L-lysine (recurrent herpes simplex prophylaxis)
Essential amino acid with small RCT signal for reducing recurrence of cold sores at 1–3 g/day.
Why
L-lysine is an essential amino acid that competes with arginine for cellular uptake. Several small RCTs (Griffith 1981, Thein 1984, McCune 1984) report reduced frequency, severity and duration of recurrent herpes simplex labialis at 1–3 g/day daily prophylaxis. The Mailoo 2017 systematic review noted methodological limitations but a directionally consistent signal. Most useful as ongoing prophylaxis rather than acute treatment.
How it works
Competes with arginine, which HSV requires for viral replication, for cellular uptake via the cationic amino acid transporter (CAT-1). Lowering intracellular arginine availability slows viral protein synthesis.
Expected onset · Prophylactic effect over weeks; acute outbreak management at first prodromal symptom
How to take
Dosage
Prophylaxis: 1 g three times daily continuously. Outbreak rescue: 3 g/day at first symptom for 7–10 days.
Timing
Divided throughout the day, away from arginine-rich foods (nuts, chocolate, seeds, gelatin) at the same meal
On the label
'L-lysine HCl' with stated grams per dose. Some users pair with reduced dietary arginine for outbreak prophylaxis.
Ideal for
Adults with recurrent herpes simplex labialis (≥6 episodes per year) seeking nutrient-based prophylaxis as adjunct to or alternative to pharmacological acyclovir.
Safety
Evidence
Griffith 1987 RCT (n=41 recurrent HSV): L-lysine 1,000 mg three times daily significantly reduced outbreak frequency vs placebo over 6 months. Mailoo 2017 review noted directionally positive signal across small trials with limited methodological quality. Preliminary, RCTs exist in non-tier-1 journals but are small or short-duration. No Cochrane review, EMA monograph or EFSA-authorised claim covers the indication.
Preliminary, RCTs exist in non-tier-1 journals but are small or short-duration. No Cochrane review, EMA monograph or EFSA-authorised claim covers the indication.
- Griffith et al., Dermatologica 1987, success of L-lysine therapy in frequently recurrent herpes simplex infection (RCT, n=41)
- Thein & Hurt, Oral Surg Oral Med Oral Pathol 1984, lysine as a prophylactic agent in the treatment of recurrent herpes simplex labialis (RCT)
- Mailoo & Rampes, Integr Med 2017, lysine for herpes simplex prophylaxis: a review of the evidence
Where to get it
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