Supplement analysis backed by scientific evidence · PT

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Limited evidenceImmunity

L-Lysine

Lysine for cold sores is one of the most persistent supplement beliefs with the least supporting evidence: a Cochrane review found no benefit for prevention, and the positive trials are small and contradictory.

What the science says

  • Cochrane found no evidence lysine prevents cold sores Limited evidence

    The Cochrane review of interventions for preventing herpes simplex labialis assessed lysine among other agents and found no significant reduction in recurrence versus placebo. This is the highest-quality synthesis available and it is negative.

  • Higher-dose trials are mixed and methodologically weak Limited evidence

    A narrative review of the lysine literature concluded that doses below about 1 g/day are consistently ineffective, while some trials at 3 g/day reported fewer or milder recurrences. Those trials had small samples, inconsistent outcome definitions and no dose-response confirmation, so the finding is hypothesis-generating rather than practice-changing.

  • Anxiety and stress claims come from a narrow evidence base Limited evidence

    The lysine-plus-arginine anxiety findings derive from a small number of trials, largely in populations with low dietary lysine intake, using combined amino acid doses around 2.6 g/day. They have not been replicated in well-nourished Western populations and should not be generalized.

Dosage & safety

Studied doseCold sore prevention studies used 1-3 g/day, with the few positive results clustered at 3 g/day; acute outbreak protocols have used up to 3 g/day in divided doses. Doses below 1 g/day have consistently failed.
SafetyGenerally well tolerated, with abdominal pain and diarrhea the main complaints at multi-gram doses. Lysine competes with arginine for absorption and renal reabsorption, which is the basis of both its antiviral rationale and a theoretical concern for people relying on arginine for vascular function. Case reports link high-dose lysine to renal dysfunction, and it should be avoided or supervised in chronic kidney disease. Lysine may increase calcium absorption, relevant for people with hypercalcemia. Avoid in people with lysinuric protein intolerance.

Scientific references

Where to buy

NOW Foods, L-Lysine, 1,000 mg, 100 Tablets

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