Cold Sores (Herpes Simplex Type 1) and Lysine

L-lysine (lysine) is an amino acid that is a popular treatment for herpes infections. Supplementing regularly with lysine might reduce the number and intensity of cold sore outbreaks.⁹ Lysine is probably not effective at treating outbreaks if you wait and take it at the onset of an outbreak¹⁰; lemon balm (melissa) works better for that purpose.

Test tube research suggests that lysine fights the herpes simplex virus by blocking arginine, an amino acid the virus needs in order to replicate.⁷

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Taken regularly in sufficient doses, lysine supplements appear to reduce the number and intensity of herpes flare-ups.⁹

One double-blind, placebo-controlled study followed 52 participants with a history of herpes flare-ups.¹¹ While receiving 3 g of L-lysine every day for 6 months, the treatment group experienced an average of 2.4 fewer herpes flare-ups than the placebo group—a significant difference. The lysine group's flare-ups were also significantly less severe and healed faster.

Another double-blind, placebo-controlled crossover study on 41 subjects also found improvements in the frequency of attacks.¹² Interestingly, this study found that 1,250 mg of lysine daily worked, but 624 mg did not.

Other studies, including one that followed 65 individuals, found no benefit, but they used lower dosages of lysine.^13,14

Lysine is widely available in supplement form. The richest food sources of lysine are animal proteins such as meat and poultry, and it is also found in dairy products, eggs, and beans.

In order for lysine to be helpful in decreasing the number and intensity of cold sore outbreaks, it probably needs to be taken regularly and at a high enough dose. For instance, one study found that 1,250 mg of lysine daily worked, but 624 mg did not.¹²

Test tube research suggests that lysine fights the herpes simplex virus by blocking arginine, an amino acid the virus needs in order to replicate.⁷ For this reason, lysine might be most effective when used in conjunction with a low-arginine diet. (Arginine is found in dairy products, meat, poultry, fish, nuts, and chocolate.) However, this widely stated claim has not been proven. (Note that if this is true, it would be essential to avoid taking arginine supplements if you have herpes.)

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Safety Issues

Although lysine is an essential part of the diet, the safety of concentrated lysine supplements has not been well studied. In animal studies, high dosages have caused gallstones and elevated cholesterol levels, ¹ so you may want to use caution when using lysine if you have either of these problems. Maximum safe dosages for young children, pregnant or nursing women, or those with severe liver or kidney disease have not been established.

Interactions You Should Know About

If you are taking lysine to treat herpes, arginine might counteract the potential benefit. ²

1. Kritchevsky D, Weber MM, Klurfeld DM. Gallstone formation in hamsters: Influence of specific amino acids. Nutr Rep Int. 1984;29:117-121.
2. Griffith RS, DeLong DC, Nelson JD. Relation of arginine-lysine antagonism to herpes simplex growth in tissue culture. Chemotherapy. 27(3):209-13.

7. Griffith RS, DeLong DC, Nelson JD. Relation of arginine-lysine antagonism to herpes simplex growth in tissue culture. Chemotherapy. 27(3):209-13.
9. Flodin NW. The metabolic roles, pharmacology, and toxicology of lysine. J Am Coll Nutr. 1997;16:7-21.
10. Milman N, Scheibel J, Jessen O. Failure of lysine treatment in recurrent herpes simplex labialis [letter]. Lancet. 1978;2:942.
11. Griffith RS, Walsh DE, Myrmel KH, et al. Success of L -lysine therapy in frequently recurrent herpes simplex infection: treatment and prophylaxis. Dermatologica. 1987;175:183-190.
12. McCune MA, Perry HO, Muller SA, et al. Treatment of recurrent herpes simplex infections with L-lysine monohydrochloride. Cutis. 1984;34:366-373.
13. DiGiovanna JJ, Blank H. Failure of lysine in frequently recurrent herpes simplex infection. Treatment and prophylaxis. Arch Dermatol. 1984;120:48-51.
14. Milman N, Scheibel J, Jessen O. Lysine prophylaxis in recurrent herpes simplex labialis: a double-blind, controlled crossover study. Acta Derm Venereol. 1980;60:85-87.