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.

Thiamphenicol is a broad-spectrum antibiotic, which is active against gram-positive and gram-negative organisms. The drug is marketed in Asia and Latin America for the treatment of various infections, including sexually transmitted diseases. As many phenicols, thiamphenicol inhibits the protein synthesis in bacterias by binding to 23S ribosomal subunit. In Europe and USA the drug is used in a veterinary practice.