How Effective Is Valacyclovir for Cold Sores?

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  • Written By: Jennifer Voight
  • Edited By: Melissa Wiley
  • Last Modified Date: 29 September 2019
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Taking valacyclovir for cold sores at the first sign of infection can prevent cold sores from forming, lessen symptoms, and shorten the duration of healing time. Valacyclovir is one of the two most commonly prescribed oral medications for prevention and treatment of cold sores because of its effectiveness and low incidence of side effects. The key to maximizing the effectiveness of valacyclovir when treating cold sores is to take the drug at the earliest sign of infection, which is usually a tingling sensation referred to as the prodrome stage. Even if taken in later stages of infection, taking valacyclovir can still help by hastening healing time.

Cold sores are caused by a viral infection of the herpes simplex virus (HSV). After the infection heals, the virus takes residence within the body’s nervous system and lies dormant until the next time the immune system is weak enough to allow infection. There is no cure for HSV. Taking valacyclovir for cold sores can effectively treat the virus that is currently attacking the body's cells. It cannot fight the inactive form of the virus that lies dormant within nerve cells.


Valacyclovir is considered a prodrug. This means that the medication is not a drug in itself, but is designed to increase the bioavailability of acyclovir in the body to treat HSV. Although acyclovir can be prescribed on its own, it is not as effective as valacyclovir for cold sores because it is not as effectively used by the body. Valacyclovir is also effective longer and can be taken in smaller doses than acyclovir, therefore causing fewer side effects than acyclovir.

Repeated research studies have shown valacyclovir to shorten the duration of cold sores by one day when a dose is taken twice a day, 12 hours apart for one day. These results are considered statistically significant. Taking valacyclovir for cold sores can also lessen the amount of virus shed during active infection, making cold sores less contagious to others.

For frequent infections, valacyclovir can effectively prevent cold sores from occurring when taken daily as a preventive treatment. Depending on the severity of infections and the health of the patient, doctors may prescribe valacyclovir once or twice each day. It should be noted that long-term usage needs further study to ensure that it is safe. High levels of acyclovir in the body can cause kidney damage, so there is a possibility that valacyclovir can cause similar damage if taken long term, especially in a patient who has a compromised immune system.


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Post 3

@literally45-- You can actually prevent a cold sore with valacyclovir if you take it during the first stage -- so when there is only some itching and tingling on the lip. I don't think the medication will do anything if you have one that has already ulcerated.

The effectiveness of the medication also varies from person to person. It works for me, but it does nothing for my husband.

Post 2

@literally45-- I take valacyclovir when I feel a cold sore coming on. It doesn't just make the cold sore disappear but it makes it heal faster. If I didn't take the medication, it would take two to three weeks total for the cold sore to go away. With the medication, it's gone in a week or less.

I don't think it's a good idea to take valacyclovir all the time, unless you are constantly dealing with breakouts. Antivirals can weaken the body's immune system when they are used for a long time. I've never heard of anyone with herpes simplex type 1 take valacyclovir on a regular basis. Those with type 2 usually take them regularly.

Post 1

I get cold sores several times a year and they always occur in winter. Should I take valacyclovir throughout winter to prevent them or only when I feel one coming on? Is the medication effective when it's taken when the cold sore has already formed?

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