Driving under the influence is often called “drunk driving.” But it’s also illegal in every state to drive while under the influence of drugs. The DUI laws in all states prohibit driving while actually impaired by drugs. And some states also make it “per se” illegal to drive with a certain concentration of select drugs in your system.
Legal and Illegal Drugs
Generally, drug DUI laws apply to illegal and legal drugs alike.
The DUI laws in some states provide an exhaustive list of controlled substances and other intoxicants that can lead to a conviction. Other states have DUI laws that are more general and just say it’s illegal to drive under the influences of any “intoxicating substance” (or some similar term).
Per se DUI laws typically specify illegal concentrations of one or more common drugs, like methamphetamine, marijuana, and cocaine. For example, a number of states have per se laws making it illegal to drive with five or more nanograms of THC (the main psychoactive component in marijuana) per milliliter of blood in your body.
There are also states that take the per se concept a step further and make it illegal to operate a vehicle with any amount of a controlled substance in your system.
Prescription Drug Defense
A few states have a prescription medication defense. With this defense, a defendant can beat a DUI charge by showing that he or she was under the influence of a prescription drug taken as prescribed by a doctor. However, a warning on a prescription label against driving while on the medication may prohibit a defendant from using the defense.