Know2eat

L-lysine

Amino Acids & Proteins

What l-lysine may help with

Ranked by how strong the human evidence is — best supported first.

Best supportedImmune functionLimited evidence· 3 sources

Then, in order

3 things to know first — allergies, interactions and limits

About L-lysine

An essential amino acid abundant in animal protein and legumes and limiting in cereal grains. It is required for collagen cross-linking and carnitine synthesis.

Lysine is sold almost entirely for cold sores, on a specific and testable idea: herpes simplex replication depends on arginine, and lysine competes with arginine for the same transporter, so raising the lysine-to-arginine ratio should suppress it. The trials are old, small and inconsistent — some report fewer or shorter outbreaks at 1–3 g/day, others find nothing, and a systematic assessment concluded the evidence did not support a benefit at doses under 3 g/day. It remains one of the more plausible thin claims in this catalogue: a defensible mechanism attached to a literature that never got properly done.

Sold as
Capsule, Tablet, Powder, Topical cream
Standardised to
mg L-lysine; the hydrochloride salt contains about 80% lysine by weight — a product without this marker may not resemble what was studied.
Also known as
Lysine, L-lysine HCl

Regulation: Sold as a dietary supplement with no pre-market efficacy review. Also used as a feed additive and food fortificant in cereal-based diets where lysine is the limiting amino acid.

What the research used

The amounts, forms and durations published trials of L-lysine actually administered.

These are the amounts published trials administered — not a recommendation, and not a dose to copy. Trial participants were screened, supervised and given a characterised preparation. What is in a retail bottle is frequently not what was studied, and the amount that suits one person is not general advice.

  • Studied for Recurrent herpes labialis

    1–3 g

    Limited

    L-lysine daily, divided · 6–12 months in prevention trials

    Trials report inconsistent results, with a suggestion that doses below 3 g/day are ineffective. Most of this literature dates from the 1980s and would not meet current standards.

This is general information about food, not medical advice. It cannot diagnose, treat or replace guidance from a clinician who knows your history.

When it was taken

Each window says whether a trial compared it against an alternative, or whether it is convention and pharmacology. Most timing advice is the second kind.

None of the timings below were directly compared in a trial. They reflect how the research happened to dose, or what the pharmacology implies — which is not the same as a timing being better.

  • On an empty stomach

    Not enough

    Often taken away from protein meals so that dietary arginine does not compete for the same transporter. This follows from transport pharmacology rather than from a tested trial comparison.

    Timing was not directly compared. This reflects convention or how the compound behaves in the body, not a trial showing this window works better.

The evidence in depth

Best supported: Limited

What each association actually rests on, and the papers behind it. A rating describes the state of the research, not how promising the supplement sounds. How we rate evidence.

Immune function

Immune Health
Limited evidence

Trials of lysine for recurrent cold sores report reduced frequency or severity in some studies and no effect in others, with a review concluding that doses below 3 g/day were not supported. The mechanism is plausible and the evidence never became convincing.

What may be going on: Herpes simplex replication is arginine-dependent, and lysine competes with arginine for the same amino acid transporter, lowering intracellular arginine availability.

Limited evidence. Early human work, or mostly lab and animal research.

View the 3 sources

Deep research mode adds each paper’s own conclusion and stated limitations.

Bone mineral density

Bone Health
Not enough evidence

Lysine is required for collagen cross-linking and has been reported to increase calcium absorption in small studies. There is not enough human research to support a bone claim.

Not enough evidence. Not enough human research to say anything useful yet.

View the 1 source

Deep research mode adds each paper’s own conclusion and stated limitations.

Stress and anxiety

Mental Wellbeing
Not enough evidence

A trial fortifying wheat with lysine in a population with low lysine intake reported reduced anxiety scores. That is a deficiency-correction finding in a specific setting and does not extend to supplementation in well-fed populations.

Not enough evidence. Not enough human research to say anything useful yet.

View the 2 sources

Deep research mode adds each paper’s own conclusion and stated limitations.

Things to know

Interactions, contraindications and dose limits, most serious first. Concentrated extracts interact with medication in ways the whole plant does not, so this section carries more weight here than it does on a food page.

  • Interaction

    Calcium absorption and aminoglycoside antibiotics

    Interacts withCalcium supplements, aminoglycoside antibiotics

    Lysine has been reported to increase calcium absorption, which matters for anyone already taking calcium supplements. High doses alongside aminoglycoside antibiotics have been flagged as a theoretical nephrotoxicity concern.

  • Worth knowing

    Kidney disease

    High-dose amino acid supplementation raises nitrogen load. Case reports describe kidney problems with very high lysine intake, and it is not appropriate in existing renal impairment without advice.

  • Too much

    Digestive upset

    Abdominal cramping and diarrhoea occur at multi-gram doses.

Evidence ratings on this page: 1 limited evidence, 2 not enough evidence.

Supplements are sold in the US without pre-market review of efficacy or safety. Nothing on this page is a recommendation to take L-lysine, or a dose to follow.