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Acyclovir

Brand names: Zovirax, Sitavig

Acyclovir is an antiviral that treats outbreaks of herpes viruses, including genital herpes, cold sores, shingles, and chickenpox.

Brand namesZovirax, Sitavig
Type of medicineAntiviral
Prescription?Prescription
ImportantThis page is general information, not a prescription. Don't start, stop, or change a medicine without talking to your provider or pharmacist.

Overview

It doesn't cure herpes but shortens outbreaks. It's taken more times a day than valacyclovir.

What it's used for

  • Genital herpes (outbreaks and daily prevention)
  • Cold sores
  • Shingles
  • Chickenpox in some people

How to take it

  • Start at the first sign of an outbreak.
  • Take it with or without food, spaced evenly through the day.
  • Drink plenty of fluids.

Your dose depends on your health and other medicines. Always follow your prescription label, and ask your pharmacist if anything is unclear.

Side effects

Common side effects

  • Nausea
  • Diarrhea
  • Headache
Call your provider todayConfusion, agitation, or seeing things (more likely in older adults or with kidney disease)
Call your provider todayPeeing much less
Call 911A blistering, peeling, or widespread red rash, especially with fever

Warnings

  • Doses are lower with kidney disease.
  • Shingles near the eye needs same-day care.

Other medicines, foods, and alcohol

  • Other medicines that affect the kidneys may need monitoring.

Tell your provider and pharmacist about every medicine, vitamin, and supplement you take.

Pregnancy and breastfeeding

Commonly used in pregnancy when needed.

Missed doses, overdose, and storage

If you miss a dose

Take it as soon as you remember. If it's almost time for the next dose, skip the missed one. Don't double up, and still finish the full course.

If someone takes too much

Call Poison Control at 1-800-222-1222 or get help online at poison.org. Call 911 if the person collapses, has a seizure, has trouble breathing, or can't be woken.

Storing it

Store at room temperature, away from heat and moisture (not in the bathroom), and out of reach of children and pets.

Conditions it's used for

Sources

Last updated 2026-11-13.