Painkilling drug molecule. Computer model of a molecule of the painkilling prescription drug oxycodone hydrochloride (C18.H21.N.O4, tradename OxyContin). The atoms (spheres) are colour-coded: carbon (orange), hydrogen (white), oxygen (pink) and nitrogen (blue). A chloride ion (green, top left) forms a neutral salt with the nitrogen ion. OxyContin is a powerful drug that is used to treat chronic pain. It stimulates the same receptors in the brain that respond to drugs like opium and heroin, and like them is very addictive if misused. Because of this, OxyContin is classed as a controlled substance. OxyContin was first manufactured by the Purdue Pharma company.