Methionine is an essential amino acid that is not synthesized by the body, and therefore must be obtained from food. It is one of the sulfur-containing amino acids and is important in many body functions. Through its supply of sulfur, it improves the tone and pliability of the skin, conditions the hair and strengthens nails. The sulfur also protect the cells from free radical damage and may slow down the aging process in the cells, and is involved with the production of protein. Methionine is essential for the absorption and transportation and bioavailability of selenium and zinc in the body. It also acts as a lipotropic agent to help prevent excess fat buildup in the liver, and is an excellent chelator of heavy metals, such as lead, cadmium and mercury, binding them and aiding in their excretion from the body.

Methionine can help fatigue and may be useful in some cases of allergy because it reduces histamine release. It has also been used in the treatment of rheumatic fever and toxemia resulting from pregnancy. Recent studies show methionine deficiencies may be associated with the development of age related cataracts, and supplements may delay their development. In Parkinson's disease patients taking L-Dopa, it was found that additional supplements with L-Methionine may further decrease the tremors and rigidity that limit normal activities.

Methionine is available from natural and synthetic sources.