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 New Jersey, driving under the influence of drugs (DUID), including legal prescription medications, illegal drugs, and marijuana, is a serious criminal offense. The state's laws recognize that drugs can impair driving abilities in various ways, such as reducing reaction time, impairing judgment, and decreasing coordination. New Jersey law prohibits operating a motor vehicle under the influence of any substance that impairs one's ability to drive safely. This includes not only illegal substances but also prescription and over-the-counter medications if they affect driving skills. The use of a prescription medication is not a valid defense against a charge of impaired driving. New Jersey does not have a per se drugged driving law that makes it an offense to drive with any detectable amount of certain drugs in one's system. Instead, impairment must be demonstrated. Penalties for DUID in New Jersey can include fines, license suspension, and even imprisonment. The state takes a strong stance against drugged driving to ensure the safety of all road users.