Driving under the influence of drugs (DUID) is the operation of a motor vehicle while under the influence of or impaired by any type of drug, legal or illegal. This includes marijuana, prescription drugs, and some over-the-counter medications.

While research estimating the crash risk of driving under the influence of drugs is ongoing, many experimental studies have shown that drugs impair attention, alertness, reaction time, lane tracking, coordination, and perception of time and distance.  Even small amounts of some drugs can have a serious effect on driving ability.