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L-cysteine is a sulfur-bearing amino acid that occurs naturally in protein foods. When used as a supplement, N-acetylcysteine (NAC) is the preferred form of l-cysteine because it is more stable and more easily absorbed. Sufficient amounts of l-cysteine are usually available through the diet in such high protein foods as cottage cheese, yogurt, various meats, granola and wheat germ.
L-cysteine is a precursor to the antioxidant glutathione, which is severely depleted by toxic burdens placed upon the liver by drugs, alcohol, pollution, smoke and industrial chemicals. In a clinical setting, the NAC form of l-cysteine is sometimes used to counteract overdoses of specific substances like acetaminophen.1 L-cysteine is also used by itself and in combination with other nutrients to support more robust hair growth; hair is about 8% cysteine by weight.2
Use as directed. L-cysteine is available in capsule, tablet and powder form.
Mild gastrointestinal discomfort or rash may occur in some. May cause headaches, especially in those taking nitrates for the treatment of angina. Children or pregnant/nursing women should not take l-cysteine or NAC except under the advice of a physician. l-cysteine or NAC supplements are not recommended for those prone to kidney stones.
1. Toxicology. 2008 Feb 3;244(1):25-34. Epub 2007 Nov 7.
2. J Invest Dermatol. 1993 Jul;101(1 Suppl):56S-59S.