Cysteine – Uses, Benefits, Sources and Dosage Cysteine is an amino acid which can be synthesized in the body or it may be consumed through diet. It is a building block of proteins. It is an important amino acid formed in the body which is made from the methionine in the presence of vitamin B6. When it is taken in the form of supplement then it is formed in the form of N-Acetyl Cysteine (NAC). After entering into the body,