An essential amino acid used to reduce cold sore outbreaks — evidence is mixed but reasonably consistent at higher doses.
TrustedSupp Tier System™ · Tier 3Take as a defined course
Check before you startThis one has documented interactions with medication classes where the consequences are serious. If you take any prescription medicine, run it past a pharmacist before starting.
Evidence strength
38/100Limited
WEAKLIMITEDMODERATESTRONGVERY STRONG
What the evidence supports: reducing recurrence of cold sores at higher doses, in mixed-quality trials.
This scores how well-supported the claim above is — not how much benefit you personally would get. A high score on a narrow claim does not extend to everything the product is marketed for.
How long to take it
Ongoing during outbreak-prone periods, or as needed.
Who it's actually for
People with recurrent cold sores, alongside — not instead of — antiviral treatment.
Safe upper limit
Unverified
No formal upper limit; up to 3 g daily is common in trials
Generally well tolerated. It increases calcium absorption. Rare kidney problems have been reported, so avoid with kidney disease unless your doctor agrees.