WHAT IS L-CYSTEINE? L-Cysteine is an amino acid that is only included to a small degree in proteins (2%). Environmental factors can raise the need for L-Cysteine as part of your diet. OUR N-ACETYL L-CYSTEINE SUPPLEMENT This individual amino acid supplement provides pure N-Acetyl L-Cysteine in capsule form. N-Acetyl is a stable form of the amino acid L-Cysteine and is a precursor to glutathione.  WHY N-ACETYL L-CYSTEINE N-Acetyl is a stable form of the amino acid L-Cysteine and is a precursor to glutathione. EXCIPIENT FREE Our L-Cysteine supplement comes in the form of a vegetable cellulose capsule. This enables us to offer a supplement that does not require excipients, binders or unnatural fillers. A vegetable cellulose capsule is designed specifically to break down naturally within the acid of your stomach, ensuring that the nutrients are absorbed during digestion.