How long after taking Valtrex are you contagious?

Valtrex minimizes the severity of cold sores and genital herpes, but does it make you less contagious?


What is Valtrex?

Valtrex (also commonly known as valacyclovir) is an antiviral medication used to treat cold sores, genital herpes, shingles, and chickenpox. Valtrex is made by GlaxoSmithKline and is the brand name for valacyclovir. Generic Valtrex is widely available.

The drug is not a cure for herpes. Instead, it is prescribed to reduce the symptoms and discomfort caused by the herpes simplex virus type 1 and 2 (HSV-1 and HSV-2), and other viral infections including chickenpox and shingles.

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How long does it take for valacyclovir to start working?

The amount of time it takes for Valtrex to begin working usually depends on the severity of your symptoms and when you started your treatment.

At a standard dose of 1g twice a day, valacyclovir acts rapidly and you should notice some relief within 48 hours. If your herpes outbreak is severe, it could take a little longer for Valtrex to stop HSV from replicating. 


If you are having your first herpes outbreak, take Valtrex within 48 hours after symptoms occur. Depending on the severity, your doctor may recommend a dose of 1g once or twice a day for up to 10 days.

It can take up to 10 days for herpes sores and blisters to heal fully, which makes it all the more important to take Valtrex as soon as symptoms occur.


Follow your doctor’s advice and take Valtrex for as long as prescribed.


Once a person is a carrier of HSV-1 or HSV-2, they may experience recurrent herpes outbreaks. Carriers of HSV-2 may notice herpes flare-ups more often than those with HSV-1. One study found that HSV-2 recurred in 80% of patients following an initial outbreak. Approximately 35% of patients may experience 6 or more outbreaks per year.  Men with genital herpes have a 20% higher rate of recurrences than women.

Valtrex typically relieves symptoms of repeated outbreaks rapidly. Similar to cases of first-time outbreaks, it is best to take valacyclovir as soon as symptoms occur. The recommended dosage for recurrent outbreaks is 500 mg twice a day over 3 days. It usually takes 48 hours for Valtrex to work.

If you’ve been diagnosed with shingles, you’ll likely be prescribed 1g of Valtrex 3 times a day for one week. Symptoms should begin to improve after 3 days.

For cold sores, doctors recommend 2 doses of 2g vlacyclovir taken 12 hours apart. But be patient; cold sores won’t disappear immediately.


How long starting Valtrex are you no longer contagious?

The herpes virus is very contagious and can easily spread via bodily fluids and skin contact. Once infected with herpes simplex virus type 1 or type 2, a person will be a carrier for life. There is no cure for herpes and no vaccinations exist right now.  

When you have cold sores or blisters on and surrounding your genital area, you will be most contagious, although it is important to understand that carriers of HSV-1 and HSV-2 can always transmit the infection.

When you have cold sores or blisters you should take additional precautions as follows:

  • Avoid kissing another person on the mouth or other areas of their body (although HSV-1 commonly causes cold sores, it can lead to genital herpes during oral sex)
  • Do not share cutlery, toothbrushes or towels
  • Use a condom when practicing vaginal or anal sex


Research has shown that Valtrex can reduce the risk of genital herpes transmission by up to 50% by decreasing viral shedding.

Taking Valtrex long-term is safe, and can decrease genital herpes outbreaks by up to 80%. However, you must tell your partner if you do have genital herpes, as they should be allowed to make up their own minds about the risks involved. 


It is important to emphasize that even after taking Valtrex, HSV continues to be contagious. Whilst antiviral drugs can decrease viral shedding and reduce the severity of HSV-1 and HSV-2, patients can still transmit the disease.



  1. Benedetti, J. (1994). Recurrence Rates in Genital Herpes after Symptomatic First-Episode Infection. Annals of Internal Medicine, 121(11), 847.
  2. Bonnar P. E. (2009). Suppressive valacyclovir therapy to reduce genital herpes transmission: good public health policy?. McGill journal of medicine : MJM : an international forum for the advancement of medical sciences by students, 12(1), 39–46.
  3. Thappa, D., & Nath, A. (2009). Newer trends in the management of genital herpes. Indian Journal of Dermatology, Venereology and Leprology, 75(6), 566.


Reviewed by Dr Roy Kedem, MD

Information last reviewed 07/12/21

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