Lysine and Cold Sores: What Trials Found
Does lysine prevent or shorten cold sores? Trials from the 1970s and 1980s disagree, and a Cochrane review found no evidence of benefit. See the studies, safety and standard care.
Content last updated . This page has not been medically reviewed.
What cold sores are
Cold sores are caused by the herpes simplex virus (HSV). There is no cure; they usually go away on their own in a few weeks, and antiviral medicines can help them heal faster or help prevent them in people who get them often. [3] The NHS says they usually clear on their own within 10 days and are contagious from the first tingling until fully healed. [4]What the studies found
| Study | Who and what | Result | Label |
|---|---|---|---|
| Cochrane review of prevention (2015; searches to May 2015) | 32 randomized trials, 2,640 immunocompetent people, 19 treatments. Quality low to moderate for most outcomes. [2] | "We failed to find any evidence of efficacy for lysine." [2] | Insufficient evidence |
| Milman 1980 | 65 patients, double-blind crossover of lysine versus placebo. [5] | No effect on recurrence rate overall, though more patients were recurrence-free on lysine; no effect on healing rate. [5] | Mixed |
| DiGiovanna 1984 | 21 patients with frequent recurrences, double-blind, placebo-controlled. [6] | Unable to detect any substantial benefit as treatment or prevention. [6] | Insufficient evidence |
| Griffith 1987 | 27 on lysine and 25 on placebo completed a 6-month double-blind trial of 1,000 mg per dose three times a day (a study amount). [7] | Fewer infections, milder symptoms and shorter healing. [7] | Promising but limited (small, old) |
The trials used different amounts and designs, and all are small. The Cochrane review covers prevention only. We did not find a modern large trial of lysine for treating a cold sore that has already started: Proper evidence not found (searched PubMed for lysine and herpes labialis, and the Cochrane prevention review).
The "lysine to arginine" idea
The idea comes from laboratory work: in tissue culture, arginine deficiency suppressed herpes simplex virus replication, and lysine, an analog of arginine, antagonized arginine's growth-promoting action. [8] A recent review says the lysine-arginine antagonism still needs research in people. [9] We found no trial in the searches we ran showing that changing the lysine-to-arginine ratio in food prevents cold sores. This is preclinical reasoning.When a cold sore needs more than waiting
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 you have a weakened immune system. [4] Kissing a baby when you have a cold sore can lead to neonatal herpes, which is very dangerous for newborns. [4] The NHS also says a pharmacist can recommend antiviral creams to speed healing. [4]More on lysine: Lysine profile and Essential Amino Acids.
Frequently asked questions
Does lysine prevent cold sores?
A Cochrane review found no evidence of efficacy for lysine. [2] Small older trials disagree. [5][7]
Does lysine heal a cold sore faster?
One 1987 trial reported shorter healing time [7], while a 1984 trial found no substantial benefit. [6] We found no modern large trial.
Should I avoid arginine foods?
The idea comes from tissue-culture work. [8] We found no trial showing it prevents cold sores.
Is lysine safe?
A review says tested amino acids were well tolerated in relatively healthy adults. [10] Safety with medicines, pregnancy and kidney or liver disease is not described in the sources we read; ask a pharmacist.
What should I do for a cold sore?
Antivirals can help, per MedlinePlus. [3] See a GP if it is not healing in 10 days. [4]
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.
How to read the evidence labels
Labels used on this page: mixed, insufficient evidence, preclinical, Proper evidence not found.
Safety and who should ask first
- Tolerability. A 2023 review (based on studies organized by an amino acid industry nonprofit) says the amino acids tested were well tolerated in relatively healthy adults, and notes no national upper limits exist. [10]
- Medicines and conditions. Interactions, kidney or liver disease, pregnancy, breastfeeding and children are not described for lysine in the sources we read. Ask a clinician or pharmacist; see How interactions work and Pregnancy and breastfeeding.
- Surgery. Tell the team about supplements: Supplements before surgery.
- Quality. Quality testing and certifications.
References
- MedlinePlus Medical Encyclopedia. Amino acids. US National Library of Medicine. 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;(8):CD010095. PubMed 26252373.
- MedlinePlus. Cold Sores. US National Library of Medicine. Read 2026-10-22.
- NHS (UK). Cold sores. Page last reviewed 19 February 2024. Read 2026-10-22.
- Milman N, et al. Lysine prophylaxis in recurrent herpes simplex labialis: a double-blind, controlled crossover study. Acta Derm Venereol. 1980;60(1):85-7. PubMed 6153847.
- DiGiovanna JJ, Blank H. Failure of lysine in frequently recurrent herpes simplex infection. Arch Dermatol. 1984;120(1):48-51. PubMed 6419679.
- Griffith RS, et al. Success of L-lysine therapy in frequently recurrent herpes simplex infection. Dermatologica. 1987;175(4):183-90. PubMed 3115841.
- Griffith RS, DeLong DC, Nelson JD. Relation of arginine-lysine antagonism to herpes simplex growth in tissue culture. Chemotherapy. 1981;27(3):209-13. PubMed 6262023.
- Lysine: Sources, Metabolism, Physiological Importance, and Use as a Supplement. Int J Mol Sci. 2025;26(18):8791. PubMed 41009362.
- Tolerable Upper Intake Level for Individual Amino Acids in Humans: A Narrative Review of Recent Clinical Studies. Adv Nutr. 2023. PubMed 37062432.