Methionine is a substrate for the formation of other amino acids such as cysteine and taurine, versatile compounds such as SAM-e, and the important antioxidant glutathione.

Methionine is also an important part of angiogenesis, the growth of new blood vessels. Supplementation may benefit those suffering from copper poisoning.
Hair color; Loss of methionine has been linked to senile greying of hair. Its lack leads to a buildup of hydrogen peroxide in hair follicles, a reduction in tyrosinase effectiveness, and a gradual loss of hair color.

Methionine raises the intracellular concentration of GSH, thereby promoting antioxidant mediated cell defense and redox regulation. It also protects cells against dopamine-induced nigral cell loss by binding oxidative metabolites.
Methionine is an intermediate in the biosynthesis of cysteine, carnitine, taurine, lecithin, phosphatidylcholine, and other phospholipids. Improper conversion of methionine can lead to atherosclerosis due to the accumulation of homocysteine.
Methionine might also be essential to reversing damaging methylation of glucocorticoid receptors caused by repeated stress exposures, with implications for depression.