Lysine: Food Sources, Cold Sores and Supplements
Lysine is an essential amino acid found in protein foods. What reviews say about cold sores, a Ghana trial, a tolerated-intake estimate, and who should ask a clinician first.
Content last updated . This page has not been medically reviewed.
What is Lysine good for?
What the body uses it for, and how strong the evidence is. A normal job in the body is not proof that extra supplements add benefit; each card says which.
Protein building block
Established roleLysine is one of the amino acids the body strings together to make proteins.
Supplements: Normal role of lysine from food; no good evidence that extra supplemental lysine adds benefit when intake is adequate.
Growth and tissue repair
Established roleThe body uses amino acids such as lysine to build proteins for growth and to repair tissue.
Supplements: Normal role of lysine from food; no good evidence that extra supplemental lysine adds benefit when intake is adequate.
Starting material for carnitine
Established roleTogether with methionine, lysine is used by the body to make carnitine.
Supplements: Making carnitine is a normal role; supplements are not shown to improve energy in people with adequate intake.
Immune and gut illness in a low-intake setting
Preliminary or mixedIn a Ghana trial in poor households where lysine intake was at risk, lysine supplements reduced diarrhoeal illness in children and respiratory illness in men.
Supplements: One trial in a low-intake population; not shown to help people who eat enough varied protein.
Cold sores (herpes simplex labialis)
Not enough evidenceLysine is often used for cold sores, but the 2015 Cochrane review of 32 trials found no evidence of benefit for lysine in preventing them.
Supplements: Evidence is insufficient or mixed; the more rigorous review did not find efficacy. Ask a pharmacist about proven options.
Essential amino acid that must come from food
Established roleThe body cannot make lysine, so it has to come from the diet, from animal foods, soy, beans and legumes.
Supplements: Most people eating varied protein get enough; supplements are not needed for this role.
Connected topics
Open a group to see how each topic connects and how strong the evidence is.
Body parts (1)
- CellsEstablished role
Lysine is one of the amino acids the body uses to build proteins, which cells need for growth and repair. This is a normal food role, not a reason to take a supplement.
Functional actions (1)
- Cellular RepairEstablished role
As an essential amino acid, lysine is part of the protein supply the body uses for growth and tissue repair. Extra supplemental lysine has not been shown to speed repair in people who eat enough protein.
Root causes (1)
- Nutrient DeficiencyPreliminary or mixed
In one trial in poor households in Accra, Ghana, many people were at risk of low lysine intake and lysine supplements reduced some illness. This is one setting and does not apply to people eating varied protein.
Habits (1)
- Balanced NutritionEstablished role
Lysine must come from food, and it is richest in animal foods, soy, beans and legumes. A varied protein intake over the day matters more than any single supplement.
Documented risks and interactions (1)
- Stomach and bowel effects at high intakes. In a review of 71 human studies, side effects of oral L-lysine were mainly mild stomach and bowel symptoms such as nausea and diarrhoea.
Overview
Lysine is one of the nine essential amino acids. The body cannot make it, so it must come from food. [1] It is found in animal foods such as meat, milk, fish and eggs, and in plant foods such as soy, beans and legumes. [2] A food-composition review found that lysine generally occurs in low amounts in plant products and is enriched in animal products. [3] Lysine, together with methionine, is a starting material the body uses to make carnitine. [4] See essential amino acids for the group, carnitine for the compound, and vegan and vegetarian lysine intake.Health Canada's food-protein scoring pattern (for people aged 1 year and over) gives lysine as 51 mg per gram of protein; this is a yardstick for judging food protein, not a daily target. [5] A verified daily requirement for lysine from NIH ODS, EFSA, the NHS, MedlinePlus or Health Canada was not found, so none is quoted.
Most people who eat enough varied protein are unlikely to be short of lysine, but this depends on the diet. A trial in poor peri-urban households in Accra, Ghana found 30% of men, 50% of women and 15% of children at risk of lysine inadequacy. [6] That is one setting and should not be generalized to people who eat plenty of varied protein.
Lysine and cold sores: the focus question
Cold sores (herpes simplex labialis) are common, there is no cure, and they recur periodically. [7] The NHS advises asking a pharmacist, who can recommend creams, antiviral creams, and patches, and says to use antiviral cream when the early tingling starts, because it may not work after blisters appear. [8]| Question | What the source found | Evidence label |
|---|---|---|
| Does oral lysine prevent cold sores? | A 2015 Cochrane review of 32 randomized trials (2,640 immunocompetent people, 19 treatments) failed to find evidence of efficacy for lysine. [7] A narrative review of diet in skin conditions (2021, published 2023) reported L-lysine as effective for prophylaxis but not for shortening active lesions. [9] | Mixed; the Cochrane review is the more rigorous and found no evidence of efficacy |
| Prescription antivirals | The Cochrane review found long-term oral antiviral agents can prevent cold sores, but the clinical benefit is small. [7] | Different treatment, shown for comparison |
| Lysine for anxiety, or other uses | Proper evidence not found in the sources read (searched PubMed for lysine and herpes labialis; the other review read was a diet-in-dermatology review). | Insufficient evidence |
| Diarrhea and respiratory illness in a low-lysine-intake setting | In a double-blind randomized trial of 271 people in Accra, 1 g of lysine a day versus placebo reduced diarrheal illness in children and respiratory illness in men. [6] | Promising but limited; applies to a population with low lysine intake |
See the dedicated page: lysine and cold sores: what trials found. If you get frequent or severe cold sores, ask a clinician about options rather than relying on a supplement. The NHS says to see a GP if a cold sore has not started to heal within 10 days, is very large or painful, or if you have a weakened immune system. [8] Kissing a baby when you have a cold sore can lead to neonatal herpes, which is very dangerous to newborn babies. [8]
Related
Arginine and citrulline · Protein foundationsFrequently asked questions
Is lysine essential?
Yes. The body cannot make it. [1]
Does lysine prevent cold sores?
Evidence is mixed. A Cochrane review found no evidence of efficacy, while a narrower diet-in-dermatology review reported it as effective for prophylaxis but not for shortening lesions. [7][9]
What foods are high in lysine?
Animal foods such as meat, milk, fish and eggs, and plant foods such as soy, beans and legumes provide it, with animal products generally richer. [2][3]
How much lysine is too much?
No official upper limit exists. A systematic review estimated a provisional no-observed-adverse-effect level of 6,000 mg a day for adults, with stomach and bowel upset the main problem. [10]
Who should check with a clinician first?
People with kidney or liver disease, anyone pregnant or breastfeeding, and anyone taking prescribed medicines should ask a clinician or pharmacist, because the sources read did not describe lysine-specific safety for them.
More details: evidence, limits and cautions
The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.
Amounts and safety
A systematic review of 71 human studies of oral L-lysine added to an ordinary diet (doses from 16.8 to 17,500 mg a day, for 1 to 1,095 days) found adverse events were mainly gastrointestinal, such as nausea, stomachache and diarrhea, and estimated a provisional no-observed-adverse-effect level of 6,000 mg per person per day. [10] A separate review reported a no-observed-adverse-effect level of 6 g and a lowest-observed-adverse-effect level of 7.5 g a day for lysine in healthy adults. [11] These are research estimates, not official upper limits: national agencies have not set limits for individual amino acids, according to that review, and its studies were run under the initiative of a nonprofit amino acid science council. [11]
Check the amount per serving on the label (reading supplement labels) and be aware of duplicate ingredients across products (amounts and duplicate ingredients).
Who should ask first
- People with kidney disease or liver disease, who are pregnant or breastfeeding, or who take prescription medicines: the sources read did not describe lysine-specific interactions or precautions (Proper evidence not found; searched PubMed and MedlinePlus). Ask a pharmacist or clinician. See how interactions work, existing conditions and pregnancy and breastfeeding.
- Children: see children and teens.
- Before surgery: tell your surgical team about every supplement (supplements before surgery).
- Product quality: quality testing and certifications.
References
- MedlinePlus. Amino acids. National Library of Medicine, US. Review date 1/21/2025. Read 2026-10-22.
- MedlinePlus. Protein in diet. National Library of Medicine, US. Read 2026-10-22.
- Li P, He W, Wu G. Composition of amino acids in foodstuffs for humans and animals. Adv Exp Med Biol. 2021. Read 2026-10-22.
- Almannai M et al. Carnitine inborn errors of metabolism. Molecules. 2019. Read 2026-10-22.
- Health Canada. Dietary reference intakes tables: Reference values for macronutrients. Government of Canada, page dated 2025-11-19. Read 2026-10-22 through a web-fetch tool that summarised the page; rows as reported by that tool.
- Ghosh S et al. Effect of lysine supplementation on health and morbidity in subjects belonging to poor peri-urban households in Accra, Ghana. Am J Clin Nutr. 2010. Read 2026-10-22.
- Chi CC et al. Interventions for prevention of herpes simplex labialis (cold sores on the lips). Cochrane Database Syst Rev. 2015. Read 2026-10-22.
- NHS. Cold sores. National Health Service, England. Read 2026-10-22.
- Jamgochian M et al. Diet in dermatology: review of diet's influence on rosacea, hidradenitis suppurativa, herpes labialis, and vitiligo. Am J Lifestyle Med. 2023. Read 2026-10-22.
- Hayamizu K et al. Safety assessment of L-lysine oral intake: a systematic review. Amino Acids. 2019. Read 2026-10-22.
- Elango R. Tolerable upper intake level for individual amino acids in humans: a narrative review of recent clinical studies. Adv Nutr. 2023. Read 2026-10-22.