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 Louisiana (LA), driving under the influence of drugs (DUID) is illegal and considered a serious offense. This includes the influence of marijuana, which can impair reaction time, judgment, and coordination, as well as cocaine, methamphetamine, benzodiazepines, opioids, and other prescription or recreational drugs that can cause drowsiness, dizziness, and impaired cognitive functioning. Louisiana's laws prohibit operating a vehicle while impaired or intoxicated by any substance, including legal or illegal drugs. The use of prescription medication is not a valid defense against a charge of impaired driving. While Louisiana does not have a per se drugged driving law that makes it a criminal offense to drive with any detectable amount of certain drugs in one's system, the state's DUI statutes are broad enough to cover driving under the influence of drugs. The relevant laws are typically found in the state's penal or criminal code, and they aim to reduce the risk of vehicle accidents caused by impaired driving.