The effects of specific drugs on driving skills differ depending on how they act in the brain. For example, marijuana can slow reaction time, impair judgment of time and distance, and decrease coordination. Drivers who have used cocaine or methamphetamine can be aggressive and reckless when driving. Certain kinds of prescription medicines—including benzodiazepines and opioids—can cause drowsiness, dizziness, and impair cognitive functioning (thinking and judgment). All of these effects can increase the chances of vehicle accidents.

Research studies have shown negative effects of marijuana on drivers, including an increase in lane weaving, poor reaction time, and altered attention to the road. Use of alcohol with marijuana makes drivers more impaired, causing even more lane weaving. Some studies report that opioids can cause drowsiness and impair thinking and judgment. Other studies have found that being under the influence opioids while driving can double your risk of having a crash.

For these reasons, many states have laws making it a criminal offense to operate a vehicle under the influence of or while impaired or intoxicated by legal or illegal prescription or recreational drugs, for example—known as drugged driving or driving under the influence of drugs (DUID). And a driver’s use of a prescription medication is not a defense to operating a vehicle while impaired or intoxicated by the medication.

In many states the DUI/DWI statutes are broad enough to prosecute a driver who is under the influence of or impaired or intoxicated by prescription or recreational drugs—as well as alcohol or any other substance, including an inhalant with a vapor-releasing substance. And at least 15 states have per se (pronounced purr-say) drugged driving laws that make it a criminal offense to drive with any detectable amount of certain drugs in your system, or with a minimum prohibited amount of certain drugs, as provided in the state’s statutes. These states include Arizona, Delaware, Georgia, Illinois, Indiana, Iowa, Michigan, Minnesota, Nevada, Ohio, Pennsylvania, Rhode Island, Utah, Virginia, and Wisconsin.

Drugged driving laws are generally located in a state’s statutes—often in the penal code or criminal code.

In Colorado, driving under the influence of drugs (DUID) is a serious criminal offense. This includes impairment from the use of marijuana, prescription drugs such as benzodiazepines and opioids, and illegal substances like cocaine and methamphetamine. These substances can impair driving skills by affecting reaction time, judgment, coordination, and cognitive functions, increasing the risk of accidents. Colorado law prohibits operating a motor vehicle while impaired by any drug, whether legal or illegal, to the degree that the driver is unable to safely drive. This is similar to driving under the influence of alcohol (DUI). The use of prescription medication is not a valid defense against a DUID charge if the medication impairs the driver's ability to operate a vehicle safely. Colorado's approach to DUID does not rely on a per se standard based on the detectable amount of drugs in the system, unlike some other states that have such laws. Instead, impairment is typically assessed by the driver's behavior, physical signs, and performance on field sobriety tests, possibly supplemented by chemical testing for the presence of drugs.