Marijuana DUI - Actual Impairment Required

With 4/20 having come and gone recently, we thought it’d be an appropriate time to discuss the marijuana DUI laws in Minnesota. Certainly, with the likely legalization of marijuana in the not-too-distant future, marijuana DUI’s will become more commonplace. But that doesn’t mean they will be easy to prove. Because, as the current law stands, the mere presence of marijuana in the system does not result in a DUI. So let’s explore what the current laws (as of April 2021) require for a marijuana DUI.

Minnesota Driving Under the Influence of Controlled Substance Laws

Minnesota’s driving under the influence laws begin at Minn. Stat. 169A.20. Subdivision 1(7) states that it is a crime for any person to drive, operate, or be in control of a motor vehicle when the person’s body contains any amount of a controlled substance listed in Schedule I or II, or its metabolite, other than marijuana or tetrahydrocannabinols. There is a per se rule for being under the influence if you have any amount of schedule I or II drugs in your system, except for marijuana.

To prove a marijuana DUI, then, the State must prove actual impairment under Minn. Stat. 169A.20, subdivision 1(2), which makes it a crime to be “under the influence of a controlled substance.” THC is a schedule I controlled substance, permitting the State to try to prove a marijuana DUI if it can prove your impairment.

Proving a Marijuana DUI 

Proving a marijuana DUI is not an easy task and is different in meaningful ways to proving an alcohol DUI. To begin with, dosage levels, tolerance, and weight can play a part in whether a person experiences signs of impairment from inhaling or consuming marijuana. And, as of yet, there is scant evidence suggesting that a specific THC level in the body will result in impairment. This is in contrast to an alcohol DUI where someone testing above a .08 is deemed to be impaired under the law.

Recently, the National Institute of Justice and researchers from RTI International conducted a study on how marijuana affects a person’s performance on field sobriety tests. The study focused on different dosage levels as well as the method of administration, that being whether the marijuana is vaped or consumed orally. The study found that a person’s THC level is not a reliable indicator of marijuana impairment. While many of the study’s participants experienced a decrease in cognitive and psychomotor functioning at low THC levels, the researchers observed that standard field sobriety tests were not effective in detecting marijuana intoxication.

This is important because most cops are training in administering the standardized field sobriety tests that are designed to assess impairment caused by alcohol. There is a separate sequence of testing that is specifically designed to assess possible impairment caused by controlled substances. This is a DRE – drug recognition evaluation. And it requires additional training that not many cops have received. The result is that a DRE is not always done during a DUI of controlled substances, even though it’s nearly a must. 

And even if a DRE is performed, a recent court of appeals decision held that it is mindful to not give too much weight to a defendant’s performance on these field sobriety tests. That same court noticed that most cases where a driving while impaired conviction was upheld involved impaired driving conduct – for instance, erratic or aggressive driving, or an accident. But, when the driving while impaired conviction was based solely on impairment factors and not driving misconduct (i.e. the stop was for speeding), then it becomes a lot harder for the State to secure the conviction. One Minnesota Supreme Court case found the following facts to be insufficient to support an DUI conviction: bloodshot and watery eyes, smell of alcohol, difficulty in understanding the defendant, and the defendant became aggressive with the cops multiple times.  

Hiring a DUI Defense Attorney

As you can see, to prove a marijuana DUI, the State will most likely need a combination of facts to obtain a conviction. Those facts include both poor driving conduct and behavior consistent with impairment. This shows why it is so critical to get a Minnesota DUI attorney to fight on your behalf. With so much at stake – including the potential loss of license, plate impoundment, and a criminal record – having an experienced Minnesota DUI attorney is a must. 


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