The limiting substrate for GSH synthesis is the amino acid cysteine.Oral cysteine is rapidly catabolized in the GI-tract, carries a toxic potential, and is not recommended.

• 谷胱甘肽的关键基质是半胱胺酸，口服半胱氨酸在肠胃道内会被快速的代谢掉具有相当的毒性，因此不适于服用。