Cysteine (cysteine hydrochloride is a salt) is a thiol-containing amino acid that is oxidized to form cystine. Cysteine is synthesized from methionine via the trans-sulfuration pathway in the adult, but newborn infants lack the enzyme, cystathionase, necessary to effect this conversion. Therefore, cysteine is generally considered to be an essential amino acid in infants.

Thiamine, also known as vitamin B1, plays a key role in the human metabolism. It is present in many dietary sources such as meats, eggs, fish, beans and peas, nuts, and whole grains. Upon administration thiamine is converted by thiamine pyrophosphokinase-1 (TPK1) to the active form, thiamine pyrophosphate, which serves as a cofactor for enzymes involved in the TCA cycle and the non-oxidative part of the pentose phosphate pathway. The lack of thiamine may cause the thiamine deficiency. The classical syndrome caused primarily by thiamine deficiency in humans is beriberi, however, symptoms of thiamine deficiency also include congestive heart failure, metabolic acidosis, confusion, ataxia and seizures. Thiamine is a component of many vitamin complexes, which are approved for the treatmen and prevention of general vitamin deficiency, including the thiamine deficiency.