L-Histidine Hydrochloride is used in the treatment of nutritional deficiencies.

L-Histidine hydrochloride is the obligate precursor of histamine, which is produced via the decarboxylation of the amino acid. In experimental animals, tissue histamine levels increase as the amount of dietary L-histidine increases. It is likely that this would be the case in humans as well. Histamine is known to possess immunomodulatory and antioxidant activity. Suppressor T cells have H2 receptors, and histamine activates them. Promotion of suppressor T cell activity could be beneficial in rheumatoid arthritis.