Ketamine molecule. Computer model of a molecule of the recreational drug ketamine (C13.H16.Cl.N.O). The atoms (balls) are colour-coded: carbon (light blue), hydrogen (grey), chlorine (green), oxygen (red) and nitrogen (dark blue). Ketamine is a non- barbiturate, rapid-acting anaesthetic that is used in medicine. It is also abused as a recreational drug that can produce a wide range of effects from rapture to paranoia to boredom. Overdose can cause death, and long-term use can cause psychological problems including dependence on continued use of the drug. Its sale and use, except for medical purposes, is illegal in many countries.