References UK clinical guidance from the NHS, the British HIV Association (BHIVA), and the British Association for Sexual Health and HIV (BASHH). Last updated: April 2026.
Aciclovir (also spelled acyclovir) is an antiviral medication used to treat herpes simplex (genital herpes and cold sores), shingles and chickenpox. It was the first effective antiviral for herpes and remains widely used. Available as tablets, cream and intravenous formulation, it works by stopping the herpes virus from replicating.
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Uses
| Condition | Typical Dose |
|---|---|
| Genital herpes (first episode) | 400mg three times daily for 5-10 days |
| Genital herpes (recurrence) | 800mg three times daily for 2 days |
| Suppressive therapy | 400mg twice daily |
| Cold sores (cream) | Apply 5 times daily for 5 days |
| Shingles | 800mg five times daily for 7 days |
How It Works
- Blocks viral DNA replication
- Only active in infected cells
- Reduces outbreak severity and duration
- Doesn’t cure the infection
Side Effects
- Generally very well tolerated
- Nausea
- Headache
- Stay hydrated
Aciclovir vs Valaciclovir
- Aciclovir: needs more frequent dosing
- Valaciclovir: better absorption, fewer doses
- Both equally effective
Read more: What is herpes? | Valaciclovir | Famvir
Frequently Asked Questions
Is aciclovir cream available without prescription?
Yes — cold sore cream is available from pharmacies.
Can I take it in pregnancy?
Generally considered safe — discuss with your doctor.
How quickly does it work?
Best started within 72 hours of outbreak; works faster the sooner you start.
Related reading
- Can You Get Herpes From a Toilet Seat?
- Can You Get Herpes From Kissing?
- Comprehensive Test: Chlamydia, Gonorrhoea and Herpes
- Cold Sores vs Syphilis Sores: How to Tell the Difference
- Genital Warts vs Herpes: What's the Difference?
Sources
- NHS — Sexual health conditions
- BASHH — UK clinical guidelines for STI management
- British HIV Association (BHIVA) — HIV treatment guidelines
- Terrence Higgins Trust — sexual health information
- UK Health Security Agency — STI surveillance data
Steve Page is a recognised expert on Sexually Transmitted Diseases (STDs) and STD treatments, having published numerous articles in peer-reviewed journals and presented his research at conferences around the world. He has an in-depth understanding of the latest medical research on STDs, and is an advocate for the development of new treatments and protocols to improve the health of those affected. In addition to his research, he has dedicated his career to understanding the causes and symptoms of STDs, as well as how to best treat those impacted.
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