Acyclovir
Acyclovir · Say it: a-SY-kloh-vir
Acyclovir is a prescription antiviral tablet taken by mouth to treat shingles, genital herpes, and chickenpox.
Brand names: Zovirax
Used for
Acute treatment of herpes zoster (shingles)
Comes as
400 mg tablets: pink, shield-shaped, flat tablets; 800 mg tablets: blue, oval, biconvex tablets
Common side effects
Nausea and/or vomiting, Diarrhea, Headache
| Generic name | Acyclovir |
|---|---|
| Brand names | Zovirax |
| Type of medicine | An antiviral medicine of the nucleoside analogue type, used against herpesviruses |
| How it is sold | Prescription antiviral tablet |
| Comes as | 400 mg tablets: pink, shield-shaped, flat tablets; 800 mg tablets: blue, oval, biconvex tablets |
| Route | oral |
| Boxed warning | No |
| Label date | 2026-02-02 |
💊 What is Acyclovir used for?
- Acute treatment of herpes zoster (shingles)
- Treatment of initial episodes and management of recurrent episodes of genital herpes
- Treatment of chickenpox (varicella)
How it works
The label describes acyclovir as a synthetic nucleoside analogue that is active against herpesviruses. The label does not explain its action in more detail.
How it is usually taken
- Acyclovir is taken by mouth and is for oral use only. It is taken several times a day, at regular intervals, for a set number of days. The label says the schedule depends on the condition being treated, and some people take it long term to help prevent recurrent genital herpes. Follow the instructions from your prescriber or pharmacist. The label also says to maintain adequate hydration.
Comes as
- 400 mg tablets: pink, shield-shaped, flat tablets
- 800 mg tablets: blue, oval, biconvex tablets
⚠️ Acyclovir side effects
Common side effects
- Nausea and/or vomiting
- Diarrhea
- Headache
- Malaise (a general feeling of being unwell)
- Pain
- Fever
- Dizziness
- Rash, itching, or hair loss (less common, reported after the medicine was approved)
Get medical help right away if
- Get medical help right away if you develop a painful rash, especially one that involves the mouth, eyes, or other mucous membranes. The label says to stop taking acyclovir and seek medical attention.
- Contact your healthcare provider right away if you develop any rash. The label says severe skin reactions have been reported, including Stevens-Johnson syndrome, toxic epidermal necrolysis, drug reaction with eosinophilia and systemic symptoms (DRESS), and erythema multiforme.
- Get medical help right away if a rash becomes progressive or severe. The label says to stop the medicine in this case.
- Tell your prescriber right away about severe or troublesome side effects. The label notes that kidney failure, sometimes fatal, has been seen with acyclovir.
- Tell your prescriber right away if you notice confusion, agitation, hallucinations, seizures, tremors, or unusual drowsiness. The label lists these nervous system effects and says they may be marked, especially in older adults or people with kidney problems.
- The label also lists TTP/HUS, which has caused deaths in immunocompromised patients, and liver-related problems such as jaundice and hepatitis.
🛑 Who should not take Acyclovir, and who should be careful
The label says not to take it if
- You have had a clinically significant allergic-type reaction to acyclovir, valacyclovir, or any ingredient in the tablet. The label lists examples such as anaphylaxis and severe skin reactions.
- You have developed a severe skin reaction (SCAR) after using acyclovir or valacyclovir. The label says the tablets are contraindicated in this case.
Tell your doctor before taking it if
- Tell your prescriber if you have kidney problems. The label says the dose may need to be adjusted for people with kidney impairment, including those on hemodialysis.
- Tell your prescriber if you take other medicines that may harm the kidneys. The label says caution is needed with these.
- Tell your prescriber if you are pregnant, may become pregnant, or plan to breastfeed.
- Tell your prescriber if you have a history of a severe skin reaction to acyclovir or valacyclovir.
- The label says acyclovir is not a cure for genital herpes and does not show whether it prevents spreading the infection to others.
🔀 Acyclovir with other medicines, food and alcohol
The label says to discuss these with your doctor or pharmacist
- The label refers to another section for drug interactions, and that section is not included here. The label says caution is needed when acyclovir is given with potentially nephrotoxic agents (medicines that may harm the kidneys), since this may raise the risk of kidney problems and reversible nervous system symptoms. Tell your pharmacist about all medicines you take.
Alcohol and food
The label does not give specific guidance about taking acyclovir with food or about alcohol. It says to maintain adequate hydration.
🤰 Acyclovir in pregnancy and breastfeeding
Pregnancy
The label lists this as Pregnancy Category B. In animal studies, acyclovir was not shown to cause birth defects, but there are no adequate and well-controlled studies in pregnant women. A pregnancy registry included 749 pregnancies exposed during the first trimester, and the birth defect rate looked similar to the general population, but the registry was too small to draw firm conclusions. The label says acyclovir should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.
Breastfeeding
The label says acyclovir has been measured in breast milk in 2 women. It says the medicine should be given to a nursing mother with caution and only when indicated.
🗓️ Storage, missed doses and taking too much
Storage
Store between 15 and 25 degrees Celsius. Protect from light and moisture.
If a dose is missed
The label does not say.
If too much is taken
The label says overdoses involving up to 100 capsules (20 g) have been reported. Reported effects include agitation, coma, seizures, and lethargy. Overdose can also lead to kidney problems, including kidney failure. The label says hemodialysis may help in cases of acute renal failure and anuria. Seek medical help right away if an overdose is suspected.
🗒️ Questions to ask about Acyclovir
🎯 Check what you understood
1. According to the label, what is acyclovir used to treat?
2. What does the label say to do if a painful rash with mucosal involvement develops?
3. According to the label, is acyclovir a cure for genital herpes?
❓ Acyclovir: frequently asked questions
Is acyclovir a cure for genital herpes?
No. The label says patients should be informed that acyclovir tablets are not a cure for genital herpes. It also says there is no data showing whether acyclovir prevents transmission to others.
What should I do if I get a rash while taking acyclovir?
The label says to immediately contact your healthcare provider if you develop a rash. If a painful rash with mucosal involvement develops, the label says to stop taking acyclovir and seek medical attention right away.
Can acyclovir be used during pregnancy?
The label says there are no adequate and well-controlled studies in pregnant women. It says acyclovir should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus, so talk with your prescriber.
Does acyclovir pass into breast milk?
The label says acyclovir has been found in breast milk in 2 women. It says the medicine should be given to a nursing mother with caution and only when indicated.
What should I do if I think someone has taken too much acyclovir?
The label reports that overdoses have caused agitation, coma, seizures, lethargy, and kidney problems. It says hemodialysis may help in acute renal failure. Seek medical help right away.
🧪 Tests and reports linked to Acyclovir
The label text mentions these. If you have one of these reports, get every line of it explained.
- Kidney function tests
a test or report linked to this medicine
- Metabolic panel (BMP, CMP)
a test or report linked to this medicine
- Culture and sensitivity
a test or report linked to this medicine
- Urinalysis
a test or report linked to this medicine
- Hepatitis panel
a test or report linked to this medicine
- Pregnancy hCG test
a test or report linked to this medicine
📖 Medical words used on this page
- Acute vs chronic
Acute means something started recently or suddenly. Chronic means it has lasted a long time or keeps coming back.
- Anaphylaxis
Anaphylaxis is a severe, whole-body allergic reaction that comes on fast and is a medical emergency needing urgent help.
- Antiviral
An antiviral is a medicine that works against viruses, stopping them from multiplying. Different antivirals work against different viruses.
- Anuria
Anuria means the body is making no urine, or almost none. It is a serious sign, usually of kidney failure or a blockage, and needs urgent medical help.
- Congenital malformations
Congenital malformations are differences in the structure of the body that are present at birth, such as heart, spine or lip and palate defects.
- Contraindication
A contraindication is a reason not to use a particular medicine, test or procedure for a person because it could cause harm.
- Hemodialysis
Hemodialysis is a treatment where a machine filters the blood to remove waste and extra fluid when the kidneys cannot do it well enough.
- Hepatic
Hepatic simply means 'to do with the liver', as in hepatic impairment (reduced liver function) or hepatic enzymes.
- Hepatitis
Hepatitis means inflammation of the liver. It can be caused by viruses, alcohol, some medicines or the immune system.
- Herpesviruses
Herpesviruses are a family of viruses that stay in the body for life after infection, including those that cause cold sores, genital herpes and chickenpox.
- Hypertension
Hypertension means high blood pressure: the force of blood against artery walls stays higher than it should over time.
- Immunocompromised
Immunocompromised describes a person whose immune system is weaker than usual, from illness or medicines, so they get infections more easily.
- Immunosuppression
Immunosuppression means the immune system is working less strongly than usual, either because of a medicine or an illness, so infections are more likely.
- Impression
The impression is the summary at the end of a scan report, where the radiologist gives the main conclusions.
📖 Medical words on this page
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Explain my leafletDecode my prescription🔗 Trusted sources about Acyclovir
- Full official label on DailyMed ↗
US National Library of Medicine: the complete FDA label this page is based on
- Acyclovir on MedlinePlus ↗
US National Library of Medicine's patient drug information
- Search the NHS website for Acyclovir ↗
UK National Health Service
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- Report a side effect in the US (FDA MedWatch) ↗
- Report a side effect in the UK (Yellow Card) ↗
- FDA recalls and safety alerts ↗
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Source: official FDA drug label (label updated 2026-02-02). Read the full label on DailyMed
MedicDecode explains the official label in plain words. It is not medical advice and does not replace your doctor or pharmacist. Never start, stop or change a medicine because of what you read here.