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Oral Antivirals for Cold Sores

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Topic Overview

Most cold sores heal on their own without prescription medicines. But some antiviral medicines (such as acyclovir or famciclovir) when taken orally (tablets) may be helpful in reducing the frequency and severity of attacks of cold sores.

Doctors may prescribe oral antiviral medicines that can be taken daily to prevent future outbreaks of cold sores. These medicines may also be given during periods of increased risk of getting cold sores (such as during cosmetic surgery or sun exposure).

Oral antivirals work best in treating recurring cold sores if they are taken within 24 to 48 hours of an outbreak of cold sores.

Pregnant or nursing women should seek their doctors' advice prior to taking antiviral medicines. Those with kidney problems may be advised to take lower doses.

Some examples of oral antiviral medicines prescribed to treat cold sores include the following:


Acyclovir (Zovirax) tablets may slightly shorten the duration of pain and the healing time of a first attack of cold sores.footnote 1

Common side effects of acyclovir tablets include nausea, diarrhea, and headache.

A lower dose of oral acyclovir is needed for people who have reduced kidney function.


Famciclovir (Famvir) is sometimes used to treat the herpes virus that causes cold sores and genital herpes (as well as the virus that causes shingles). This medicine is available only by prescription and is taken orally in tablet form.

If you are pregnant or nursing, you should talk with your doctor before taking famciclovir.

This medicine is not recommended for people who have had an allergic reaction to it in the past.

Possible mild side effects include itching, fever, headache, fatigue, nausea, or diarrhea.


Valacyclovir (Valtrex) capsules are available by prescription only. It is absorbed by the body much better than some other antiviral medicines (such as acyclovir).

Possible side effects include skin rash, allergic reaction, headache, dizziness, insomnia, and fatigue.

Children, pregnant women, and people who have HIV or who have had bone marrow or kidney transplants should talk with their doctors before taking this medicine.

Related Information



  1. Worrall G (2009). Herpes labialis, search date February 2009. Online version of BMJ Clinical Evidence:


ByHealthwise Staff
Primary Medical ReviewerE. Gregory Thompson, MD - Internal Medicine
Adam Husney, MD - Family Medicine

Current as ofMarch 20, 2017

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