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L-lysine: how much to take

L-lysine is an essential amino acid. It is sold mainly to prevent cold sores (herpes simplex).

Calculator Official intake Study doses Best form Safety Sources

Adults 18+ only
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Official daily intake

This is not an essential nutrient, so there is no official daily intake. Only study doses are shown.

Doses used in studies

These are doses tested in research, not personal advice. Some exceed the upper limit because they were short courses or given under medical care.

Weak evidenceWeak: one small trial, pilot data or results that conflict.Based on 1 randomised trial, 1 review or position paper. 1 finding disagrees.How grades work

Fewer cold sore outbreaks

3 g a day

In a 6-month trial (52 people completed), 1 g lysine three times a day gave about 2.4 fewer outbreaks, milder symptoms and faster healing than placebo. A review concluded that doses under 1 g a day do not work and doses above 3 g a day seem to help.

Griffith RS et al. 1987 · Mailoo VJ, Rampes S 2017

Other findings

A trial of 1.2 g a day (400 mg three times a day) in 21 people found no benefit for treatment or prevention.

DiGiovanna JJ, Blank H 1984

Best form and why

No best form

Why: The trial used lysine monohydrochloride tablets giving 1 g lysine each. Count lysine content: lysine HCl is about 80% lysine.

Griffith RS et al. 1987

Forms and labels

  • Label shows L-lysine
  • L-lysine HCl, full weight (~80% lysine)

L-lysine HCl is about 80% lysine by its formula.

Food sources

Meat, fish, eggs, dairy, legumes. Most diets give plenty.

Interactions

No important interactions known.

Safety

People with heart or gallbladder disease should check with a doctor, according to the review.

Pregnant, breastfeeding, on medication, or managing a health condition? Check with a doctor or pharmacist before starting a supplement.

Sources

  1. Randomised trial Griffith RS et al. (1987). Success of L-lysine therapy in frequently recurrent herpes simplex infection: treatment and prophylaxis. Dermatologica 175:183-190
  2. Review / position paper Mailoo VJ, Rampes S (2017). Lysine for herpes simplex prophylaxis: a review of the evidence. Integr Med (Encinitas) 16:42-46
  3. Randomised trial DiGiovanna JJ, Blank H (1984). Failure of lysine in frequently recurrent herpes simplex infection: treatment and prophylaxis. Arch Dermatol 120:48-51

Values checked: November 12, 2026.

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