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.
How to Take It
Take acyclovir exactly as your doctor tells you to. For shingles, the usual dose is 800 mg every 4 hours, 5 times a day for 7 to 10 days. For genital herpes, the dose is usually 200 mg every 4 hours, 5 times a day for 10 days. You can take acyclovir with or without food.
This is a plain-language summary of acyclovir'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. It is not known if acyclovir will harm an unborn baby. Talk to your doctor about the risks and benefits of taking acyclovir while breastfeeding.
This is a plain-language summary of acyclovir'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 almost time for your next dose, skip the missed dose and continue with your regular schedule.
This is a plain-language summary of acyclovir's FDA labeling, not individualized advice. Ask a pharmacist or prescriber what to do about your specific missed dose.
Storage
Store acyclovir capsules at room temperature (68° to 77°F) and keep them away from moisture.
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
- Tiredness
Tiredness
7,612 reports
- Diarrhea
Diarrhea
7,064 reports
- Lung infection
Lung infection
5,474 reports
- Feeling sick to your stomach
Feeling sick to your stomach
5,330 reports
- Fever
Fever
4,719 reports
- Death
Death
4,677 reports
- Skin rash
Skin rash
4,121 reports
- Difficulty breathing
Difficulty breathing
3,453 reports
- Weakness
Weakness
3,192 reports
- Low white blood cell count
Low white blood cell count
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) 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.
What to do: Your healthcare provider may need to check your kidney health more often while you use this combination.
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.
What to do: Your doctor may need to adjust your acyclovir dosage. Watch for any increased side effects while 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: 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.
What to do: Your doctor should check your kidney health regularly to ensure the medications are being cleared safely from your body.
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.
What to do: Your doctor should check you often for slowed breathing and extreme sleepiness.
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.
What to do: Your healthcare provider should monitor your kidney health to make sure the drugs are not causing harm.
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 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?
Is acyclovir safe during pregnancy?
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
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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 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 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: September 5, 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