L-Cysteine, available as L-Cysteine HCl (hydrochloride) or L-Cysteine base, is a semi-essential amino acid crucial for protein structure, antioxidant function, and overall physiological balance within the human body. As a precursor to glutathione, L-cysteine plays a vital role in supporting cellular defense against oxidative stress, detoxification processes, and tissue repair. Its molecular structure and involvement in various metabolic pathways underscore its significance in promoting diverse physiological functions.