Cold sores are caused by certain variants of the herpes simplex virus (HSV). HSV is classified into two categories: HSV Type 1 (HSV-1) and HSV Type 2 (HSV-2).
HSV-1 (oral herpes) is typically transmitted via oral-to-oral contacts, such as kissing and is primarily responsible for the infection in or around the mouth (cold sores).
HSV-2 is a sexually transmitted infection that is commonly known as genital herpes. Infection with HSV is quite common, with estimates showing that 50% to 80%¹ of the American adult population have HSV-1. According to the CDC, 11.9% of people aged 15–49² in the United States have an HSV-2 infection.
While cold sores are mainly attributed to HSV-1, either strain of the HSV virus can spread to the mouth or genitals through close contact. Once in the body, the virus can remain dormant for long periods in between outbreaks. People with HSV-1 typically experience about one episode yearly, while HSV-2 flare-ups are more common.
Your doctor may prescribe Valtrex to control cold sores and other herpes outbreak symptoms when these outbreaks occur.
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Valtrex (generic name valacyclovir) is a prescription antiviral drug used to treat diseases caused by certain types of viruses, such as HSV. It’s one of the most widely used and effective drugs for treating and managing cold sores.
Valtrex can shorten the duration of cold sores, but it does not cure oral herpes. More importantly, Valtrex will not prevent you from spreading the infection to other people.
Valtrex is also used to treat genital herpes (genital lesions) and shingles (herpes zoster) in adults. Doctors may prescribe Valtrex for chickenpox in children at least two years old.
Antiviral drugs don’t kill viruses; they inhibit their ability to grow and multiply. Valtrex slows the growth and spread of HSV to help the immune system fight the infection. That way, the drug may help shorten spells of cold sores and blisters during oral herpes outbreaks.
In other words, Valtrex and similar antiviral medications treat cold sores by limiting how much the HSV-1 virus grows and spreads. Preventing the virus from growing and spreading reduces the intensity of cold sores and other symptoms associated with HSV-1 infection or outbreak.
Cold sore medication can be administered orally or in antiviral creams. Creams must be applied several times daily and are less effective than oral medications. Oral tablets are available in 500-milligram and 1-gram strengths
For an adult looking to treat cold sores, a healthcare professional will typically prescribe two grams twice daily, taken 12 hours apart, for ten days. For the best outcomes, oral medications such as Valtrex should be taken at the initial sign of a cold sore.
Note that Valtrex is not just used to treat cold sores. A doctor may also prescribe Valtrex or another antiviral medication to prevent cold sores. Taking Valtrex daily reduces the chances of cold sores recurring by about 30%.
The time it takes your symptoms to go away after Valtrex is administered will depend on a few factors. These include your metabolism, the severity of your symptoms, and age. Usually, cold sores can go away on their own in seven to 10 days.
According to a Harvard Health³ publication, antiviral medications such as Valtrex can slightly shorten the time it takes for cold sores to heal completely by a day or two.
In another study,⁴ participants who took Valtrex within two hours of noticing their first cold sore symptoms had shorter cold sore flare-ups by about one day compared to those who didn’t take the drug.
Ultimately, the speed of recovery depends on how soon you recognize the symptoms and get started on the medication. Therefore, you must start treatment as soon as you notice cold sore symptoms developing. Follow your doctor’s instructions and ensure you complete the entire course of the medication, even if your cold sores heal before the end of the period.
Taking Valtrex after a cold sore appears provides fast and effective relief from the blisters and other symptoms of HSV-1 infection. You should take the medication as soon as you notice cold sores developing.
Being familiar with the other symptoms of oral herpes can help you sense a looming outbreak and start seeking relief options.
So, what are the symptoms of an oral herpes outbreak? Well, in most cases, recurring HSV-1 infections are asymptomatic, but if present, symptoms can include:
Redness, tingling, burning, itchiness, and swelling in the lips or the area where the cold sores will erupt
Painful, fluid-filled blisters start to erupt on the edges of the lip or inside the mouth
Blisters turn to sores as the fluid begins to leak
The sores begin to crust over and heal after a few days
These are the most common signs and symptoms of a recurring HSV-1 infection. Start medication or seek other relief options when you notice the initial redness, itching, pain or heat, and swelling in the lips or other areas around your mouth.
Note that the initial HSV-1 infection is usually the worst. You may experience severe, flu-like symptoms, including headache and swollen lymph nodes. The signs of an initial or recurring HSV-1 infection may be similar to other conditions, so always consult a doctor for an accurate diagnosis.
Cold sores can be quickly passed from person to person by direct skin contact with the affected area. The infection can spread from when you first feel tingling or burning until after it has scabbed over, which usually takes about 15 days. However, cold sores are most infectious when there are oozing blisters.
Do cold sores stop being contagious after taking Valtrex? No, cold sores don’t stop being contagious until after they are completely healed. Valtrex prevents the virus from growing and spreading, speeds up the healing process, and significantly reduces the period you remain contagious.
Valtrex is available through prescription only and may have specific side effects in some people. According to the National Library of Medicine,⁵ the most common side effects in people using Valtrex for cold sores are:
Valtrex can also trigger allergic reactions in some people. Call your doctor immediately if you exhibit signs of an allergic reaction to Valtrex. These include swelling of your tongue, throat, lips, or face; difficulty breathing; or hives.
Although it’s rare, Valtrex can also cause life-threatening side effects. Stop taking Valtrex and get emergency medical help if you experience hallucinations, confusion, speech problems, seizure, kidney failure, or other serious side effects.
It’s generally safe to take Valtrex simultaneously with other medications. There are no known significant drug interactions between Valtrex and other medications. However, inform your physician about all other medicines you use.
Better still, bring a complete list of all the prescription drugs and supplements you’re taking to your doctor. Your doctor may need to adjust your dosage or perform specific tests when taking other medicines with Valtrex.
If you are experiencing a herpes flare-up, start taking Valtrex as soon as you notice the initial symptoms—redness, tingling, burning, itchiness, and swelling in and around the mouth. That’s when the drug is most effective.
Take Valtrex as prescribed by your healthcare provider. Do not take the drug in higher or lower dosages or for more extended periods than your doctor recommends. Stick to the prescription even if your symptoms improve before the prescribed length ends. You risk making the virus resistant to antiviral medications by skipping doses.
Additionally, you should take Valtrex with a full glass of water (eight ounces). The water will help your kidneys process the drug more efficiently. Swallowing medications such as Valtrex without enough water may prevent them from acting properly. In some cases, it may even lead to adverse side effects.
Life happens, and you may find that you’ve missed your Valtrex dose through no fault of your own. If you happen to miss a dose for any reason, don’t panic. Take the missed dose as soon as you are able.
You can miss the skipped dose and resume your regular schedule if it’s almost time for your next scheduled dose. This is the only time you should skip a dose. You should never take an extra Valtrex dose to make up for the one you didn’t take.
Even though Valtrex is generally safe and relatively effective at treating cold sores and other HSV symptoms, it shouldn’t be taken by everyone. You should discuss with your healthcare provider before taking Valtrex if you:
People 65 years or older are more likely to experience adverse side effects after taking Valtrex. However, this doesn’t mean that older adults can’t take this medication if they are experiencing a herpes flare-up. Your healthcare provider can prescribe a lower dose.
Some underlying health conditions can make it unsafe for some people to take Valtrex. For instance, people with kidney problems or kidney disease could experience adverse symptoms from taking Valtrex. You should also talk to your doctor before taking Valtrex if you have HIV.
Valtrex is not recommended for treating cold sores in children 11 years and younger. However, it can treat other viral infections, such as chickenpox, in children two years and older.
You may wonder if you can take Valtrex while pregnant or when breastfeeding. As an expectant mother, talk to your healthcare provider if you’re thinking about taking Valtrex. They will tell you how it might affect your pregnancy. Your doctor may prescribe Valtrex if the benefit is felt to outweigh the risk of potential side effects.
Generally, Valtrex is safe to take during breastfeeding. Again, you should always consult a healthcare professional about taking it while nursing.
HSV-1 infections can be asymptomatic or have mild symptoms that are unnoticeable. When symptoms occur, oral herpes is characterized by open sores or painful blisters in and around the mouth (cold sores). HSV-1 can remain dormant for long periods in between periodic flare-ups.
Valtrex is an antiviral medication that treats cold sores and other HSV symptoms. The drug is most effective when you take it as soon as you notice cold sores developing. When taken correctly, the drug can provide relief and reduce the risk of you spreading the infection to other people.
Valtrex does not heal the cold sores or the underlying HSV infection. Instead, it may reduce the duration of blisters and cold sore flare-ups. Valtrex is not an over-the-counter medication, so you’ll need a prescription to treat your cold sores or oral herpes flare-up.
Although Valtrex is generally safe and effective at treating cold sores, it shouldn’t be taken by just anyone. If you notice cold sores or any other symptoms of an HSV-1 outbreak, talk to your doctor about treatment and relief options as soon as possible.
Herpes: HSV-1 and HSV-2 | Johns Hopkins Medicine
Genital herpes – CDC detailed fact sheet | Centers for Disease Control and Prevention
Preventing cold sores | Harvard Health Publishing
Herpes simplex virus | World Health Organization