What L-Lysine is
L-Lysine (lysine) is one of the nine essential amino acids — protein building blocks the body cannot make on its own and must obtain from food, according to MedlinePlus. It is naturally present in protein-rich foods such as meat, fish, eggs, dairy, and legumes, and it is also sold as a single-ingredient dietary supplement.
Commonly used for
Taken as a supplement by people seeking additional dietary lysineUsed by some people for recurring cold sores (oral herpes), though this use is not established by the authoritative sources reviewedUsed by some people on plant-based diets, where dietary lysine intake may be lowerMarketed for general immune or skin/collagen support, though such benefits are not confirmed by the sources reviewed
What the evidence shows
Authoritative US government sources confirm only that lysine is an essential amino acid needed for normal protein function; they do not establish that lysine supplements treat or prevent any specific condition. The single source reviewed here is a general MedlinePlus amino-acids encyclopedia entry rather than a lysine-specific health-topic page, so it does not address popular supplement uses such as cold sores, and those claims are not supported by it. Most healthy people in the US obtain enough lysine from a typical diet.
Typical dosage
No US government dietary-supplement dose has been established for L-Lysine in the source reviewed; healthy people generally meet their needs through food, and commercial supplement labels vary widely (often listing roughly 500–1,000 mg per tablet). Because authoritative dosing guidance for supplementation is lacking, talk to a doctor or pharmacist before taking L-Lysine, especially if you are pregnant, nursing, have kidney problems, or take other medicines.
Safety
Lysine obtained in normal amounts from food is a routine part of the diet and not a distinct safety concern. The long-term safety of high-dose lysine supplements is not characterized by the government source reviewed, so anyone with kidney disease or other chronic conditions should consult a clinician before use, and supplements should be kept away from children unless advised by a healthcare provider.
Side effects
The authoritative US government source reviewed does not provide side-effect data for L-Lysine supplements, so a reliable safety profile cannot be given here. If you take L-Lysine and have an unexpected reaction, stop use and seek medical advice. Discuss any planned supplement use with a healthcare professional.
Interactions & cautions
The government source reviewed does not document specific drug interactions for L-Lysine. Because interactions cannot be ruled out from this source, tell your doctor or pharmacist about any prescription drugs, other supplements, or health conditions before starting L-Lysine.
This statement has not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. Summarized from public health authorities; general reference, not medical advice. Talk to a licensed healthcare professional before starting any supplement.