Lysine (L-Lysine)

What L-lysine; lysine is and how it works

L-lysine is an essential amino acid -- one the body needs but cannot make on its own, so it must come from food (meat, fish, dairy, eggs, legumes) or supplementation. It is genuinely NOT a regulated prescription or over-the-counter medicine in the United States, United Kingdom, European Union, or New Zealand -- it is sold and regulated as a food or dietary supplement in these markets. Canada is a real exception where L-lysine products can be licensed by Health Canada as Natural Health Products, and Australia is a real exception where L-lysine is an active ingredient in TGA-Listed complementary medicines. (1)

People most commonly take L-lysine supplements hoping to reduce cold sore (herpes labialis) outbreaks. Because it is 'just an amino acid', it is easy to assume it is automatically safe at any dose -- but the evidence for cold-sore prevention is genuinely mixed and depends heavily on dose, and there are real, documented safety cautions for people with certain heart, gallbladder, kidney, or liver conditions.

Mechanism of action: how L-lysine; lysine works

L-lysine is an essential proteinogenic amino acid required for protein synthesis, collagen formation, and calcium absorption, among other roles. Its proposed mechanism for reducing herpes simplex recurrence is competitive inhibition of arginine, an amino acid the herpes simplex virus uses for replication -- a plausible biological mechanism, though the clinical evidence for a meaningful antiviral effect at commonly used doses remains limited per the systematic review reviewed for this dossier. (1)

What L-lysine; lysine is used for

Before taking L-lysine; lysine

Do not take / not appropriate for

• There is no absolute contraindication described in the sources reviewed for this dossier, but caution is advised (see tell_your_clinician below) before starting supplementation if you have certain heart, gallbladder, kidney, or liver conditions. (all countries) (1)

Tell your clinician about

• If you have cardiovascular disease -- caution is advised with lysine supplementation.
• If you have gallstones, or a personal or family history of gallstones -- high lysine intake has been linked to gallstone formation and elevated cholesterol in animal studies.
• If you have kidney or liver problems -- caution is advised, and safe maximum doses have not been established for people with severe kidney or liver disease.
• If you have asthma or a condition affecting your immune system -- caution is advised.
• If you are pregnant, trying to conceive, or breastfeeding -- safe maximum doses have not been established for these groups.
• If you are considering giving lysine supplements to a young child -- safe maximum doses have not been established for young children.
• All other supplements and medicines you take, particularly other amino acid supplements, since high lysine intake may reduce absorption of arginine, another amino acid important for wound healing and blood vessel function.

How to take L-lysine; lysine

• There is no single regulator-set standard dose, since lysine is not a regulated drug in most markets -- follow the specific product's label directions or a clinician's/pharmacist's advice.
• If using lysine specifically for cold-sore prevention, be aware the evidence reviewed suggests doses below 1 g/day are unlikely to help unless combined with a low-arginine diet, while the higher doses (above 3 g/day) that showed more promise in one trial have not been extensively studied for long-term safety.
• If you are using a TGA-Listed Australian product marketed for cold-sore prevention, follow that specific product's own labelled directions.
• Discuss any planned high-dose or long-term use with a clinician or pharmacist first, particularly if you have any of the conditions listed above.

Procedures and treatment changes

Tell the treating team before surgery, procedures, or any medicine change. Do not alter treatment without the responsible clinician. (1) (2) (3) (4) (5)

Missed dose

Not applicable in the same way as a prescribed medicine, since lysine is a food/supplement product without a regulator-set dosing schedule in most markets. If you are following a specific product's dosing schedule, simply resume your normal schedule at the next planned dose.

Overdose

This dossier's sources did not describe a specific lysine overdose syndrome or established toxic dose threshold in humans, though animal studies have linked very high doses to kidney injury, elevated cholesterol, and gallstone formation. As with any supplement, taking substantially more than a product's labelled amount is not advised. If a large accidental ingestion occurs, especially in a child, or if any concerning symptoms develop, contact a doctor or poison control centre for guidance. (1)

Side effects

Side effects and their urgency vary; report severe, persistent, or concerning symptoms.

Serious warnings

Interactions

• Other amino acid supplements, particularly arginine: high lysine intake may reduce arginine absorption, since the two amino acids compete for absorption -- tell your clinician about any other amino acid supplements you take. (1)
• Calcium supplements: some study data suggest lysine may increase intestinal calcium absorption in the context of a low-protein diet -- discuss with your clinician if you take calcium supplements and are considering lysine.

Pregnancy, breastfeeding, kidney/liver function, age

Monitoring

Before starting

• Check whether you have cardiovascular disease, gallstones, kidney or liver problems, asthma, or an immune-system condition, given the documented cautions for these groups.
• Check whether you take other amino acid supplements, particularly arginine.

During treatment

• Watch for any signs of gallbladder problems or unexpected changes in cholesterol if using long-term or at high doses.
• Watch for any signs of kidney problems if using long-term or at high doses.
• Discuss with your clinician if using lysine for cold-sore prevention to confirm it is a reasonable complement to, not a replacement for, proven antiviral treatment where needed.

Storage

Store capsules, tablets, or powder as directed on the product label, typically in a cool, dry place. Keep out of reach of children, as with any supplement product.

Frequently asked questions

References

1. Singh BK, Bhalla AS (2018). Lysine for Herpes Simplex Prophylaxis: A Review of the Evidence (PMC6419779)PubMed Central (peer-reviewed systematic review) · United States (international evidence base) · accessed 2026-07-31 · source 1
2. L-lysine as a dietary ingredient -- FDA dietary supplement regulatory frameworkU.S. Food and Drug Administration -- dietary supplement regulatory framework (Dietary Supplement Health and Education Act, DSHEA, 1994) · United States · accessed 2026-07-31 · source 2
3. Natural Health Products licensing framework; L-lysine as a licensable NHP medicinal ingredientHealth Canada -- Natural Health Products framework and Licensed Natural Health Products Database (LNHPD) · Canada · accessed 2026-07-31 · source 3
4. L-lysine as an active ingredient in TGA-Listed (AUST L) complementary medicines, including 'Ethical Nutrients Lysine Cold Sore Defence' (ARTG 353838) and 'EZZ L-Lysine Growth Capsule' (ARTG 413522/476307)Australian Therapeutic Goods Administration (TGA), Australian Register of Therapeutic Goods (ARTG) · Australia · accessed 2026-07-31 · source 4
5. Dietary Supplements Regulations 1985 -- amino acids (including lysine) as a permitted dietary supplement categoryNew Zealand Ministry for Primary Industries (MPI) / Medsafe -- Dietary Supplements Regulations 1985 (made under the Food Act 2014) · New Zealand · accessed 2026-07-31 · source 5

Brand names by country

Single-ingredient L-lysine; lysine names are shown separately by country. Product availability, strengths, and supply rules can change; combination products are not included here.

Priority countries