Oral antiviral medications for prevention and treatment of cold sores

Certain antiviral medications (such as acyclovir or famciclovir) may be helpful in reducing the frequency and severity of attacks of cold sores when taken orally (tablets).1

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

Oral antivirals are most effective in treating recurring cold sores if the medications 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 medications. Those with kidney problems may be advised to take lower doses.

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


Acyclovir (Zovirax) tablets may shorten the duration of pain by 1 day and reduce the healing time of a first attack of cold sores by 1 to 2 days.1

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


Famciclovir is sometimes used to treat the herpes virus that causes cold sores and genital herpes (as well as the virus that causes shingles). Some studies show that famciclovir may work as well as acyclovir in treating cold sores.1 This medication 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 capsules are available by prescription only. Valacyclovir was approved by the U.S. Food and Drug Administration (FDA) as a 1-day treatment to reduce cold sore duration in people 12 years and older.2 It is absorbed by the body much better than some other antiviral medications (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 medication.

Most cold sores heal on their own without prescription medications or complementary therapies.


  1. Worrall G (2006). Herpes labialis, search date April 2006. Online version of BMJ Clinical Evidence. Also available online: http://www.clinicalevidence.com.
  2. Valacyclovir (Valtrex) for herpes labialis (2002). Medical Letter on Drugs and Therapeutics, 44(1143): 95–98.

Last Updated: March 13, 2008

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