Hydrocodone drug. Molecular model of the analgesic drug hydrocodone (C18H21NO3) emblazoned with the flag of the USA. Atoms (spheres) are colour-coded: carbon (white stars on blue background), hydrogen (red stripes on white background), nitrogen (blue, just visible at lower right) and oxygen (red, seen at upper left). Hydrocodone is an opiate analgesic (painkiller) that is usually combined with other drugs, such as aspirin or paracetamol.