Morphine. Computer model of a molecule of morphine (C17.H19.N.O3). The atoms (tubes) of this drug are colour-coded: carbon (purple), oxygen (red), hydrogen (grey) and nitrogen (yellow). This drug is a powerful narcotic (inducing a stupor) and analgesic (relieving pain). It is administered by mouth or by injection in order to relieve severe or persistent pain. Side-effects include nausea, loss of appetite, constipation, confusion and also feelings of euphoria. Patients can rapidly develop tolerance, requiring ever-higher doses to relieve their pain. Addiction is also possible, and doses that are too high (overdoses) can kill.