L-Lysine
A coherent mechanism and a dose-dependent hint for cold sores, untested at modern standards since the seventies.
C-
Evidence grade
C-
Worth it
$8-14/month
Typical cost
DoseRequirement is met by any protein-adequate diet. The prophylaxis literature uses 1,000 to 3,000 mg/day of L-lysine between outbreaks; below 1 g/day the trials show nothing, which makes the common 500 mg capsule a dose the evidence does not cover. Lysine and arginine compete, so high-dose arginine supplementation (see its record) works against this use.
BasisLysine has a plausible mechanism, a dose-dependent signal in small old trials, and forty years without a definitive test.
L-lysine is an essential amino acid sold almost entirely for one purpose: preventing herpes simplex cold sores, by antagonizing arginine. We grade L-Lysine C- on evidence and C- for worth-it at about $8-14 per month.
What it does
L-lysine is an essential amino acid sold almost entirely for one purpose: preventing herpes simplex cold sores, by antagonizing arginine. It is also a collagen building block, a claim that belongs to dietary protein generally and earns nothing here.
What the research says
May reduce cold sore recurrence at doses of 1 g/day and above; the trial file is old and mixed
Evidence: emerging. Lysine competes with arginine, which herpes simplex uses to replicate, a clean mechanism tested in small trials from the 1970s onward. Reviews (Chi 2015) conclude prophylaxis at 1 g/day or more shows a recurrence-reduction signal while doses under 1 g do not, and acute treatment of an active outbreak shows nothing. Trial quality is low throughout and no large modern trial exists, but the pattern (dose-dependent prevention, no treatment effect) is at least coherent with the mechanism.
Lysine has a plausible mechanism, a dose-dependent signal in small old trials, and forty years without a definitive test. That combination earns C-: more than folklore, less than established, and cheap and safe enough that the many people who swear by it are not obviously wasting anything but money's smallest denomination.
Is it worth it?
Evidence (C-) sits below the leaderboard floor, so the worth-it grade is capped at C+ however inexpensive it is; the derived value lands at C-. About $11 a month at prophylaxis doses. Derived from the October 2026 worth-it model.
Typical cost
$8-14/month
Common form, not a brand recommendation
Dosage context established
Requirement is met by any protein-adequate diet. The prophylaxis literature uses 1,000 to 3,000 mg/day of L-lysine between outbreaks; below 1 g/day the trials show nothing, which makes the common 500 mg capsule a dose the evidence does not cover. Lysine and arginine compete, so high-dose arginine supplementation (see its record) works against this use.
Worth-it leaderboard
L-Lysine sits outside the worth-it top 20.
L-Lysine sits outside the current top 20 on the gated leaderboard. The leaders below clear an evidence floor of B- before price counts at all, so cheap alone never earns a rank.
- 1AWorth itCreatine evidence A-~$5-10/mo
- 2AWorth itCaffeine evidence B+~$5-10/mo
- 3AWorth itVitamin D evidence B~$5-8/mo
See the full worth-it leaderboard →
When the evidence moves a grade, this ranking moves with it. Thursday is where you hear it first.
Safety notes
Well tolerated at studied doses; GI upset at high intakes. Lysine in large amounts is a consideration in kidney disease, where amino acid loads are managed clinically. It is not a treatment for an active outbreak and is not a substitute for antiviral therapy in frequent or severe herpes, where suppressive antivirals have the strong evidence.
Longevity Lab Report
L-Lysine news. Graded when it happens.
The grade on this page stays free. The email carries the news on l-lysine: expert moves, dose changes, and what is working, in plain English every Thursday.
Changelog
Last updated 2026-10-23
- 2026-10-23|Graded from the herpes prophylaxis trial literature and its reviews. The record is candid that the evidence predates modern trial standards and has never been re-tested at scale, which is itself information about the claim's commercial and scientific priority.
- 2026-10-23|Not listed under any goal: cold sore recurrence does not map onto the library's ten goals.
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