Prescription medication · Antiviral (Nucleoside Analog)
acyclovir
Also sold as Zovirax. Acyclovir is used to treat shingles, which is caused by herpes zoster.
Data updated 2026-05-15
- 109,698
- FDA reportsOften reported
- 7
- InteractionsFew interactions
- 99% less
- Generic vs brandHuge savings
- 2
- Recall records
What the data shows
acyclovir (Zovirax) is a prescription Antiviral (Nucleoside Analog), more reported than most tracked drugs (109,698 FDA reports), whose generic costs a fraction of the brand (about 99% 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.
acyclovir (Zovirax) is a prescription Antiviral (Nucleoside Analog). Acyclovir is used to treat shingles, which is caused by herpes zoster.
Acyclovir 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
$38.30/unit
Generic Price
$0.08/unit
Generic Savings
99%
Generic Available
Yes (43 manufacturers)
Pricing data from NADAC (CMS), effective December 18, 2024. Compare all drug costs →
What it does
Acyclovir is used to treat shingles, which is caused by herpes zoster.
Common side effects
Malaise (feeling unwell), Nausea, Diarrhea
Key warnings
Acyclovir can cause nervous system problems, especially in older adults or people with kidney problems.
The sections below are summarized in plain English from acyclovir's FDA-approved prescribing information. They describe what the official label says, and are not personal medical advice.
How It Works
Acyclovir stops the virus from growing and spreading. It does this by interfering with the virus's ability to make copies of itself. This helps your body fight off the infection.
Side Effects (from patient reports)
Based on 109,698 FDA adverse event reports.
Most-reported reactions
Adverse reactions in FAERS for acyclovir, by number of reports
- Fatigue
Fatigue
7,612 reports
- Diarrhoea
Diarrhoea
7,064 reports
- Pneumonia
Pneumonia
5,471 reports
- Nausea
Nausea
5,328 reports
- Pyrexia
Pyrexia
4,719 reports
- Death
Death
4,676 reports
- Rash
Rash
4,121 reports
- Dyspnoea
Dyspnoea
3,452 reports
- Asthenia
Asthenia
3,193 reports
- White Blood Cell Count Decreased
White Blood Cell Count Decreased
3,088 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 acyclovir 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 acyclovir sits
acyclovir has more FDA adverse-event reports than 87% 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 acyclovir; the line is the median (50th percentile).
FDA Adverse Event Report Analysis
Detailed analysis of 109,698 reports from the FDA Adverse Event Reporting System (FAERS). Reports span 2003–2025.
Total Reports
109,698
Reports Mentioning Death
13,944
12.7% of reports — not proof of cause
Hospitalization Reports
40,651
Top Indication
Product Used For Unknown Indication
Gender Distribution
Age Distribution
Most Reported Adverse Reactions (FAERS)
| # | Reaction | Reports |
|---|---|---|
| 1 | FATIGUE | 7,612 |
| 2 | DIARRHOEA | 7,064 |
| 4 | PNEUMONIA | 5,471 |
| 5 | NAUSEA | 5,328 |
| 6 | PYREXIA | 4,719 |
| 7 | DEATH | 4,676 |
| 9 | RASH | 4,121 |
| 10 | DYSPNOEA | 3,452 |
| 11 | ASTHENIA | 3,193 |
| 12 | WHITE BLOOD CELL COUNT DECREASED | 3,088 |
| 13 | HEADACHE | 3,080 |
| 14 | NEUTROPENIA | 3,074 |
| 15 | PLATELET COUNT DECREASED | 2,964 |
| 16 | CONSTIPATION | 2,832 |
| 17 | VOMITING | 2,798 |
Reactions in Death Reports
Reactions in Hospitalization Reports
Source: FDA FAERS (Adverse Event Reporting System) Reports are voluntary and do not establish causation
Serious Warnings
Acyclovir can cause nervous system problems, especially in older adults or people with kidney problems. Tell your doctor if you have kidney problems before taking this medicine.
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: These medications leave the body through the same kidney filters, which could lead to a buildup of the drugs in your system.
Drug Interactions Probenecid Probenecid is known to interact with the metabolism or renal tubular excretion of many drugs (e.g., acetaminophen, acyclovir, angiotensin-converting enzyme inhibitors, aminosalicylic acid, barbiturates, benzodiazepines, bumetanide, clofibrate, methotrexate, famotidine, furosemide, nonsteroidal anti-inflammatory agents, theophylline, and zidovudine).
Mechanism: Probenecid is given with cidofovir and can slow down the removal of acyclovir through the kidneys. This can lead to an increase in the amount of acyclovir in your blood.
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: These medicines are cleared from the body using the same pathway in the kidneys, which can lead to higher levels of the drugs in your system.
Acyclovir Clinical Impact: The concomitant use of acyclovir may increase the plasma concentrations of meperidine and its metabolite, normeperidine. Intervention: If concomitant use of acyclovir and Meperidine Hydrochloride Tablets or Oral Solution is necessary, evaluate patients for respiratory depression and sedation at frequent intervals.
Mechanism: Acyclovir can cause meperidine and its breakdown products to build up in your blood. This makes the drug's effects stronger and more likely to cause side effects.
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: These two drugs are both filtered out of the body by the kidneys, which can increase the risk of kidney strain when used at the same time.
This is a plain-language summary of FDA-label interaction records and does not provide individual medication-combination directions.
Common Questions
Can I drive while taking acyclovir?
How long does it take for acyclovir to work?
Can I drink alcohol while taking acyclovir?
What should I do if I have side effects?
Can I get a refill of acyclovir if I have some left over?
Is acyclovir safe for children?
Can acyclovir cure herpes?
Does acyclovir interact with other medications?
What does acyclovir look like?
What if I can't swallow pills?
What are the common side effects of acyclovir?
Does acyclovir interact with other medications?
What drug class is acyclovir?
Is there a generic version of acyclovir?
What pregnancy or breastfeeding source fields are listed for acyclovir?
Has acyclovir been recalled?
Active Recalls
Lack of Assurance of Sterility
Fresenius Kabi Compounding, LLC
Presence of Particulate Matter: Customer complaint of dark particles found inside the vial
Eugia US LLC
Related Medications in Antiviral (Nucleoside Analog)
Other drugs grouped near acyclovir - same-class peers and common alternatives.
albendazole
Albenza
Albendazole is a medicine that fights parasites.
Compare with acyclovir →
amphotericin B
Ambisome, Fungizone
Amphotericin B liposome is an antifungal medicine.
Compare with acyclovir →
anidulafungin
Eraxis
Eraxis is an antifungal medicine.
Compare with acyclovir →
atovaquone/proguanil
Malarone
Malarone is a drug used to prevent and treat malaria.
Compare with acyclovir →
baloxavir marboxil
Xofluza
Xofluza is an antiviral medicine that can treat the flu.
Compare with acyclovir →
Compare beyond drug class
Nationwide peers by FAERS volume & death-report share
Two PlainMeds-derived comparison paths for acyclovir: nearest FDA FAERS report volume and nearest death-report share among drugs with at least 1,000 logged reports, excluding same-class neighbors listed above. Counts reflect reporting volume, not proven individual harm.
Similar FAERS report volume
Nearest drugs by total FAERS reports. This record: 109,698.
- famotidine Δ 320 reports · H2 Receptor Antagonist 110,018reports
- potassium chloride Δ 554 reports · Electrolyte Supplement 109,144reports
- teriparatide Δ 1,559 reports · Parathyroid Hormone Analog 111,257reports
- sertraline Δ 2,500 reports · Selective Serotonin Reuptake Inhibitor (SSRI) 112,198reports
Similar death-report share
Nearest drugs by FAERS death-report share. This record: 12.71%.
- isosorbide mononitrate Δ 0.05 pts · 19,947 reports · Nitrate Vasodilator 12.66%death share
- warfarin Δ 0.06 pts · 124,873 reports · Vitamin K Antagonist (Anticoagulant) 12.77%death share
- cimetidine Δ 0.07 pts · 9,140 reports · H2 Receptor Antagonist 12.78%death share
- denosumab Δ 0.08 pts · 196,342 reports · RANK Ligand Inhibitor 12.79%death share
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
FDA bioequivalence and label-record context for narrow therapeutic index medicines
Common Drug Interactions
Dangerous medication combinations and how to protect yourself
Save on acyclovir
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What the FDA Data Shows for acyclovir
The FDA label for acyclovir (sold under brand names such as Zovirax) classifies it as a prescription-only medication in the Antiviral (Nucleoside Analog) class. Acyclovir is used to treat shingles, which is caused by herpes zoster. Official labeling lists 3 commonly reported side effects, including Malaise (feeling unwell), Nausea, Diarrhea.
Post-market surveillance from the FDA Adverse Event Reporting System (FAERS) captures real-world experience. For this drug, FAERS contains 109,698 voluntary reports. The database also lists 7 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 $0.08 versus $38.30 for the brand - a 99% 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 (currently 2 recall records on file), and patent information are separate source-record fields. This page is a public FDA/CMS registry and does not provide medical, treatment, substitution, or medication-change directions.
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. This registry does not provide medication decisions.
Last updated: September 5, 2024
PlainMeds is rendered directly from FDA openFDA/FAERS extracts, DailyMed labels, and CMS drug-pricing files, no number is typed in by an editor. FAERS counts, recalls, shortages, and price figures on this page are queried live from those federal extracts. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error. Data current as of 2026-05-15. Primary sources: openFDA / FAERS, DailyMed and CMS Part B ASP.
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 from the source snapshot dated . See our methodology for per-source dates and refresh cadence. Spot a figure that looks wrong? Report a data issue.
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