A Drug Recognition Expert (DRE) is a law enforcement officer who has completed special training to recognize the various signs of drug impairment. After an arresting officer has taken custody of an impaired driver, a DRE may conduct a 12-step examination of the driver to establish proof of intoxication. Some illicit drugs are more difficult to detect than others, but a DRE may know how to spot the physical and mental signs of impairment.