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A cold sore is a painful blister that appears on the outside of the mouth close to or on the lips. Also known as fever blisters, cold sores develop due to herpes simplex virus type 1 (HSV-1) infections.

The HSV-1 virus is highly contagious and spreads through oral contact. While HSV-1 often leads to blisters around the mouth, it can also infect the genitals and lead to genital herpes.

Although there is no cure for HSV-1 infections, several treatment options can help reduce the healing time of cold sores and may even prevent them from appearing.

In this article, we discuss different types of medications that people can use to treat cold sores.

A person touches their face close to where they may have had a cold sore.Share on Pinterest
Image credit: Fabrice Poincelet/Getty Images

According to the American Academy of Dermatology (AAD), treating cold sores can shorten the duration of a flare-up and even prevent new cold sores from forming.

Various types of cold sore medication are available. Over-the-counter (OTC) treatments can help reduce pain, alleviate cracked or dry skin, and soften crusted or scabbed blisters.

Prescription cold sore medications include oral antiviral drugs. These treat the underlying HSV-1 infection. Antivirals may help reduce the frequency and severity of cold sore flare-ups.

Anyone who gets cold sores may benefit from cold sore medication. Healthcare providers often recommend higher doses of prescription antivirals for people with a weakened immune system.

The AAD recommend cold sore treatment for people who have:

  • multiple cold sores
  • frequent flare-ups
  • extremely painful sores
  • a cold sore that lasts longer than 2 weeks
  • sores that spread to other parts of the body, such as the hands or genitals

The AAD note that other people who could benefit from cold sore medications include those who have cold sores and one or more of the following conditions:

Doctors may also recommend cold sore medications for those receiving chemotherapy.

There is no cure for HSV infections or cold sores. However, the following prescription medications can treat cold sores and reduce the duration of flare-ups.

Zovirax (acyclovir)

Zovirax is the brand name of an antiviral drug called acyclovir, which inhibits the activity of HSV-1, HSV-2, and the varicella-zoster virus (VZV).

Acyclovir works by inserting itself into a virus’s DNA and preventing the virus from replicating.

It also contains inactive ingredients, such as:

  • magnesium stearate
  • microcrystalline cellulose
  • povidone
  • sodium starch glycolate

Zovirax comes in the form of 200-, 400-, or 800-milligram (mg) tablets. People can take Zovirax two to five times a day for 5–10 days, with or without food.

A doctor will tailor the exact dosage to suit a person’s symptoms and the type of infection. People with a weakened immune system may require higher dosages, while those with kidney problems may need lower dosages.

Valtrex (valacyclovir)

Valtrex is the brand name for the antiviral medication valacyclovir hydrochloride. The Food and Drug Administration (FDA) approved Valtrex for the treatment of cold sores in adults and children aged 12 years and older.

The recommended dosage for treating cold sores is two 2-gram (g) doses of Valtrex, which a person should take 12 hours apart.

People can take Valtrex orally as a tablet or a solution. The manufacturers recommend that people take Valtrex as soon as they start experiencing the symptoms of a cold sore, such as tingling, itching, or burning.

Healthcare providers do not recommend Valtrex for people who have a history of adverse reactions to Valtrex or Zovirax.

In people with advanced HIV, high doses of 8 g or more per day of this medication can lower platelet levels and damage small blood vessels.

Valtrex can also contribute to renal failure in older individuals with underlying kidney disease.

Famvir (famciclovir)

Famvir is the brand name of an antiviral called famciclovir, which transforms into penciclovir inside the body. This medication is effective against HSV-1, HSV-2, and VZV.

In a study of 701 adults with recurring cold sores, the participants who took a single 1,500-mg dose of Famvir had an average healing time of 4.4 days. This was about 2 days shorter than the healing time in the placebo group.

Famvir is available in 125-mg, 250-mg, and 500-mg oral tablets. The manufacturers recommend taking a single 1,500-mg dose of Famvir for recurring cold sores. People should start treatment as soon as they experience cold sore symptoms.

The recommended dosage for people with cold sores and HIV is 500 mg twice a day for 1 week.

Denavir (penciclovir)

Denavir is a topical cream that contains penciclovir. It is only approved for treating cold sores on the lips or face. A single gram of the cream contains about 10 mg of penciclovir.

Adults and children 12 years of age and older may apply this product to a cold sore every 2 hours for 4 days.

The prescription cold sore treatments above do carry some risk of side effects, which include those below.

However, these affect a very small percentage of people who use these medications.

Zovirax side effects

Zovirax side effects include:

Zovirax can also lead to the following nervous system side effects in older adults and people with kidney disease:

  • aggressive behavior
  • confusion
  • agitation
  • delirium
  • hallucinations
  • psychosis
  • seizure
  • coma

Valtrex side effects

Valtrex side effects include:

  • headaches
  • dizziness
  • nausea or vomiting
  • stomach pain
  • acute kidney failure
  • abnormal liver function tests
  • painful menstrual periods
  • depression
  • joint pain
  • skin rash

The following central nervous system side effects of Valtrex have occurred in older patients:

Famvir side effects

Famvir side effects include:

  • headache or migraine
  • nausea or vomiting
  • stomach pain
  • flatulence
  • diarrhea
  • fatigue
  • itchy skin
  • skin rash
  • painful menstrual periods

Denavir side effects

Denavir side effects include:

  • discolored patches of skin
  • skin irritation at the application site
  • increased or decreased sensation at the application site
  • changes in the sense of taste

While prescription medications can effectively reduce the frequency and severity of cold sores, OTC products can help alleviate cold sore symptoms.

People may wish to consider the following OTC treatments:

  • balms, such as Carmex, Blistex, and Lysine
  • lip balm that contains sunscreen
  • cold sore creams that contain docosanol, such as Abreva
  • cold sore patches, which are available to purchase in stores and online
  • OTC pain relievers, including ibuprofen and acetaminophen

An estimated 5–10% of people who have cold sores experience flare-ups more than five times a year.

Avoiding potential cold sore triggers can help reduce the frequency of cold sore flare-ups. Cold sore triggers include:

  • lip injuries
  • sun exposure and tanning beds
  • infections
  • fever
  • emotional stress
  • using steroids

Not all cold sores require treatment. Most cold sores heal on their own within 10 days.

People should contact a doctor if their cold sore does not improve or worsens after they treat it with OTC or at-home remedies.

People should also seek medical treatment if they have:

  • a cold sore that lasts longer than 2 weeks
  • numerous cold sores at once
  • a cold sore near their eye
  • a weakened immune system

Cold sores are blisters that appear on or near the lips. The herpes simplex virus type 1 (HSV-1) causes cold sores.

There is no cure for HSV-1 infections. However, several prescription and OTC treatment options can help decrease the duration, severity, and frequency of cold sore flare-ups.