Encyclopedia · supplement
L-lysine
An essential amino acid once paired with iron for women with shedding, with no recent independent trial.
Supplement
Cost $
Safety: minor
What it is
Lysine is an essential amino acid, found in meat, fish, dairy and legumes.
How it works
It may help iron absorption and use, which is why one research group paired it with iron. The hair mechanism is unproven.
What the studies show
- A 2002 narrative review states that double-blind data confirmed an open study in which many women with increased shedding responded to lysine plus iron. It recommends a ferritin of around 70 micrograms/L as a target and warns that excessive supplements can themselves cause hair loss. We could not check the original trials, so the size of the effect is unknown. Rushton 2002
- We found no newer controlled trial of lysine for hair.
Side effects and safety
Well tolerated at food-level and modest supplement amounts; high doses may upset the stomach.
Bottom line
A protein-adequate diet covers lysine. Iron status matters more; see iron and ferritin. Lysine is not a proven standalone treatment. Discuss with a doctor.
Studies 1
Rushton DH et al. Nutritional factors and hair loss. 2002
Result: Recommends ferritin around 70 micrograms/L for increased shedding, reports lysine plus iron responses, and warns that excess supplements can cause hair loss.
Read the study ↗Related
- Iron and ferritinLow iron stores are common in people who shed hair, but no trial has shown that iron pills regrow hair, and nobody agrees on a hair-specific ferritin target.
- L-cysteineAn amino acid that makes up much of hair keratin, with no controlled hair trial on its own.
- Hair supplement blends (Nutrafol, Viviscal and similar)Branded multi-ingredient hair vitamins that beat placebo in small, mostly company-linked trials.
- Diet and hairCrash diets and rapid weight loss cause shedding, ordinary diets rarely do, and testing beats guessing before you buy supplements.