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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.

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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.

How to take it

TimingDivided doses across the day.
With food?On an empty stomach for best absorption, since dietary protein supplies competing amino acids.
Worth knowingDoses under 1 g/day have failed consistently in cold sore trials, so a 500 mg capsule once daily is not a smaller version of the studied protocol.

Interactions

With other supplements

  • L-arginine

    Lysine and arginine compete for the same intestinal and renal transporters, so each reduces the other's absorption — this competition is the basis of lysine's antiviral rationale. separate by at least 2 hours if you take arginine or citrulline for vascular reasons

  • calcium

    Lysine increases calcium absorption, which matters only if you are already at the upper end of calcium intake. no action needed unless you have hypercalcaemia

Well-established interactions only — this is not a complete list. Always tell your doctor and pharmacist what you take.

Frequently asked questions

Does lysine prevent cold sores?

The evidence is limited and largely negative: a Cochrane review found lysine did not significantly reduce cold sore recurrence. Some small trials at 3 g/day reported fewer outbreaks, but they were methodologically weak.

How much lysine should I take for cold sores?

Studies used 1–3 g/day of L-lysine, with the few positive results at 3 g/day. Doses below 1 g/day have consistently failed, so a 500 mg capsule is not a smaller version of the studied protocol.

Is L-lysine safe?

L-lysine is generally well tolerated, with abdominal pain and diarrhea at multi-gram doses. Case reports link high-dose lysine to kidney problems, so avoid it or use it only under supervision in chronic kidney disease.

Scientific references

Where to buy

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

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