Driving under the influence of marijuana is a serious criminal offense everywhere in the United States. Each state, city, and county enforces laws prohibiting people who have recently consumed cannabis from operating motor vehicles.

But the specific rules behind marijuana DUI law vary from place to place. Some are more stringent than others, but every state treats driving under the influence of marijuana as a misdemeanor or felony with the potential for jail time.

A marijuana DUI charge applies to any motorist who drives while impaired by cannabis (or cannabis combined with another intoxicant). But there is no common definition of “impairment,” so different states apply different standards.

How DUI laws apply to marijuana

While all 50 states have established a blood-alcohol level of 0.08 percent or higher – the ‘per se’ measurement used to prove impairment – as triggering a DUI charge, no such single standard is in place when it comes to marijuana DUIs. Instead, there are four different standards applied by states when determining a marijuana DUI charge.

Impairment DUI

Most states require prosecutors prove a driver was actually impaired while driving under the influence of marijuana. Prosecutors may seek to do this by establishing erratic driving, slurred speech, or even the smell of cannabis. This is in contrast to states with per se laws, where the mere presence of THC is enough to allow charges.

Even in “actual impairment” states, however, the motorist need not break other traffic laws or drive unsafely to face prosecution. For example, a driver involved in a no-fault collision may be arrested and charged with marijuana DUI if police find evidence at the crash scene of recent cannabis use.

Per Se Marijuana DUI

In six states, blood tests must show a minimal THC concentration before per se marijuana DUI charges can be filed. The blood test is conducted once a driver is arrested to determine the presence of THC metabolites. If found in sufficient concentration, the motorist can be charged. This approach, similar to the 0.08 percent cutoff for drunk drivers, varies substantially between jurisdictions. For instance, Ohio and Oklahoma set a THC blood limit of 2ng/ml while in Montana and Illinois a marijuana DUI charge is triggered at 5ng/ml.

Zero Tolerance DUI

In zero-tolerance states, of which there are eleven, the discovery of any amount of THC in a motorist’s bloodstream is per se grounds for a marijuana DUI charge. This includes inactive THC metabolites that can be detected hours, days, or even weeks after use. In other words, drivers who are not currently high can nonetheless be jailed in these places over the possession of lingering, non-intoxicating THC in their blood.

Permissible Inference Law

This marijuana DUI law only applies in Colorado, but is a variation on the per se standard. It’s triggered if THC is found in the driver’s blood at 5ng/ml or higher. If that’s the case, then it’s permissible to presume the driver was driving under the influence of THC.

Marijuana DUI laws by State

The diagram below provides a breakdown of the DUI laws that apply in different states.

State Marijuana Impaired Driving Laws

What constitutes “driving?”

For purposes of marijuana DUI charges, a motorist accused of driving under the influence of cannabis must have been “in actual physical control” of the vehicle. But this definition is much more inclusive than it may seem at first glance.

A driver need not be “driving” or “operating” a vehicle in the technical sense: Being “in actual physical control” includes being in control of a parked car. Judges consider several factors in determining whether a parked motorist was driving under the influence of marijuana:

  • Were the keys in the ignition? Did the driver even have access to them?
  • Was the engine running?
  • Was the car moving?
  • Was the vehicle operable?
  • Was the driver awake or “sleeping it off”?
  • Was there gas in the tank?
  • Was the driver sitting in the driver’s seat, the passenger’s seat, or the back seat?

A drunk or high motorist stranded away from home should take precautions before sleeping off the intoxication in a parked car. Avoid sleeping in either of the front seats, but especially the driver’s seat. Unless power is required for heat, leave the engine off and keys away from the ignition. Do not park and sleep along highways or in any other place that might suggest you parked after driving under the influence of marijuana.

Marijuana DUI penalties

Most motorists convicted of marijuana DUI face at least a criminal fine and suspended license, as well as jail time in many cases. DUIs are typically misdemeanors, but if a case rises to the level of a felony, a prison sentence is possible. Probation or house arrest is an alternative to incarceration frequently used in DUI cases.

It is also common for courts to suspend driving privileges for a period of months or years. In rare cases, usually involving repeat DUIs, judges may permanently revoke drivers’ licenses. Other potential penalties include:

  • House arrest
  • Community service
  • Participation in victim-impact programs
  • Forfeiture or impoundment of the vehicle
  • Mandatory substance-abuse treatment

Punishments usually vary based on the number and severity of offenses: First-time offenders typically face lighter penalties than those who have been convicted before. Aggravating factors may also increase sentences, such as:

  • The presence of a minor in the car
  • An underage driver
  • A DUI on a suspended license
  • A DUI while driving a school bus
  • Traffic collisions, property damage, physical injury, or death
  • Extremely high blood-THC levels

Sentencing range

Many states set maximum penalties for driving under the influence of marijuana, but relatively few apply mandatory minimum sentences on a first offense. Subsequent offenses, however, often do carry minimums. Otherwise, judges are generally free to hand down criminal sentences as they see fit.

It is not uncommon for first-time defendants in minor marijuana DUI cases to receive little or no jail time. But repeat offenders should expect at least a few days in jail, with increasing terms of incarceration for each conviction.

The rules for medical marijuana patients

Medical marijuana is legal in the vast majority of U.S. states, but driving under the influence of marijuana remains illegal in all of them. That means those who use cannabis medicinally throughout the day risk arrest whenever they get behind the wheel.

Patients are most at risk in states with zero tolerance or per se marijuana DUI laws, since these states penalize a motorist for the presence of THC metabolites, even when he or she was not high. The key for all medical cannabis patients is know your state’s specific DUI laws, never drive when impaired by marijuana, be aware of all local traffic laws, and carry patient identification at all times.