Lysine

Lysine is an alpha-amino acid with the formula C6H14N2O2 and a basic, positively charged side chain. The L-enantiomer is the form built into proteins, where it is specified by the genetic codons AAA and AAG. It is classified as an essential amino acid because humans lack the pathway to synthesize it and therefore depend entirely on dietary intake. Lysine was first isolated by Edmund Drechsel in 1889 from the milk protein casein, its name deriving from the Greek word lysis; its structure was confirmed by synthesis in the early 1900s.

Beyond serving as a protein building block, lysine has several specific biological roles. Its side chains are modified to hydroxylysine and then cross-linked by the enzyme lysyl oxidase to give collagen and elastin their tensile strength, and lysine is a metabolic precursor for carnitine, a molecule that helps shuttle fatty acids into mitochondria for energy. Lysine residues in proteins are also common sites for regulatory chemical modifications such as acetylation and methylation.

In the diet, lysine is abundant in animal foods such as meat, fish, eggs, and dairy, and in legumes including soybeans, beans, and peas. It is the limiting amino acid in cereal grains, so diets built heavily around wheat, rice, or maize can fall short unless balanced with legumes, a pairing reflected in many traditional cuisines.

Commercially, lysine is produced on a very large scale by bacterial fermentation, chiefly using Corynebacterium glutamicum, and most of it is used to fortify livestock feed. As a human supplement, L-lysine is best known for a claimed benefit against cold sores, based on the idea that lysine counteracts arginine, an amino acid the herpes simplex virus uses to replicate. The clinical evidence for this is weak: controlled trials failed to show a clear benefit for recurrent herpes labialis ^[1][2], and a Cochrane systematic review found no evidence that lysine prevents cold sores ^[3]. Lysine is otherwise recognized as a normal dietary nutrient and is sold as L-lysine hydrochloride.

Lysine is generally very safe at typical doses; high doses can cause GI upset like cramps or diarrhea. Very high long-term intake is not well studied and could theoretically stress kidneys in people with existing kidney disease. It is otherwise low risk.

Lysine has a thin interaction profile, and saying so plainly is more useful than padding it out. Note also that ibuprofen lysine, a neonatal injectable, is a different substance; its interaction profile is ibuprofen's and does not transfer to lysine as a supplement.

The one interaction with a clear mechanism is with arginine. The two share the cationic amino acid transport system in the gut and at the renal tubule, so each competitively reduces uptake of the other; taken together in quantity they blunt one another. That matters mostly when arginine is being taken for a specific purpose of its own.

Lysine also increases intestinal calcium absorption and reduces urinary calcium loss, so in theory it adds to high-dose calcium and vitamin D. Reports of clinical hypercalcemia from that combination are absent. A suggested potentiation of aminoglycoside nephrotoxicity is likewise theoretical, resting on shared renal handling rather than on any case series.

Checking a whole stack? Run it through interactions + stacks.