L-Lysine
L-Lysine
TL;DR
L-Lysine is an essential amino acid best known for cold-sore (HSV-1) prevention, where evidence is genuinely mixed: some trials show fewer recurrences at 1-3 g/day, others show no benefit. It is safe and cheap, but the arginine-antagonism theory outperforms the clinical data.
Ideal For
- People with frequent HSV-1 cold-sore recurrences willing to try a low-risk option
Avoid If
- You have kidney disease (high-dose amino acids)
- You are pregnant/breastfeeding at high doses (insufficient data)
- You expect it to treat an active outbreak (evidence is weakest there)
Frequently Asked Questions
Overview
L-Lysine is an essential amino acid abundant in meat, fish and legumes. The cold-sore rationale is mechanistic: herpes simplex virus replication requires arginine, and lysine competes with arginine for intestinal absorption and cellular uptake, lowering the arginine:lysine ratio. Clinical trials from the 1970s-80s (Griffith et al.) suggested 1,000 mg/day reduced recurrence frequency, with higher doses (~3 g) needed in some studies; however, later rigorous reviews found inconsistent results and many trials were small and short. Prophylaxis appears more plausible than treating active lesions, where evidence is weakest. Lysine also has a physiological role in calcium absorption and carnitine synthesis; deficiency is rare outside of low-protein diets. A small trial suggested lysine (with arginine) may blunt stress-induced cortisol responses, but this is preliminary. Overall: reasonable to try for frequent cold sores, low risk, but expectations should be modest.
How It Works
- Competes with arginine for intestinal absorption and cell transport
- HSV-1 requires arginine for replication - lower arginine:lysine ratio may suppress viral activity
- Precursor for carnitine synthesis and collagen cross-linking
- Supports intestinal calcium absorption
Benefits & Outcomes
No linked outcomes yet. Research is ongoing.
Health Concerns Addressed
No linked health concerns yet.
Supporting Research6 studies
Interventions for prevention of herpes simplex labialis (cold sores on the lips)
Chi CC, Wang SH, Delamere FM
Evidence for oral lysine in preventing recurrent herpes labialis was of low quality and did not demonstrate a clear preventive effect.
Failure of lysine in frequently recurrent herpes simplex infection: treatment and prophylaxis
DiGiovanna JJ, Blank H
Lysine hydrochloride did not reduce the rate, duration or severity of recurrent herpes simplex episodes compared with placebo.
Lysine for Herpes Simplex Prophylaxis: A Review of the Evidence
Mailoo VJ, Rampes S
Doses of at least 3 g/day were associated with benefit in some trials, while lower doses were consistently ineffective.
Success of L-lysine therapy in frequently recurrent herpes simplex infection: treatment and prophylaxis
Griffith RS, Walsh DE, Myrmel KH
L-lysine 3 g/day reduced the recurrence frequency of herpes simplex episodes compared with placebo.
Oral treatment with L-lysine and L-arginine reduces anxiety and basal cortisol levels in healthy humans
Smriga M, Ando T, Akutsu M
Combined L-lysine and L-arginine reduced trait anxiety and basal salivary cortisol in healthy adults.
Dietary L-lysine and calcium metabolism in humans
Civitelli R, Villareal DT, Agnusdei D
L-lysine supplementation increased intestinal calcium absorption and reduced urinary calcium excretion.
Safety Information
Potential Side Effects
GI upset and diarrhoea at high doses (>10 g/day); gallstones reported in one case series at very high chronic doses.
Contraindications
Lysinuric protein intolerance; severe renal impairment.
Drug Interactions
- Aminoglycoside antibiotics (theoretical renal risk)
- Calcium supplements (lysine increases calcium absorption)
Pregnancy & Breastfeeding
Pregnancy: insufficient_data
Breastfeeding: insufficient_data
Dosage Guidelines
Dosage Used in Studies
1000-3000 mg
Best Time to Take
Divided daily doses
Best Form
Plain L-lysine HCl capsules or powder
Dosing by Goal
| Goal | Dose | Notes |
|---|---|---|
| 1000 mg/day (up to 3000 mg) | Evidence strongest for prophylaxis, not acute treatment | |
| ~30-38 mg/kg/day from diet + supplements | Rarely needed with adequate protein |
Forms Compared
Standard 500-1000 mg units
Economical for higher doses
Food & Timing
Absorption is competitive with other amino acids; empty stomach theoretically preferable.
Medical Disclaimer
The information provided on this website is for educational and informational purposes only and is not intended as a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition or before starting any supplement regimen.
Individual results may vary. The statements on this website have not been evaluated by the Food and Drug Administration. Products and information are not intended to diagnose, treat, cure, or prevent any disease.