Does it work? Can lysine help prevent cold sores?


BACKGROUND:Lysine is an essential amino acid which means it cannot be made within the body and must be regularly consumed in the diet. About 20 different amino acids are used to make all our proteins. Lysine is readily available in red and white meats, eggs, cheese and most beans and peas.

Supplemental use of lysine has been suggested as a way to prevent the recurrence of cold sores. These are infections caused by herpes simplex virus type 1 (HSV1). Several different strains of herpes viruses cause different types of infection. Genital herpes is usually caused by HSV2 and infection by one type is not necessarily related to other infections.

After someone gets the first cold sore, the virus travels to nearby nerve cells where it resides for the rest of the person’s life. Mostly the virus is dormant, but reactivates from time to time, leading to another cold sore. Antiviral medications are available as tablets and creams to shorten the duration of an outbreak, but the infection is never truly cured.

The role of lysine supplementation in cold sores was suggested when it was found that growth of HSV1 is highly dependant on another amino acid called arginine. This is found in large amounts in nuts, chocolate, wheat, oats and gelatine.

Early studies with the viruses suggested that lysine and arginine compete with one another within the virus. This led to the hypothesis that increasing lysine and decreasing arginine could help to slow the growth of HSV1 and reduce the frequency and duration of cold sores.


The first studies in this area were conducted in the 1970s. These included small numbers of people, often didn’t report statistical analyses and were not double-blinded. However, a general pattern appeared that the severity and duration of cold sores were not reduced by lysine, but sometimes the time between recurrences was lengthened. Also, doses of more than 1g per day seemed to be required for an effect.

Better designed studies were conducted in the 1980s where different doses of lysine were tested. However, the studies still had limitations such as enrolling people with different types of herpes infections. They continued to involve small numbers of people, making it difficult to statistically validate the significance of the results.

Some of the studies asked people to compare the number of cold sores they had when taking lysine with past experiences when they were not taking it. Relying on people’s memory can be unreliable. Overall, however, the pattern continued that lysine appears to reduce the frequency of cold sores, but not their duration or severity.


The average, non-vegetarian diet in developed countries contains 6-10g lysine, with 1-1.5g required for daily metabolism. The body is thus able to tolerate large quantities of lysine. Adverse effects from large supplemental doses are usually limited to intestinal problems. However, lysine contains nitrogen which must be eliminated by the liver or kidneys. The additional nitrogen consumed when taking lysine supplements could be problematic for those with kidney or liver problems. Anyone with those problems should discuss lysine supplements with a doctor before taking them.


Current evidence suggests that lysine supplements may help reduce the frequency of cold sores, though this is not likely to relieve the symptoms when they occur. The studies available have limitations and larger, well-designed studies are needed to provide a clearer answer to lysine’s effectiveness. Large doses are required, with at least 1g per day usually recommended, which may cause intestinal problems. Other dietary factors should be considered to identify foods that may trigger or relieve cold sores.

Dónal O’Mathúna has a PhD in pharmacy, researching herbal remedies, and an MA in bioethics, and is a senior lecturer in the School of Nursing, Dublin City University