Opiates are powerful drugs derived from the poppy plant that have been used for centuries to relieve pain. They include opium, heroin, morphine, and codeine. Even centuries after their discovery, opiates are still the most effective pain relievers available to physicians for treating pain. Although heroin has no medicinal use, other opiates, such as morphine and codeine, are used in the treatment of pain related to illnesses (for example, cancer) and medical and dental procedures. When used as directed by a physician, opiates are safe and generally do not produce addiction. But opiates also possess very strong reinforcing properties and can quickly trigger addiction when used improperly.