What is it?Holland & Barrett N-Acetyl Cysteine NAC Capsules contain 600mg of N-Acetyl Cysteine per capsule. Cysteine is one of 20 amino acids that are the building block of proteins used throughout the body. Cysteine Is One Of 20 Amino Acids That Are the Building Block of Proteins Acetyl L-Cysteine for Stability and Increased Bioavailability Suitable For Vegetarians and Vegans What Are the Benefits of This Supplement?Protein forms the structure of all the body's cells and tissues, including muscle tissue, internal organs, tendons, hair, skin, and nails. Cysteine is a non-essential amino acid as it is one of 12 amino acids that can be produced naturally by the body. Acetyl L-Cysteine provides stability, increased bioavailability and is an altered form of the amino acid L-Cysteine.