Q. You recently mentioned the value of l-lysine for dealing with cold sores. I have struggled with cold sores and fever blisters for over 50 years.

About 20 years ago, I first tried l-lysine. I’ve found that taking 1000 mg twice a day at the first sign of a “tingle” stops the cold sore immediately.

If I miss that signal and a blister forms, taking l-lysine makes the blister disappear within a few days: no scabs, no inflammation. My brother has had similar good results with l-lysine.

A. Like you, many people who suffer from recurrent cold sores report that the amino acid l-lysine can be useful in shortening the attack. Despite such testimonials, however, there is a surprising lack of recent clinical trials supporting the use of l-lysine.

Older studies were inconclusive. Without better research it is hard to say whether this natural product is really better than placebo. On the other hand, l-lysine appears safe.

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  1. tammie

    I am allergic to fever blisters cold sores. When I was 19 they caused herpetic ulcers in my eye. After five surgeries including a cornea transplant I still can’t see out of my eye and I’m 59. Ulcers from the fever blisters got into the new cornea.

    I have been through a lot because of cold sores I’ve taken all kinds of prescription meds the one that does help over the counter is lysing like the other lady said I can feel a tingle coming on start taking the pills and I never get blisters. So I guess that’s proof and it’s a lot cheaper than zovirax or Acyclovir.

  2. ET

    I have suffered with cold sores for over 30 years. They would get really big and take weeks to go away, sometimes leaving a red spot that took even longer to disappear. I took Lysine orally and it helped with future outbreaks but the best thing I did was to break the tablet add a little water to make a paste and apply to the cold sore or the tingling area and leave it on overnight. The cold sore, if erupted, is gone by the morning and if it is just starting, never erupts. I don’t care about “studies” because when something works, it works!

  3. CW

    Lysine has definitely helped me to control cold sores, which I’ve suffered with for nearly 40 years. Other factors seem to be important as well during an outbreak: sufficient sleep to bolster immune system (seriously, it does make a difference); staying out of the sun for excess periods of time; and finally, avoiding chocolate and most kinds of nuts. L’arginine can be found in these foods in generous doses and it seems to promote the growth of cold sores, while lysine seems to suppress growth. I’ve experienced cold sores for too many years to be reacting to a “placebo effect”. Chocolate and nuts make my cold sores worse. Sleep and lysine (500 mg twice a day, at a minimum) are helpful in minimizing the duration of my outbreaks.

  4. Casey Marie

    I read somewhere that if you take 1500mg of lysine daily, you should take a two week break from it every 6 months. Does anyone know anything about this?

  5. CE

    When my son was in elementary school he regularly developed large cold sores on his face when he was overtired. No medicine the doctor gave him ever helped. I believe what he had was herpes related. My husband always took bicarbonate of soda for cold sores so we tried this on my son. The sores went away almost overnight as soon as he drank some bicarb. We also tried Camphophenique, which helped but the bicarb did the trick. The doc said this was “impossible”!!

  6. Scott

    For years I suffered fever blisters once or twice a year. Someone recommended taking alka selzer at the first sign of a fever blister. Works like a charm. I’ve had only one or two slight blisters in almost 5 years.

  7. mike

    I used to get cold sores regularly, several times a year. My daughter-in-law, a nutritionist, suggested lysine and I take 500 or 600 mg tablets daily. No outbreaks in years. No noticeable side effects.

  8. BH Shaw

    I’ve also had similar results with tee tree oil, applied at first tingle. If later, it still keeps the eruption small and pain-free.

  9. mary

    I find that using 500 mg of l-lysine daily keeps the fever blisters away. If I miss just a couple days, I will get one. Then I double up again and it goes away quickly. Thanks

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