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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.

This article discusses different types of medication that people can use to treat cold sores.

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 medications are available. Over-the-counter (OTC) treatments can help reduce pain, alleviate cracked or dry skin, and soften crusted or scabbed blisters.

Learn more about cold sore creams.

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 professionals often recommend that people with immune conditions and severe HSV take medication several times per day.

The AAD recommends cold sore treatment for people who have:

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

The AAD notes 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.

HSV infections or cold sores have no cure. 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 inserts itself into a virus’s DNA and prevents it from replicating.

It also contains inactive ingredients, such as:

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

Zovirax comes in 200-, 400-, or 800-milligram (mg) tablets. People can take Zovirax two to five times per 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. The Food and Drug Administration (FDA) approved Valtrex to treat cold sores in adults and children ages 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 manufacturer recommends people take Valtrex as soon as they start experiencing the symptoms of a cold sore, such as tingling, itching, or burning.

People living with HIV or other immune-compromising conditions will need a 500-mg dose twice per day.

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

Valtrex can cause complications in some people. For example, it can 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 manufacturer recommends 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 living with cold sores and HIV is 500 mg twice per day for 1 week.

Denavir (penciclovir)

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

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

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

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

Zovirax side effects

Zovirax side effects include:

High doses of acyclovir and valacyclovir can have adverse neurological side effects, including:

  • muscle jerks
  • tremors
  • slow or slurred speech
  • delirium
  • hallucinations
  • 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

Evidence that supports the use of natural or home remedies for the treatment of cold sores is limited. Most home remedies include options that others have tried and found worked for them. Some popular options with some supportive, often older evidence include:

  • Rhubarb and sage: There is some evidence that rhubarb and sage cream is of similar efficacy to Zovirax, which contains acyclovir. The participants who used sage, rhubarb-sage, and Zovirax had an average healing time of 7.1, 6.7, and 6.5 days respectively. Additionally, participants who used the rhubarb-sage cream reported less pain than those who used the sage-only cream.
  • Kanuka honey: A 2018 study found no statistical difference between the time it took for cold sores to heal when using medical grade kanuka honey or 5% acyclovir cream. The authors state that it took 8–9 days for participants’ skin to heal with both kanuka honey and acyclovir cream.
  • Lemon balm: Lip balms that use lemon essential oil may help reduce the appearance of cold sores. An older 2012 study found that lemon extract has an antiviral mechanism that can affect how the herpes virus attaches to cells.
  • L-lysine supplements: A 2017 literature review states that, while there is not sufficient clinical evidence that l-lysine supplements are effective against the herpes virus, participants in studies reported a subjective improvement in their experience of having the virus.
  • Licorice root: Licorice root contains glycyrrhizic acid, which research suggests may have antiviral properties. There is evidence that licorice root can interrupt the gene expression of the herpes virus and can limit the virus’s ability to attach to cells.
  • Peppermint oil: Research suggests that peppermint extract has a strong antiherpetic effect. Additionally, peppermint oil may be effective against acyclovir-resistant herpes strains. Peppermint extract can decrease resistant herpes strain infectivity by up to 85%.

A person should discuss using a natural or home remedy with a doctor or another healthcare professional.

Learn more about treating herpes at home.

An estimated 5–10% of people with 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 within 2 weeks.

People should contact a doctor if their cold sore does not improve or worsens after treating 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 and some home therapies can help decrease the duration, severity, and frequency of cold sore flare-ups.