L-Cystine dihydrochloride is the hydrochloride salt form of L-cystine, a dimeric amino acid formed by the oxidation of two cysteine molecules linked via a disulfide bond. It is a white to off-white crystalline powder that is soluble in water. This compound serves as a key source of the sulfur-containing amino acid cysteine in pharmaceutical and nutritional applications. It is widely used as a raw material in the synthesis of various drugs and as a nutritional supplement in parenteral and enteral nutrition formulations to support protein synthesis and metabolic functions. In the pharmaceutical industry, it also finds application as a stabilizer or excipient in certain formulations. L-Cystine and its salts are essential for maintaining cellular antioxidant systems (e.g., glutathione synthesis) and are crucial for the structure of many proteins and peptides. Its hydrochloride salt form offers improved solubility for specific formulation needs.