A DRE is a drug recognition examination. That is given by usually a police officer that has been trained and gone to more extensive training than your typical DUI investigations. The reason is because they are test designed for the recognition of drugs, prescription drugs. There are certain nystagmus, which means that they're checking your eyes in a different way. There's also different exercises or tests that they've set up to determine whether or not an individual's impaired under the influence of drugs.