NutriDex

The Supplement Research Compendium
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L-Lysine

Essential amino acid taken to blunt recurrent cold sores.

Mixed evidence 🛡️Gut & Immune

✚ Updated · How we grade evidence

Evidence tier
Mixed
Research weight
Citations
8 verified / 8
Classification
Gut & Immune
❝
What the evidence says. Graded mixed: lysine is an essential nutrient with a plausible antiviral mechanism (competing with arginine, which HSV needs), and a few small double-blind RCTs found fewer/milder outbreaks at ≥1 g/day — but several equally rigorous trials found no benefit, doses below 1 g/day consistently fail, and no modern adequately powered trial settles it. (Mixed evidence: Conflicting results across studies; benefit uncertain.)

What is L-Lysine?

L-Lysine is a gut and immune supplement used for fewer cold-sore (herpes) recurrences. NutriDex grades the human evidence as Mixed. L-Lysine is an essential amino acid the body cannot make, obtained from meat, fish, eggs and legumes. It is marketed mainly to prevent and shorten cold sores (herpes simplex labialis), on the theory that lysine antagonises arginine, an amino acid the virus depends on. The human trials are genuinely split: in a 6-month placebo-controlled trial, 1,000 mg three times daily produced about 2.4 fewer outbreaks per year with milder, faster-healing lesions; a crossover study at ~1,250 mg/day also cut recurrences, while 624 mg/day did not. Yet other double-blind trials at lower doses found no effect, and reviewers note doses under 1 g/day generally fail. Beyond herpes, small studies suggest lysine (often combined with arginine) may modestly lower anxiety and salivary cortisol, and it improves intestinal calcium absorption. None of these uses rests on large, modern, confirmatory trials.

Purported Benefits

✓Fewer cold-sore (herpes) recurrences
✓Milder, faster-healing outbreaks
✓May lower stress/anxiety
✓Aids calcium absorption

Evidence by outcome

The same supplement can be well-proven for one use and unproven for another — here is the human evidence graded outcome by outcome.

OutcomeEvidenceEffectStudies
Cold-sore (HSV) recurrence frequencyDoses >=1 g/day cut recurrences in several RCTs, but <1 g/day trials failed; evidence genuinely split. Mixed ↔ mixed · moderate 4
Cold-sore severity & healing timeHigh-dose trial reported milder/faster-healing lesions, but a crossover RCT found no change in healing time. Preliminary ↔ mixed · small 2
Anxiety & stress / cortisolTwo RCTs (lysine often with arginine) lowered anxiety and cortisol; small and not independently confirmed. Preliminary ↑ benefit · small 2
Intestinal calcium absorptionSingle small trial showed increased calcium absorption and reduced urinary loss; no modern confirmation. Preliminary ↑ benefit · small 1

Dosing & Compounds

Typical Dose
1,000 mg three times daily (≥3 g/day) for prophylaxis of recurrent herpes labialis; lower doses (<1 g/day) appear ineffective unless paired with a low-arginine diet.
Active Compounds
L-Lysine (free base)L-Lysine monohydrochloride

Safety & Cautions

L-Lysine is generally well tolerated; high doses can cause diarrhoea, nausea and abdominal cramps. Because it shares renal transport with arginine and is cleared by the kidneys, people with kidney disease should avoid supplements, and very high intakes have been linked to Fanconi-type renal effects in case reports. Theoretical concerns exist for those with cardiovascular or gallbladder disease (possible cholesterol/atherogenic effects in animals). It may enhance calcium absorption, so use caution if you are also taking calcium supplements; no major drug interactions are well established. Educational only — always check with your doctor or pharmacist before combining L-Lysine with any medicine.

Key Studies

Systematic review Mailoo & Rampes 2017 ✓ PubMed
Review: lysine <1 g/day ineffective without a low-arginine diet; doses >3 g/day improve subjective disease experience; better trials needed.
RCT Griffith 1987 ✓ PubMed
1,000 mg L-lysine 3×/day for 6 months gave 2.4 fewer HSV recurrences/year with milder, faster-healing lesions vs placebo (p<0.05).
RCT DiGiovanna 1984 ✓ PubMed
Double-blind RCT of 400 mg lysine 3×/day found no benefit on frequency, duration or severity of recurrent herpes simplex.
RCT Thein 1984 (McCune) ✓ PubMed
Crossover RCT: 1,248 mg/day cut recurrence rate and severity; 624 mg/day was ineffective; neither dose shortened healing time.
RCT Milman 1980 ✓ PubMed
Double-blind crossover prophylaxis study reported fewer herpes labialis recurrences during lysine vs placebo periods.
RCT Smriga 2007 ✓ PubMed
DB-RCT (n=108): 2.64 g lysine + 2.64 g arginine/day for 1 week lowered trait and state anxiety and basal salivary cortisol in men.
RCT Smriga 2004 ✓ PubMed
DB-RCT of lysine wheat fortification in Syria reduced trait anxiety in men and the cortisol stress response in women over 3 months.
RCT Civitelli 1992 ✓ PubMed
In healthy and osteoporotic women, L-lysine increased intestinal calcium absorption and reduced urinary calcium loss.
8 sources cited · 8 verified Search all studies on PubMed ↗

Common questions about L-Lysine

What is L-Lysine used for?

L-Lysine is most often taken for Fewer cold-sore (herpes) recurrences, Milder, faster-healing outbreaks, May lower stress/anxiety, Aids calcium absorption. Essential amino acid taken to blunt recurrent cold sores.

Does L-Lysine work — what does the evidence say?

Mixed evidence. Conflicting results across studies; benefit uncertain. L-Lysine is an essential amino acid the body cannot make, obtained from meat, fish, eggs and legumes. It is marketed mainly to prevent and shorten cold sores (herpes simplex labialis), on the theory that lysine antagonises arginine, an amino acid the virus depends on. The human trials are genuinely split: in a 6-month placebo-controlled trial, 1,000 mg three times daily produced about 2.4 fewer outbreaks per year with milder, faster-healing lesions; a crossover study at ~1,250 mg/day also cut recurrences, while 624 mg/day did not. Yet other double-blind trials at lower doses found no effect, and reviewers note doses under 1 g/day generally fail. Beyond herpes, small studies suggest lysine (often combined with arginine) may modestly lower anxiety and salivary cortisol, and it improves intestinal calcium absorption. None of these uses rests on large, modern, confirmatory trials.

What is the typical dose of L-Lysine?

1,000 mg three times daily (≥3 g/day) for prophylaxis of recurrent herpes labialis; lower doses (<1 g/day) appear ineffective unless paired with a low-arginine diet.

Is L-Lysine safe? Any cautions or side effects?

L-Lysine is generally well tolerated; high doses can cause diarrhoea, nausea and abdominal cramps. Because it shares renal transport with arginine and is cleared by the kidneys, people with kidney disease should avoid supplements, and very high intakes have been linked to Fanconi-type renal effects in case reports. Theoretical concerns exist for those with cardiovascular or gallbladder disease (possible cholesterol/atherogenic effects in animals). It may enhance calcium absorption, so use caution if you are also taking calcium supplements; no major drug interactions are well established.

How many studies support L-Lysine?

NutriDex cites 8 sources for L-Lysine, graded "Mixed".

Cite this page
APA

Peh, D. (2026). L-Lysine: Benefits, Dosage, Side Effects & Evidence. NutriDex — The Supplement Research Compendium. Retrieved 26 Jun 2026, from https://nutridex.info/s/l-lysine

BibTeX
@misc{nutridex_l_lysine,
  author       = {Peh, Daryl},
  title        = {L-Lysine: Benefits, Dosage, Side Effects \& Evidence},
  year         = {2026},
  howpublished = {NutriDex --- The Supplement Research Compendium},
  url          = {https://nutridex.info/s/l-lysine},
  note         = {Reviewed by Dr Daryl Peh, MBBS Singapore, MMed FM. Accessed 2026-06-26}
}

For medical claims, citing the underlying primary studies linked above is preferred. NutriDex is an educational reference, not medical advice.

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