AntiviralPrescription only
Aciclovir
Tablet, cream or injection
Quick Summary
Aciclovir stops herpes viruses from multiplying. It works best when started early.
Shingles
Chickenpox
Genital herpes and cold sores
Medical Uses
Shingles: Started within three days of rash.
Chickenpox: In adults or people at risk.
Genital herpes and cold sores: Outbreaks and prevention.
How it's taken
Take it as prescribed and drink plenty of water.
Your doctor decides the right dose for you and how long to take it.
Your doctor decides the right dose for you. Follow their instructions and the label.
Common Side Effects
Nausea
Diarrhoea.
Headache
Sometimes.
Kidney effects
Drink fluids to protect kidneys.
Interactions
Other kidney-affecting medicines
Increase kidney risk.
Critical Warnings
Kidney problems
Dose may need adjusting.
Confusion
Rarely, especially in older people.
Sources and further reading
Last updated 21 October 2026. For more detail, see these trusted health organisations.
- Acyclovir: drug information(opens in a new tab) · MedlinePlus, US National Library of Medicine
- Aciclovir: medicine to treat infections like cold sores, shingles, chickenpox and genital herpes(opens in a new tab) · NHS