Valtrex (valacyclovir hydrochloride) is a prescription antiviral drug that can shorten the duration of cold sores, genital herpes, and shingles. It may cause mild side effects in some people.

Valtrex is available through prescription only and may cause mild side effects in some people.

This article reviews the uses, dosages, and potential side effects of Valtrex.

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The Food and Drug Administration (FDA) approved Valtrex in 2005 for the following conditions:

  • Shingles (herpes zoster): This causes a painful, itchy rash that is often on one side of the body or face that typically goes away within 2–4 weeks.
  • Genital herpes: This is a sexually transmitted infection (STI) that causes painful blisters around the genitals that can take about 2–4 weeks to heal and may flare up repeatedly throughout a person’s life.
  • Cold sores (Herpes labialis): This is an STI that is similar to genital herpes but appears around and in the mouth throughout a person’s life.

Valtrex is not a cure for cold sores. However, it may help shorten the duration of the sores and blisters during flare-ups.

Doctors do not recommend Valtrex for everyone.

For example, studies have not established Valtrex’s safety and efficacy on immunocompromised people, except for suppressing genital herpes in people with specific forms of HIV.

However, a doctor may prescribe Valtrex for people who are immunocompromised, depending on the severity of the condition.

A doctor or healthcare professional will monitor a person’s blood count while they are using this medication.

People with kidney disease should inform their doctor, who can decrease the dosage of Valtrex or recommend an alternative medication depending on the severity of the condition.

A person should talk to their doctor about their health conditions to determine whether they should take Valtrex.

For oral herpes, the National Library of Medicine (NLM) recommend a person start taking Valtrex as soon as they feel cold sore symptoms. Symptoms a person should watch for in and around the mouth include:

  • tingling
  • burning
  • itchiness

There is no clinical data to indicate that Valtrex will have any effect if a person starts taking it after blisters have formed.

A person should not take more than 1 day (2 doses) of Valtrex when treating cold sores. Take the two doses 12 hours apart. Each dose consists of 2 grams of medication.

Valtrex is an antiviral medication, which means it can help shorten the duration of cold sores.

According to Harvard Health Publishing, cold sores can last for around 10–12 days without treatment. Valtrex may reduce the formation of cold sore blisters by up to 2 days.

Valtrex may cause side effects for some people. According to the NLM, the most common side effects may include:

  • headache
  • nausea
  • abdominal pain

The most common side effect is a headache.

The NLM also state that dizziness is a common side effect in people using Valtrex for cold sores.

Other symptoms may occur when treating either shingles or herpes with Valtrex at different or prolonged doses.

The NLM state that there are no known major drug interactions between Valtrex and other medications.

There is also no known risk of taking Valtrex during pregnancy or while breastfeeding. However, the NLM acknowledge that a very small amount will be present in breast milk.

However, there are limited studies determining the medication’s adverse effects on pregnant people, such as pregnancy loss or fetal development issues.

There is a risk of accidental overdose, so a person taking Valtrex should make sure they stick to the prescribed dosage.

People living with kidney issues should talk to their doctor about their risk before taking the medication.

Valtrex is not the only prescription available for oral herpes. Famvir (famciclovir) is another antiviral medication for cold sores, shingles, and genital herpes.

It has similar side effects to Valtrex, such as headaches and nausea. Like Valtrex, people take it orally.

Prescription and nonprescription creams are available for a person to apply directly to their cold sores. Prescription-strength creams include Zovirax (acyclovir), while nonprescription creams include Abreva (docosanol).

A person typically needs to apply the cream multiple times a day to treat cold sores.

However, creams are generally less effective than oral forms of antiviral medications, such as Valtrex.

A person with kidney issues or kidney failure should ensure their doctor is aware of their situation. People with these conditions may want to ask about possible alternatives to the medication.

People who are pregnant, may become pregnant, or are breastfeeding should ask their doctor about any possible risk associated with taking Valtrex.

People living with a suppressed immune system should ask their doctor about other options.

A person should discuss any possible issues with the current medications or supplements they are taking with their doctor.

Feel free to ask the doctor about doses, how to use the medication, and whether the doctor has any special instructions.

Valtrex is a prescription antiviral medication a person can use to help shorten the duration of cold sores, genital herpes, and shingles flare-ups.

It is not a cure for cold sores. Instead, it may reduce the duration of blister flare-ups.

Valtrex is generally safe with mainly mild side effects.

However, Valtrex is one of several treatment options. Therefore, if a person has cold sores, genital herpes, or shingles, they should check with their doctor to determine the most suitable treatment for their condition.