral
Other drugs grouped near valacyclovir — same-class peers and common alternatives.
acyclovir
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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
Related Health & Safety Data
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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 17,827 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.
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