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Cold sores typically occur due to a herpes simplex virus 1 (HSV-1) infection. Valacyclovir (Valtrex) makes it difficult for this virus to replicate. With replication stunted, cold sores typically go away, although the herpes virus will remain in the body. 


Valacyclovir is an oral caplet. For adults, the dosage is 2 grams twice for 1 day, taken at least 12 hours apart. It is not recommended for those under the age of 11 years. 

Side Effects

  • Headache
  • Dizziness
  • Nausea
  • Vomiting
  • Stomach pain


How long does it take for valacyclovir to work on cold sores?

One study found it to be effective in about one day. 

Can you use valacyclovir for cold sores?

It appears to be useful for cold sores, but it might not be right for everyone. A physician will make that determination. 

How much valacyclovir should I take for cold sores?

Follow the dosing instructions provided with the medication. On average, adults take two grams every 12 hours for one day. (depending upon patient the patient a physician may do more days of therapy)

Will Valtrex work after an outbreak of cold sores?

Valtrex is useful for the treatment of cold sores caused by herpes simplex or herpes zoster. Herpes simplex virus 1 (HSV-1) is the most common cause of cold sores. 

Disclaimer: this article does not constitute or replace medical advice. If you have an emergency or a serious medical question, please contact a medical professional or call 911 immediately. To see our full medical disclaimer, visit our Terms of Use page.

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