Valtrex for Cold Sores: How Long Does It Take to Work?

10/11/2025

What is Valtrex?

Valtrax is categorized as an antiviral drug that is indicated for managing a broad range of infections induced by herpes viruses, such as shingles, genital herpes, and cold sores. It aims to slow down the growth and proliferation of the herpes virus, which, in turn, allows the body to fight off the infection.

In addition to the above,  it is also prescribed to children suffering from either cold sores or chickenpox. The recommended age for using this medication for cold sores is 12 years and older, and for chicken pox, it is 2 years and older. 

This medication will not eradicate the herpes infection entirely and will not prevent you from transmitting it to other people. It just functions by reducing the severity of an infection by managing symptoms. It stops the proliferation of the viruses in the body and eliminates the infection. 

This medication may also be used for purposes not listed in this guide.

How does Valtrex work for cold sores?

As mentioned above, it is one of the most popular antiviral medications, effective against a wide range of conditions, including cold sores. It is a prescription drug that aims to improve recovery rates and diminish the severity of an outbreak. To get the maximum benefits from it, take it as soon as you experience the first symptoms of cold sores, such as itching, tingling, and burning. Let’s break down its mechanism for cold sores:

• It is a prodrug of acyclovir, which means it is converted into the active antiviral drug acyclovir in the body after administration.

• It starts functioning by preventing the herpes simplex virus from growing and spreading further, which results in cold sores.

• Valtrex helps manage symptoms and reduce the severity of an outbreak; it doesn’t cure the herpes virus. It remains dormant for years and can reappear after exposure to a trigger. 

Note: This medication delivers the best result when taken at the first symptoms of a cold sore, such as itching, burning, and tingling.

How should Valtrex be used? 

The correct use of this medication will be determined by your healthcare provider based on your current health status, medical history, and other medicines that you are taking. It is highly imperative to abide by the instructions laid down by your doctor regarding the amount and frequency of dosage.  Beginning treatment at the first signs is often recommended; if you take the medication once the blisters have fully developed, it may interfere with its effectiveness. Generally, the treatment duration with Valtrex is short when used for cold sores. The correct treatment duration will be determined by your medic based on the severity of the infection.

The correct duration depends on the infection for which you are taking it. It is prescribed to address a number of infections caused by the herpes virus. Your age, medical history, the severity of the infection, and other ongoing treatments are taken into account to determine Valtrex dosage for cold sores. Therefore, it is essential to consult a certified healthcare provider before commencing treatment. 

The valacyclovir dosage and treatment duration vary from one person to another, depending on the condition and the infection being treated.

Key information regarding Valtrex dosage for cold sores: 

Adults: the recommended dosage for adults is 2000 mg every 12 hours for one day.

Children aged 12 years and above: in children, the recommended dosage is 2000 mg every 12 hours for one day.

Children under the age of 12 years: The doctor will determine the use and dose after a careful assessment of the child's health. It will be prescribed only when the benefits outweigh the risks.

Are there any side effects of Valtrex?

Like any other medication, this medication may also result in some side effects. Side effects associated with this medication are bifurcated into two broad categories: common and serious. Common side effects tend to wear off on their own without medical intervention. In case they exacerbate or multiply, please inform your doctor immediately. You may need a dosage adjustment or a new treatment if common side effects become bothersome or start affecting your day-to-day life. The following are the common adverse effects:

• Headache

• Dizziness

• Tiredness

• Skin rash

• Stomach pain

• Nausea 

Serious side effects are reported rarely, but they can’t be eliminated entirely. Therefore, if you come across any serious side effects mentioned below, get immediate medical attention. 

• Easy bruising or bleeding

• Severe allergic reactions

• Mental or mood changes

• Kidney problems

• Thrombotic thrombocytopenic purpura/haemolytic uremic syndrome

Precautions to keep in mind while taking Valtrex:

Before you start the consumption of this medication for any purpose, make sure to have a look at the precautions that you should follow while on this medication. These preventive measures will enable you to reap the most benefits and minimize your risk of encountering unwanted complications.

• If you show an allergy to the active or inactive ingredients present in this medication, kindly refrain from its consumption. If taken despite being allergic to it, you are likely to experience a severe allergic reaction, which can be fatal sometimes.

• This medication is not a cure for chickenpox, shingles, genital herpes, or cold sores. It just functions by managing symptoms and eliminating infection. If you are using it for genital herpes, it is important to practice safe sex, or it may be passed to your sexual partner.

• While using this medication, drink plenty of fluids to prevent dehydration. People aged 65 and above are at high risk of developing some side effects from this medication. The doctor may adjust valacyclovir dosage if you fall under this age group.

• If you are unable to swallow a tablet, you can ask your pharmacist to make the liquid form of this medication. If you opt for this form, please keep it refrigerated between 36°F and 46°F.  Before you use it, shake it well and use a measuring spoon to measure the Valtrex dose for fever blisters or any other infection accurately.

• If you are either pregnant or a breastfeeding mother, please consult your doctor before you use it. The doctor will inform you of the associated risks and benefits of consuming this medication during these phases.

The takeaway:

Cold sores are tiny fluid-filled blisters on and around the lips that affect a significant portion of the population. They are highly contagious and can reactivate later after coming into contact with a trigger, such as stress, sunlight, hormonal changes, or fever. However, breakthroughs like Valtrex have made it easier to treat cold sores and reduce their severity. Valtrex is a brand-name medication for its generic equivalent, valacyclovir, which is used to manage a broad range of infections caused by the herpes virus, including cold sores. It is one of the most recommended antivirals for cold sores, genital herpes, and shingles, and is often recommended to take at the first sign of an outbreak. Most people start noticing improvement with the use of Valtrex within 2 to 3 days, but complete results may take 10 days or longer to appear. To reap the most benefits, you should take it as soon as you notice the first symptoms; the earlier you start, the better the outcome. If the infection reappears, you need to start the treatment as early as possible to heal within 4 to 5 days.