Illustration of the molecular structure of oxycodone (C18.H21.N.O4), a semi-synthetic opioid used to treat moderate to severe pain resulting from surgery, injury, or illness. It works by blocking pain signals from the central nervous system and the brain, to the rest of the body. It can be highly addictive and lead to dependency. Atoms are represented as spheres and are colour-coded: carbon (grey), hydrogen (white), nitrogen (blue) and oxygen (red).