Antiviral Drugs For Cold Sores

  • Saasha GovenderDiplomas in Journalism, Human Nutrition, and Effective Writing, Alison

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Antiviral drugs are created to target viral threats and play a key role in managing the spread and symptoms of viruses. They are considered the first line of treatment for cold sores, which are caused by the herpes simplex virus (HSV). Considering the vast antiviral market, how do we know which ones are good for cold sores? 

Let's find out below:

Understanding cold sores

Cold sores called fever blisters, are bumps, pimples, or ulcers that develop around the lips, mouth, and face. These sores are filled with fluid and can be inflamed, painful, and prone to breaking or bursting open.

The fluid inside the sores contains viral particles from the herpes simplex virus (HSV).  Being in contact with the fluid can cause new sores to form and spread on your body or cause the infection to spread to others you are in contact with. 

The virus is categorised into two main types: HSV-1 and HSV-2.1 

  • HSV-1 is identified by oral herpes (sores in and around the mouth)
  • HSV-2 is identified by genital herpes (sores in and around the genitals)

The World Health Organisation (WHO)2 states that an estimated 3.7 billion people under age 50 globally have HSV-1, which is the primary cause of cold sores or oral herpes. Once the HSV-1 is contracted, it stays in your skin indefinitely. 

The virus embeds itself in nerve cells near the spine, remaining inactive (dormant) without causing symptoms.3 So, you'll never know if you have the virus until a cold sore outbreak. Several factors can trigger these outbreaks.

These include: 

  • Stress
  • Fatigue
  • Dental work
  • Acute illness
  • Excess sun exposure
  • Exposure to extreme weather
  • Hormonal changes (such as with menstruation)

Commonly used antiviral drugs and how they work

Antiviral medications for cold sores are like strategic players against the herpes virus in your body. Their main job is to disrupt the virus's regular activity pattern by blocking specific processes that the virus needs to replicate and spread.4

It's important to know that these medications won't eliminate the virus because viruses are by nature quite resilient and cannot be eradicated. Instead, they aim to make outbreaks shorter, less frequent, and more severe while lowering the chances of passing the virus to others. 

Let's look at some of the most commonly used antiviral drugs on the market:

Brand name of drugZovirax FamvirValtrex
Active ingredientAcyclovirFamciclovirValacyclovir
Distinct featureAcyclovir is available in creams, ointments, IV solutions, and oral tablets. This wide-form variation offers versatility, allowing for external application and internal treatment.Famciclovir has a longer duration of action, which means you don't have to take several doses daily.Valacyclovir is converted into acyclovir in the body but with the added advantage of better oral bioavailability. This allows for lower doses and less frequent dosing compared to traditional acyclovir.
Studies A study5 reported that acyclovir effectively reduced the duration of cold sore pain. This effect was apparent whether the treatment was taken at an early or late stage. Adverse events were mild and infrequent. Scientific evidence6  found that a single dose of famciclovir daily is as effective at healing cold sores as multiple doses. The single dose was also better at reducing pain and tenderness than the multiple doses and proved to be a convenient treatment for recurring cold sores, improving the overall management of the condition.A clinical trial7 showed that valacyclovir therapy, taken at the first symptom of a cold sore, produces positive results. It reduces the duration of an outbreak episode, lesion healing times, and the duration of pain and/or discomfort felt. Valacyclovir is named as a safe and effective treatment of cold sores with simple and convenient dosing.

These antiviral drugs are essential in managing cold sore outbreaks, but it's crucial to use them under the direction of a healthcare professional to ensure proper dosage and frequency schedules for maximum effectiveness.

Combating cold sores with antiviral drugs

As we mentioned earlier, antiviral drugs are designed to disrupt the growth and multiplication of viruses. They can block any steps a virus uses to copy itself. They can sometimes be mistaken for antibiotics, but their functions have distinct differences - antibiotics target bacteria, while antivirals chase after viruses.8

This means that antibiotics cannot be used to treat or manage cold sore breakouts. You have to be quick to the trigger when using antiviral drugs for cold sores. In other words, use these drugs at first sight or when symptoms of cold sores appear.9 Treatment must ideally start within 24 hours of the first symptoms arising.

This goes for both oral and topical antiviral drugs. Early intervention with antiviral drugs helps  speed up healing processes and reduce symptom severity and how long a cold sore lasts. If the treatment is started later, it might no longer help because the virus would have spread along the nerve fibres.10

Side effects, interactions, and contraindications of antiviral drugs

Side effects, interactions, and contraindications are the most important to consider before starting treatment, as they can determine treatment outcomes. Antiviral treatments are typically considered well-tolerated.

But as with any drug, there is a possibility of side effects rearing their ugly heads. The most common side effects noted include nausea and headaches. These side effects are often mild and manageable and disappear soon after the body becomes familiar with the effects of the treatment.

It's still essential to monitor the severity of these side effects and be on the lookout for strange or uncomfortable effects, as this may signal an issue and require medical attention. Now that side effects are out, let's look at possible interactions and contraindications.

Interactions refer to other incompatible treatments that may cause adverse effects when used with antiviral drugs. On the other hand, contraindications point to conditions that may not agree with antivirals.

Possible interactions and contraindications include:


  • Other Antiviral Medications: Combining different antiviral drugs may lead to the occurrence of side effects or reduced effectiveness.
  • Probenecid (for Acyclovir): Probenecid may increase the concentration of acyclovir in the body, potentially causing higher levels of the drug in the body. This may result in an increased risk of side effects.
  • Medications Metabolized by the Kidneys (for Valacyclovir): Since Valacyclovir is primarily excreted through the kidneys, drugs that affect kidney function may interact with it.11


  • Allergy or Hypersensitivity: Individuals with known allergies or hypersensitivity to the specific antiviral drug or ingredients in them.
  • Renal Impairment: Those with kidney issues may be unable to use certain antiviral drugs or need a dose adjustment.  
  • Pregnancy and Breastfeeding: The safety of these drugs during pregnancy or breastfeeding may vary. Consulting with a healthcare professional before use is necessary in this case.
  • Immunocompromised Individuals: Antiviral drugs may require special consideration in those with compromised immune systems, like those with HIV/AIDS.
  • Certain Medical Conditions: Specific medical conditions, such as hepatic impairment or neurologic disorders, may require careful monitoring or dosage adjustments.

Enhancing the efficacy of antiviral drugs

Antiviral drugs are effective on their own, but there is no harm in lending their efficacy a helping hand to get rid of cold sores quicker. One of the ways to do this is through lysine. Lysine is an essential amino acid that the body uses to heal and grow.12

The acid can interrupt the production of arginine – another amino acid that helps HSV-1 spread and grow. The body does not make lysine, but it can be sourced from foods like eggs, fish, meat, or poultry, among other foods or supplements.13

You can also make a lysine paste, which can be applied directly to cold sores. This is an ideal pairing when using an oral antiviral treatment. Apply lysine paste to the affected area every 2 hours for 11 days to clear up cold sores.

Follow the steps below after consulting with your GP:

  • Combine 1g of lysine powder with 2 tablespoons of water or until you get a thick paste 
  • Apply the paste on the cold sores using a Q-Tip or cotton pad nightly
  • The leftover paste can be kept in the fridge

You can also incorporate zinc and vitamin C supplements into your lifestyle, as they can help boost your immune system. Adding vitamin C to Lysine use can produce favourable outcomes as vitamin C transforms Lysine into collagen. A study shows that collagen can regulate wound healing. This shortens the duration of cold sore breakouts while promoting better healing.14


Antiviral drugs for cold sores have revolutionized the management of HSV infections that result in cold sores. It provides individuals with a practical option to alleviate symptoms and the duration and spread of outbreaks. The multi-form availability of some antiviral drugs offers versatility and supports various treatment approaches, allowing healthcare professionals to tailor the medication to the specific needs and conditions of individual patients. Early intervention at the onset of symptoms is crucial for optimal results. However, there are antiviral options that support both early and late intervention, which is convenient for those who aren’t quick. Antiviral drugs are also science-certified, safe, and effective and can be used as a management option or preventative measure, providing reassurance to both healthcare providers and patients about their reliability in controlling viral infections and reducing the risk of complications.


  1. Herpes: HSV-1 and HSV-2 [Internet]. [cited 2023 Dec 15]. Available from:
  2. Herpes simplex virus [Internet]. [cited 2023 Dec 15]. Available from:
  3. Cold sore [Internet]. NHS inform. [cited 2023 Dec 15]. Available from:
  4. Kausar S, Said Khan F, Ishaq Mujeeb Ur Rehman M, Akram M, Riaz M, Rasool G, et al. A review: Mechanism of action of antiviral drugs. Int J Immunopathol Pharmacol [Internet]. 2021 Mar 16 [cited 2023 Dec 15];35:20587384211002621. Available from:
  5. Spruance SL, Nett R, Marbury T, Wolff R, Johnson J, Spaulding T. Acyclovir cream for treatment of herpes simplex labialis: results of two randomized, double-blind, vehicle-controlled, multicenter clinical trials. Antimicrob Agents Chemother [Internet]. 2002 Jul [cited 2023 Dec 15];46(7):2238–43. Available from:
  6. Hull C, Spruance S, Tyring S, Hamed K. Single-dose famciclovir for the treatment of herpes labialis. Curr Med Res Opin. 2006 Sep;22(9):1699–702. 
  7. Spruance SL, Jones TM, Blatter MM, Vargas-Cortes M, Barber J, Hill J, et al. High-dose, short-duration, early valacyclovir therapy for episodic treatment of cold sores: results of two randomized, placebo-controlled, multicenter studies. Antimicrob Agents Chemother [Internet]. 2003 Mar [cited 2023 Dec 15];47(3):1072–80. Available from:
  8. Dance A, Magazine K. Why are there so many antibiotics but so few antiviral drugs? – the wire science [Internet]. 2021 [cited 2023 Dec 15]. Available from:
  9. [Internet]. 2018 [cited 2023 Dec 15]. Cold sores. Available from:
  10. Bello-Morales R, Andreu S, López-Guerrero JA. The role of herpes simplex virus type 1 infection in demyelination of the central nervous system. Int J Mol Sci [Internet]. 2020 Jul 16 [cited 2023 Dec 15];21(14):5026. Available from:
  11. Taburet AM, Singlas E. Drug interactions with antiviral drugs. Clin Pharmacokinet. 1996 May;30(5):385–401. 
  12. Spallotta F, Cencioni C, Straino S, Sbardella G, Castellano S, Capogrossi MC, et al. Enhancement of lysine acetylation accelerates wound repair. Commun Integr Biol [Internet]. 2013 Sep 1 [cited 2023 Dec 15];6(5):e25466. Available from:
  13. Larson A, Goodman S. Table 5. [nutritional requirements for l-lysine, l-carnitine,... ]. [Internet]. 2019 [cited 2023 Dec 15]. Available from:
  14. Mathew-Steiner SS, Roy S, Sen CK. Collagen in wound healing. Bioengineering (Basel) [Internet]. 2021 May 11 [cited 2023 Dec 15];8(5):63. Available from:

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This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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Saasha Govender

Diplomas in Journalism, Human Nutrition, and Effective Writing

I am a seasoned health writer with extensive experience in the medical field spanning over several years. My expertise is a fusion of investigative prowess and an unwavering passion for all facets of healthcare. Holding diplomas in Journalism, Human Nutrition, and Effective Writing, along with certification and practical experience in Ancillary Healthcare and Telehealt —I possess a solid foundation that enables me to navigate the scientific intricacies of medical/health-related topics.

My approach goes beyond the surface, as I aim to translate complex theories into reader friendly information without sacrificing medical stance. This ensures readers gain accurate knowledge that can drive change toward improving their health.

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