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Does Valtrex work for cold sores?

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What makes Valtrex unique?When should you take Valtrex?Side effectsHow long does it take to work?Summary
Valtrex is an antiviral medication to treat infections resulting from the herpes simplex virus, such as cold sores. While it isn’t a cure, it can stop the growth of the virus.
Medically reviewed by Alisha D. Sellers, BS Pharmacy, PharmD
Written by Anisha Mansuri
Updated on

Cold sores are painful blisters that can occur on your face, most commonly around your lip area. It’s an infection resulting from the herpes simplex virus (HSV). Cold sores can be challenging to deal with as you never know how big they may get, how long they will stay, or how visible they will become.

Some over-the-counter (OTC) remedies, such as ointments and creams, may help treat cold sores. However, OTC remedies may not always work to clear the entire infection.

In this situation, a prescription antiviral medication such as Valtrex may be needed. Valtrex is the brand name of the drug valacyclovir, and it treats cold sores, as well as shingles and chickenpox.

Valtrex isn’t a cure for cold sores, and it can’t stop them from occurring in the future, but it can slow the growth of the virus enough to help your sores heal faster and shorten the duration of a flare-up. It can also decrease symptoms such as itching and pain.

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Why is Valtrex often the first choice when treating cold sores?

Small child putting lipstick on an older adult to depict avoiding sharing makeup if you are prone to cold-sores.
Elizabethsalleebauer/Getty Images

“Valtrex is often the first choice because it has better bioavailability,” says Daniel Breisch, PharmD. He’s a pharmacist at Mountain View Pharmacy in Bountiful, Utah. “That means you can take less of the drug and have superior outcomes,” he says.

Valtrex is also effective in slowing the growth and spread of HSV, which can help your immune system to better fight the infection. In addition to Valtrex, there are two other antiviral medications that can also help treat cold sores. They include acyclovir (Zovirax) and famciclovir (Famvir).

“All three have been shown to be more effective at treating cold sores than OTC creams or ointments,” says Beth Bryan, PharmD. She’s a pharmacist and the owner of Surgoinsville Pharmacy in Surgoinsville, Tennessee.

When should you take Valtrex?

If you get cold sores often, you’ll recognize the early “tingling” stage, when a sore is starting to form.

“Even if you don’t catch the infection right away, Valtrex is still highly effective if you begin taking it within 48 hours of an outbreak,” Bryan says.

The recommended dosage of Valtrex for the treatment of cold sores is 2 grams to be taken twice daily for 1 day. The doses should be taken 12 hours apart. Suppressive therapy is at a lower dose and should be taken once daily.

As Valtrex is a prescription drug, your dosage will depend on what a doctor decides is best for you.

What are the side effects of Valtrex?

“In general, Valtrex tends to be well tolerated by most people, with only minimal side effects,” says Breisch. However, common side effects can include:

Since valacyclovir is excreted through the kidneys, high doses may cause kidney damage. This is why it’s important only to take your prescribed dosage. If you miss a dose, take it as soon as you remember unless it’s almost time for your next dose, in which case you should wait to take your next one.

“Symptoms of kidney problems include an inability to pass urine, blood in the urine, or a change in how often you urinate,” explains Bryan.

“As with any medication, valacyclovir should be stopped if there are any signs of an allergic reaction, such as a rash, wheezing, chest tightness, or trouble breathing,” Bryan adds.

If you experience an allergic reaction after taking Valtrex, seek medical support immediately.

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How long does it take for Valtrex to work?

For most people, cold sores can take around 5–15 days to clear up on their own. That might sound like a short amount of time, but around 2 weeks with a large, painful sore on your lip can feel much longer.

Valtrex can reduce that time frame significantly. “Patients can feel relief in as little as a few days,” says Breisch. “In some people, it may take up to 10 days for symptoms to resolve, but it all depends on how fast you recognize the outbreak and get started on the medication.”

“Some people can get relief in just 24 hours,” mentions Bryan. The medication may be used for maintenance therapy if you have frequent outbreaks. That means you can use it for prevention, so you stop flare-ups before they occur.

If you tend to have cold sores often, it may be beneficial to discuss the potential use of Valtrex with a doctor. That way, you can have it on hand and begin taking it at the very first sign of a cold sore.


Cold sores are painful blisters that can form on your face. They are due to HSV.

OTC options, such as antiviral creams, are often the first treatments people reach for when dealing with cold sores, but they may not always get rid of the entire infection. This is where a prescription antiviral medication such as Valtrex can be effective.

Valtrex can help slow the growth and spread of HSV infections, such as cold sores, which can help the immune system fight off bacteria.

While Valtrex isn’t a cure for cold sores, it can slow the growth of the virus enough to help your sores heal faster and shorten the duration of a flare-up. It can also reduce symptoms like itching and pain.

Download the free Optum Perks Discount Card to save up to 80% on some prescription medications.

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