We use essential cookies (authentication, your saved goals/stack) by default. With your permission we’ll also enable privacy-respecting analytics (Vercel Web Analytics, anonymous load-time metrics) and error-replay diagnostics (Sentry — DOM snapshots only when an error fires) so we can fix bugs faster. Learn more about cookies
L-Lysine
Competes with arginine, which the cold-sore virus needs. Small, older trials suggest fewer outbreaks. Also a building block for collagen.
What the evidence says
L-Lysine appears to help in 4 of 4 studies with measurable effects — the evidence leans clearly favourable.
Most evidence is from high-quality meta-analyses and randomised trials published 1969–2026 with a typical study size of 50 participants.
Based on 55 studies · 2 meta-analyses · 47 RCTs · 5,436 total participants
Confidence
High confidenceWhat the studies found
By outcome
Rates a Moderate 5.5 because RCTs support cold-sore reduction at higher doses and lysine-arginine trials lower anxiety/cortisol, but herpes effects depend on dosing and calcium-absorption data are weak.
43 randomised trials
every one checked individually
Every randomised or controlled trial of L-Lysine indexed in PubMed, not a hand-picked subset. Meta-analyses and systematic reviews are deliberately excluded from this count: most of them cover many compounds at once, so counting them would inflate it.
PubMed · as of Jul 2026
35 trials ongoing or recruiting · 117 completed on ClinicalTrials.gov
35 of the completed trials have posted results
Registered trials show research momentum for L-Lysine, not proof of effect — a registration is a plan, and posted results are sponsor-reported, not peer-reviewed. They are never counted toward the evidence rating above.
Browse these trials on ClinicalTrials.govClinicalTrials.gov · as of Oct 2026
Under EU law (Reg. 1924/2006), EFSA reviews whether a specific health claim for L-Lysine meets the evidence standard. These are independent regulatory decisions on claims — not studies, and never counted toward the evidence score above.
Not authorised by EFSA
“L-Lysine Lysine can contribute to the development and maintenance of the normal structure of bones”
“Not authorised” means the specific claim wording did not meet the EU’s evidence standard — often a matter of dossier or phrasing, not proof of no effect. EFSA judges marketing claims and is kept separate from our study-based evidence score.
Source: EU Register of nutrition and health claims (European Commission / EFSA) · register snapshot Feb 2013
L-Lysine is an essential amino acid that must be obtained from diet or supplements. It's a key building block for collagen synthesis and plays important roles in immune function, calcium absorption, and hormone production.
Lysine is best known for its ability to prevent and reduce cold sore outbreaks by competing with arginine, which HSV needs to replicate. It's often deficient in vegetarian diets as grains are low in lysine.
Competes with arginine to inhibit HSV
Essential for collagen production
Enhances calcium uptake
How L-Lysine works — from molecular targets to health outcomes. Click an edge to see supporting research.This visualization is in beta — pathways are being refined and expanded.
Well-studied for HSV prevention; effective at 1-3g/day
May need supplementation as grains are low in lysine
May enhance calcium absorption
Tip: Take with food if needed; reduce dose
Tip: Reduce dose
L-Lysine has an evidence score of 5.5/10 — moderate evidence based on 54 indexed studies, including 1 meta-analysis. Competes with arginine, which the cold-sore virus needs. Small, older trials suggest fewer outbreaks. Also a building block for collagen. Representative study: PMID 39026098.
The commonly studied dose of L-Lysine is 500-3000mg daily; higher for active outbreaks. Individual needs vary — start at the lower end of the range and adjust based on how you respond.
The best time to take L-Lysine is between meals. It can be taken on an empty stomach. L-lysine is an essential amino acid that competes with L-arginine for absorption via the shared y+ cationic amino acid transporter system in the intestine.
L-Lysine is generally well-tolerated and considered safe for most healthy adults at recommended doses. Reported side effects are uncommon and include GI upset, diarrhea. Use caution if any of these apply to you: Lysinuric protein intolerance (rare genetic disorder).
Whey Protein
Likely helpsComplete protein with high leucine content that maximizes muscle protein synthesis.
Taurine
Too few graded studiesConcentrated in heart, brain, and muscle — best-supported for cardiovascular and metabolic health, with modest endurance benefits and emerging (mostly animal) longevity data.
Glycine
Too few graded studies3g before bed may improve subjective sleep quality and next-day alertness in small trials — also a building block for glutathione and collagen.
EAAs
Too few graded studiesComplete essential amino acid blend that maximizes muscle protein synthesis — superior to BCAAs alone.
Explore: Best supplements for Vitality & LongevityBest supplements for Focus, Memory & MoodBest supplements for Body Health
Reviewed by Dr. Baher Al Hakim · Last reviewed May 2026 · evidence from 55 studies · how we score · editorial policy
This information is for educational purposes only. It is not a substitute for professional medical advice. Always consult a qualified healthcare provider before starting, stopping, or changing any supplement or medication.
Tap node to isolate • Pinch to zoom • Tap edge for research