Methadone is composed of covalent bonds between 21 moles of carbon, 27 moles of hydrogen, and one mole of nitrogen and oxygen. It is most often found to be combined with HCl to form methadone hydrochloride. By mass methadone is: 81.6% Carbon, 8.7% hydrogen, 5.2% oxygen, and 4.5% nitrogen. By number methadone is: 42% carbon, 54% hydrogen, 2% nitrogen, and 2% oxygen.
Methadone is soluble in water, isopropanol, and chloroform. It is insoluble in ether and glycerine. When methadone is administered some inactive ingredients are present. These ingredients are sodium chloride, sodium hydroxide, and/or hydrochloric acid, their purpose is to adjust the pH of the compound, which is between 4.5 and 6.5.