Valtrex, also known as Valacyclovir, is a medication used to treat cold sores. It works by preventing the virus from multiplying, helping your body fight the infection more effectively.

While Valtrex can be incredibly effective in treating this condition, there are potential side effects of Valtrex for cold sores that all patients should be aware of. Let’s take a closer look at what Valtrex is and the possible side effects associated with it. 

What is Valtrex? 

Valtrex (Valacyclovir Hydrochloride) is an antiviral medication used to treat infections caused by certain viruses such as the Herpes Simplex Virus Type 1 (HSV-1), which causes cold sores, and type 2 (HSV-2), which causes genital herpes.

It belongs to a class of drugs known as nucleoside analogs and works by preventing the growth of viral cells. This means that when taken regularly, Valtrex can help reduce the severity of your symptoms and the frequency of outbreaks. 

You can also check our article on Can You Use Clindamycin for Cold Sores?

Valtrex for Cold Sores 

Cold sores are caused by HSV-1 and can appear on or around your lips or mouth. While they are highly contagious, they can also be treated with Valtrex. Using Valtrex to treat cold sores can reduce healing time by up to two days and prevent future outbreaks from occurring.

It is also important to note that using Valtrex can help prevent transmission of HSV-1 to other parts of your body or even to other people who come in contact with you during an outbreak. 

Common Side Effects of Valtrex


Headaches are one of the most commonly reported side effects of taking Valtrex for cold sores. This is typically caused by the body adjusting to the new medication and should subside within a few days of starting treatment with Valtrex.

In rare cases, however, headaches may persist or become worse over time and should be discussed with your doctor if they become unmanageable or interfere with your normal activities. 


Nausea is another common side effect experienced when taking Valtrex for cold sores. Nausea is usually mild and can typically be managed by drinking plenty of fluids and avoiding foods that may trigger further nausea or vomiting.

If nausea persists or becomes severe, speak with your doctor as soon as possible, as this could be an indication of an allergic reaction to the medication, which requires immediate medical attention. 

Other Common Side Effects 

In addition to headaches and nausea, other common side effects associated with taking Valtrex for cold sores include dizziness, drowsiness, fatigue, muscle aches, rashes, and stomach pain.

These symptoms should subside on their own after a few days, but it’s important to monitor them closely and speak with your doctor right away if they become worse or persist over time.  

Serious Side Effects of Valtrex

Kidney Failure

Valtrex has been linked to rare cases of kidney failure. Symptoms such as changes in urine output or color, decreased urination, swelling or pain in the abdomen, and an inability to urinate can all indicate kidney failure.

If you experience any of these symptoms while taking Valtrex, contact your doctor immediately. 

Nervous System Problems

Nervous system problems can also occur with the use of Valtrex. These include seizures, confusion, trouble concentrating or thinking clearly, depression or other mood changes, weak or clumsy movements, numbness or tingling in the arms or legs, and loss of coordination.

If you experience any such symptoms while taking Valtrex, then contact your doctor right away. 

Other Serious Side Effects H3

In addition to kidney failure and nervous system problems, other serious side effects have been reported with the use of Valtrex, including liver damage and blood disorders such as thrombocytopenia (low platelet count) and anemia (low red blood cell count).

If you experience any signs of abnormal bleeding while taking this medication, then speak with your doctor right away. 

Valtrex Warnings

Underlying Health Conditions

Before taking Valtrex for a cold sore outbreak, it is important to discuss any underlying health conditions with your doctor. People who have kidney or liver problems should not take Valtrex or use it with caution, as these conditions may affect how the body processes the medicine.

Additionally, people who have HIV/AIDS or certain other immune system issues should also use caution when taking this drug, as they may be at an increased risk of developing serious side effects. 

Age Restrictions

Valtrex is not recommended for children under 12 years old unless advised by a doctor. The safety and efficacy of this medication has not been established in children under 12 years old.

So parents should consult a doctor before giving their child Valtrex. For adults over 65 years old, lower doses may be prescribed due to age-related kidney problems that can affect how the body processes the medication. 

Pregnancy and Breastfeeding

Valtrex should only be used during pregnancy if absolutely necessary, as there are risks associated with taking this drug while pregnant. Women who are pregnant or planning on becoming pregnant should consult their doctor before using Valtrex for cold sores or any other condition.

Additionally, women who are breastfeeding should speak to their doctor before using this drug as it could pass into breast milk and cause harm to the infant’s health.  

Interactions with Other Medications 

Before taking Valtrex for your cold sore outbreak, it’s important to make sure that it won’t interact negatively with any other medications you may be taking. This includes supplements like vitamins and minerals as well as prescription medications such as blood thinners or immunosuppressants.

If you are already taking any of these medications or supplements, make sure to talk to your doctor before starting Valtrex treatment so they can evaluate any potential interactions between the two drugs or supplements. 

How to Avoid Valtrex Side Effects?

Take the Right Dose at the Right Time of Day

The most important thing to remember when taking any type of medication is to follow the dosage instructions from your doctor or pharmacist. If you take too much, it could lead to serious side effects.

Taking Valtrex at the same time each day will also help ensure that your body gets used to the medication and that you don’t experience any adverse reactions. 

Take Valtrex with a Full Glass of Water

It’s important to always take Valtrex with a full glass of water. Not only will this help the medication absorb better into your system, but it will also help flush out any unwanted toxins that could cause unpleasant side effects like headaches or nausea.

Be sure to drink plenty of liquids throughout the day while taking Valtrex—water is best, but other fluids like juice or tea are fine as well. 

Switch Medications if Necessary

If you start experiencing severe side effects from Valtrex, talk to your doctor about switching medications or adjusting your dose. There are many different types of antivirals available on the market, so there are plenty of options if something isn’t working for you.

Your doctor can work with you to find a treatment plan that works best for you and minimize any potential side effects that you may experience while taking Valtrex. 

Do not Take more than the Prescribed Dose of Valtrex

It’s never a good idea to take more than the prescribed dose of any type of medication, including Valtrex. Doing so could lead to serious health risks, so make sure you stick strictly to what your doctor has recommended for you.

If in doubt, always check with your healthcare provider before increasing your dose or changing anything about how often or how much you’re taking.  

Tell your Doctor about Any Allergies or Medical Conditions you have

Before starting on any new medication, it’s important that your doctor knows about any allergies or medical conditions that you have in order to avoid potential complications from drug interactions or allergic reactions.

Make sure they know everything about your medical history before beginning treatment with Valtrex so they can decide if it’s safe for use and adjust your dosage accordingly if necessary.  

Ask questions if you don’t Understand Something

Don’t be afraid to ask questions if something doesn’t make sense when reading through information about taking Valtrex—or anything else related to medicine! It’s better to ask now than end up dealing with unexpected consequences down the line due to not understanding something correctly in the first place.  


Valtrex is a powerful antiviral medication that can help treat and prevent outbreaks of cold sores. However, it’s important to be aware of the side effects that you may experience while taking Valtrex—as well as how to minimize them—so you can stay healthy and feel your best during treatment.

By following the right dosage instructions and talking to your doctor about any allergies or medical conditions you have, you can ensure that taking Valtrex is a safe and effective experience. 

We hope that this article has provided you with the information you need to understand the side effects of Valtrex for cold sores and how to minimize them. If you have any questions or concerns, don’t hesitate to speak with your doctor. Until then, take care of yourself and stay safe!