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Can L-Lysine Prevent Painful Cold Sores?

Readers report that the supplement L-lysine can help prevent recurrent fever blisters caused by HSV-1.
Can L-Lysine Prevent Painful Cold Sores?
Closeup of a  common cold sore virus herpes.

Cold sores are painful lesions on or near the lips. Sometimes people call them fever blisters because they have a fluid-filled appearance and because an infection with a fever may bring them on. The common virus herpes simplex 1 (HSV-1) causes cold sores. Scientists don’t seem to know why this virus can hide out for months or years without causing a visible problem and then an event triggers the formation of an unsightly, uncomfortable blister. People who have recurrent cold sores can prevent them with antiviral medications like acyclovir (Zovirax) or famciclovir (Famvir). Does taking the supplement L-lysine prevent their appearance as well?

How Can You Treat a Cold Sore?

Q. For years, I was susceptible to cold sores from eating too much sugary food, from stress and from sun exposure.

In my early 30s, I was picking up a prescription for acyclovir ointment my dentist prescribed for a cold sore. The pharmacist told me to take daily doses of the amino acid L-lysine. Once I started taking it, my cold sores stopped almost completely. I hardly get them anymore, although I know I still have the virus in my system.

L-Lysine to Prevent Cold Sores:

A. We have heard from many other readers that L-lysine supplements can help prevent the development of cold sores. There is, unfortunately, little research on the use of this amino acid as a cold sore remedy. However, a review concluded that in combination with a low-arginine diet, high doses of L-lysine can prevent lesion recurrences (Integrative Medicine, June 2017). 

We would like to see large, well-controlled, long-term trials to assess the success of this approach. However, there is little, if any, financial incentive for a drug company to conduct such research.

Another Reader Praises L-Lysine:

You are not the only person to find L-lysine helpful in controlling fever blisters. Years ago, we heard from this reader.

Q. More than 20 years ago I came across an article promoting L-lysine as a preventive measure against cold sore outbreaks. Having suffered with this virus since adolescence, I was motivated to try the supplement.

In my experience, L-lysine is a miracle drug. I used to have at least one outbreak a month, but I now only feel the initial “tingle” of a cold sore if I have overindulged in caffeine, been under an abnormal amount of stress or spent too much time in the sun. I take 1000 mg a day, every day. If I feel an outbreak coming, I triple the dose for a couple of days and the outbreak is prevented.

A. Many people report, like you, that L-lysine seems helpful in preventing or healing cold sores. Double-blind studies on L-lysine for cold sores have produced mixed results. Moreover, there has been surprisingly little research in recent years. This amino acid appears relatively safe, although some people report digestive upset at high doses.

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About the Author
Terry Graedon, PhD, is a medical anthropologist and co-host of The People’s Pharmacy radio show, co-author of The People’s Pharmacy syndicated newspaper columns and numerous books, and co-founder of The People’s Pharmacy website. Terry taught in the Duke University School of Nursing and was an adjunct assistant professor in the Department of Anthropology. She is a Fellow of the Society of Applied Anthropology. Terry is one of the country's leading authorities on the science behind folk remedies. .
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  • Mailoo VJ & Rampes S, "Lysine for herpes simplex prophylaxis: A review of the evidence." Integrative Medicine, June 2017.
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