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Acyclovir tablets for cold sores

Dr Karen Martin
Reviewed by Dr Karen MartinReviewed on 19.10.2023 | 2 minutes read

Acyclovir is a prescription-only antiviral medicine used to treat and prevent future outbreaks of cold sores caused by the herpes simplex virus. Once you’ve had contact with the virus that causes cold sores, it lies dormant in the skin and may flare up from time to time. You might recognize triggers - stress, and exposure to the cold or sun are common ones. Acyclovir (Zovirax, Sitavig) requires a prescription.

Doctor’s advice

Who is it for?

Acyclovir helps to reduce the severity and length of an outbreak. In people with frequent outbreaks and those with a weak immune system, acyclovir tablets can be used to help reduce the number of future outbreaks as a preventative medicine. Acyclovir tablets are also used to treat outbreaks of the herpes simplex virus in other parts of the body.

When treating cold sores with acyclovir tablets, you should take your prescribed dose as soon as you recognize the tingling or burning sensation at the site of the outbreak, ideally within 5 days.

How does it work?

Acyclovir is an antiviral agent that interferes with the growth and replication of viral particles, helping your immune system to target and tackle the virus. Prescribed treatment with acyclovir is best to be used in the initial stages of an outbreak, usually within the first 5 days.

For treatment of outbreaks, you will be taking a high dose for a short course, usually for 5 days. If you are immunocompromised, treatment doses are usually double the standard doses for healthy individuals. Suppressive antiviral treatment is an option for frequent (6 or more) outbreaks causing distress or if outbreaks are affecting your social life.

Should anyone avoid taking it?

Do not take acyclovir tablets if you have previously experienced an allergic reaction to acyclovir or any ingredients used to make acyclovir tablets.

Are there any side effects?

Acyclovir is generally well-tolerated in most individuals. A small number of patients may experience symptoms of fatigue, headache, feeling dizzy, nausea, vomiting, abdominal pain, itching, and a rash (including sensitivity to light).

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This article has been written by UK-based doctors and pharmacists, so some advice may not apply to US users and some suggested treatments may not be available. For more information, please see our T&Cs.
Dr Karen Martin
Reviewed by Dr Karen Martin
Reviewed on 19.10.2023
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