The problem: Impaired drivers can cause car accidents and people getting hurt. If a driver is impaired and if that impairment was caused by marijuana, that may be a DUI marijuana offense. And a conviction can result in all the DUI consequences, including driver’s license revocation.
Impaired driving, and DUI marijuana
But when is a driver impaired?
Impairment means that our performance is less than normal to the point of being unsafe. It could be less than normal for each one of us as an individual. Or, we could mean less than normal for the law’s mythical “reasonable person.”
If we’re talking about impaired driving, then the impairment must connect with driving somehow.
So, before we get to DUI marijuana, we have the threshold question: Is the person’s driving impaired?
Bad driving conduct
How can we tell if someone’s driving is impaired? Well, is the person driving poorly? Is it a “bad driving” case?
If a driver gets into a car accident, most wonder, was that driver at fault? If not, a car accident does not show bad driving. But it raises the question.
Or, a police officer may observe a driver driving badly. Swerving across three lanes of traffic might mean bad driving. Or, in isolation, the driver might have swerved to avoid hitting a deer. Good driving.
Police officers attempt to observe and document more than one instance of bad driving, to help prove possible impairment. This is the case in a DUI marijuana case as well.
Driver appears impaired
In some DUI cases, the police officer does not observe any driving. For example, a person found near a car with a flat tire may arouse police suspicion.
Whether or not the police officer observes driving, they will try to get evidence to show driver impairment. If they find evidence of recent marijuana use, police may investigate for DUI marijuana.
“Field Sobriety Tests” or field exercises
Police officers at a DUI stop ask the driver to perform “Field Sobriety Tests” (FSTs)
The National Highway Traffic and Safety Administration (NHTSA) standardized them as a screening test, but only for alcohol-impairment.
NHTSA’s three Standardized FSTs are the nine-step-walk-and-turn, the one-leg-stand and the Horizontal Gaze Nystagmus (HGN) test.
Police sometimes “request” additional FSTs looking for evidence of DUI marijuana. They may attempt to get the driver to cooperate with these at the police station. And they may call in another officer to do their “Drug Recognition Evaluation” (DRE). But no driver can be required to submit to these unfair “tests.” The driver can refuse them without fear of penalty.
Police observations of driver
In addition, police will selectively document those observations of the driver that support a theory of intoxication. But they ignore observations supporting a theory of sobriety. Just about every DUI police report notes:
- bloodshot, watery eyes
- odor of (alcohol) (marijuana)
Other common boilerplate notations include:
- fumbled for license and insurance card
- appeared nervous or tired
- used door for balance exiting vehicle
- used side of vehicle for balance
Preliminary Breath Test (PBT)
Most DUIs involve the odor of alcohol. The odor of alcohol alone is not enough, without other observations consistent with impairment. If so, police officers often ask the driver to blow into a Preliminary Breath Test. The PBT is a small, portable breath-alcohol machine. Refusing can give the police arrest probable cause. Blowing a 0.08 or more reading is also arrest probable cause.
In a traffic stop leading to a DUI marijuana investigation, police might also request the driver blow into a PBT. They will if the driver has an odor of alcohol.
Marijuana DUI specific police procedures
For DUI marijuana investigations, the usual DUI investigation is a bit different. Almost always, it begins with the police claim of an odor of marijuana. Then, the police ask questions about marijuana. Then, they search the driver and the car if they can.
See: How to Avoid a Marijuana Arrest in a Car in Minnesota.
If police find marijuana, they may charge marijuana in a motor vehicle.
Or, if they find wax, concentrates, or THC edibles, they may charge a felony or gross misdemeanor possession, depending upon quantity.
After that, the FSTs, DRE exercises (or field exercises) become more important. Some are the same as for alcohol. But some FSTs and DRE exercises relate specifically to drugs other than alcohol, including marijuana.
Know your rights: Never agree to do FSTs
Police cannot force anyone to do FSTs or DRE exercises. You can simply decline to do them. You should not make any excuses, either.
Just tell the police officer that you won’t do any field exercises or Field Sobriety Tests (FSTs), at all. You don’t need a reason or justification. You don’t have to do them. They can only hurt you.
NHTSA does not claim any FSTs or DRE exercises are scientifically valid for marijuana. The police officer is not a scientist or a medical doctor. It’s not a fair “test.” Police will note every imperfection to support the one conclusion. “Fail.” And they’ll ignore evidence, and the science, to the contrary. Don’t take that bait.
If you already did. Your DUI marijuana attorney can take steps to neutralize them.
Post-arrest: DRE
After an arrest at the roadside, the police officer takes the driver to either a hospital or a police station. In order to support a DUI marijuana charge, they think they need a urine or blood test. In reality, they need a blood test (or a refusal).
Urine or blood test
To get a urine or blood test, police need a search warrant signed by a judge. Ask to call an attorney prior to giving any sample for testing.
The marijuana DUI attorney on the phone can advise you about whether to submit a sample for testing; and about your right to an additional, independent test after theirs.
If you refuse a blood draw, police must offer the choice of a urine sample before labeling you a refusal. And, they must offer a blood test if you refuse urine, before charging you with chemical test refusal.
Chemical test results – DUI marijuana cases
Police must send the blood or urine test to a lab for analysis. That will take time. Without the lab results, there is no evidence of marijuana or THC in the body. So, charges should wait for the lab results, if any.
Lab reports for THC and metabolites
In a suspected DUI marijuana case, the lab will test for many prescription and other drugs, including THC. In addition to THC, the lab report will show results for THC-metabolites.
What are metabolites? When the body’s metabolism breaks down a chemical or drug into another chemical, it’s a metabolite.
Alcohol metabolites: For example, enzymes in the human body metabolize alcohol first into acetaldehyde, a toxic substance. Then, in a second step, our bodies metabolize acetaldehyde down to another, byproduct called acetate. Our bodies then break down Acetate into water and carbon dioxide for elimination.
Key take away: Metabolites of alcohol are not alcohol.
Marijuana metabolites: The marijuana plant component that causes impairment is THC. So, the lab tests the blood for THC (Δ9-tetrahydrocannabinol).
In addition, the lab tests for two metabolites of THC, hydroxy THC (11-OH-THC) and carboxy THC (THC-COOH). (In recent years the Minnesota BCA has added related cannabinoids and metabolites, such as Delta-8 THC to their lab panel. But these are of too little importance to discuss further here.)
Remember, a metabolite of THC is not-THC. Rather, a THC metabolite is another chemical. The body makes it as a byproduct of breaking down THC into other, different chemicals. And these THC-metabolites do not prove impairment.
Ignorance about metabolites and their meaning
Ignorance about the science of THC, metabolites and their effects leads to false charges of DUI marijuana. But Attorney Thomas Gallagher has helped clients get these cases dismissed.
The common confusion about this may stem from the use of “THC” in THC metabolites, hydroxy THC, and carboxy THC. So, remember:
- THC is the psychoactive ingredient in marijuana, can cause impairment
- THC metabolites are not THC, do not indicate current impairment
A lab test report includes levels for:
- THC
- Hydroxy THC, and
- Carboxy THC
- Other
So, then why test for metabolites? Because you can? It’s difficult to discern any relevance of Carboxy THC for purposes of DUI enforcement, other than potential to confuse some. After all, Carboxy THC:
- has zero psychoactive effect; none
- blood level rises after THC blood level declines
- can remain detectable for over 30 days – so has zero value as proof of recent use
- can prove past use, but not recent use or impairment
Hydroxy THC is detectable in blood up to 24 hours after last use, depending on method of ingestion. As a result, we can use Hydroxy THC in combination with blood THC level to approximate a rough time range of last use.
No Retrograde Extrapolation for DUI Marijuana
The theory of retrograde extrapolation (sometimes, “back-extrapolation“), attempts to work backwards from the time of a known test level to determine a driver’s blood alcohol level at the time of arrest or of an accident. It requires a reliable alcohol test with a level of alcohol concentration, as measured at the time of the sample. Then with multiple other known facts, such as the test subjects gender, weight, etc., it attempts to “extrapolate” what the subjects alcohol concentration level would have been at some point in the past.
But the consensus among scientists in the field is that retrograde extrapolation is not scientifically valid for THC and marijuana. As a result, retrograde extrapolation should not be used for THC in court.
The human body’s elimination of THC is non-linear. So back-extrapolation of concentrations to an earlier time is not possible. “Back-extrapolation is not an option due to the complex pharmacokinetic profile of THC.“ (Willie et al, 2010. Conventional and alternative matrices for driving under the influence of cannabis, Bioanalysis). The body may have residual metabolite and THC levels for long periods of time following cannabis exposure, without any psychoactive effects. And testing cannot differentiate past exposure from more recent exposure. Reverse-extrapolation is not possible.
Practical Implications: No Reverse Extrapolation Evidence
The most common use of reverse extrapolation evidence in DUI Alcohol cases is in injury crash investigations. But police can also attempt it where they miss the two-hour period from the time of driving.
But for DUI Marijuana cases, the first issue is that blood-THC levels do not correlate with impairment, unlike alcohol. Then, even if they did, the body’s elimination of THC is non-linear. This makes retrograde extrapolation of blood THC levels to some time prior to the time of testing, impossible.
Next, this helps us understand why urine tests in DUI Marijuana cases are useless. Urine tests show metabolites. Urine test lab reports may not list Delta-9 THC, because if they did, they might show trace levels (extremely low). Remember, the issue in a DUI cases is “was the driver’s driving impaired by a specific drug such as alcohol or THC.”
Since a Urine Test will not indicate THC levels, the psychoactive ingredient in marijuana; it will not be good evidence of impairment caused by THC. Contrast that with a Blood Test. A Blood Test can show a reliable THC blood level, at a specific point in time. (Though, again, THC levels do not correlate with impairment. Other evidence might indicate impairment.)
A purpose of most marijuana testing, for example of probationers, has been to detect any past use. And some testing parameters look for recent use. But for purpose of DUI, the testing purpose is detecting current presence and level of the potentially impairing drug, THC, not inert metabolite.
Minnesota Law Currently Requires Urine if Blood Refused
Minnesota law currently requires police officers requesting a blood test in a DUI Marijuana case, to offer a Urine Test if the arrested person refuses a blood test. Do you see the practical implication of the limitations of urine testing? The prosecution could be stronger with a blood test, rather than a urine test. A future legislature might amend this. Ideally, they would simply eliminate urine testing for DUI enforcement in Minnesota, as almost all other states have already done.
If the driver refuses both blood and urine following a lawful request by a police officer, the driver may face criminal charges for DUI – refusal to provide a sample for chemical testing.
D-9-THC in blood does not prove impairment, regardless of level
“One of the program’s objectives was to determine whether it is possible to predict driving impairment by plasma concentrations of THC and/or its metabolite, THC-COOH, in single samples. The answer is very clear: it is not.
US National Highway Traffic Safety Administration, Marijuana and Actual Driving Performance, 1993
Plasma of drivers showing substantial impairment in these studies contained both high and low THC concentrations; and, drivers with high plasma concentrations showed substantial, but also no impairment, and even some improvement.”
NHTSA and the scientific studies say, there is no correlation between blood plasma THC levels and impaired driving.
That seems counterintuitive to most people. Most people have personal experience with alcohol. Blood alcohol levels do roughly correlate with impairment. But alcohol and THC are quite different, in this way.
“THC’s effects differ qualitatively from many other drugs, especially alcohol. For example, subjects drive faster after drinking alcohol and slower after smoking marijuana. … Very importantly, our city driving studied showed that drivers who drank alcohol over-estimated their performance quality whereas those who smoked marijuana under-estimated it. …
“[S]ubjects in the marijuana group were not only aware of their intoxicated condition, but were … attempting to compensate for it. These … findings … support … the common belief that drivers become overconfident after drinking alcohol and … that they become more cautious and self-critical after consuming low doses of THC, as smoked marijuana.”
“… comparable to risks such as talking on a hands-free cellphone …”
US National Highway Traffic Safety Administration, Marijuana and Actual Driving Performance, 1993
Minnesota Statutes and DUI marijuana
Minnesota Statutes §169A.20 is the general DUI statute. Here are the most relevant parts:
“Subdivision 1. Driving while impaired crime; motor vehicle.
It is a crime for any person to drive, operate, or be in physical control of any motor vehicle, as defined in section 169A.03, subdivision 15, except for motorboats in operation and off-road recreational vehicles, within this state or on any boundary water of this state when:
(1) the person is under the influence of alcohol;
(2) the person is under the influence of a controlled substance;
(3) the person is under the influence of an intoxicating substance and the person knows or has reason to know that the substance has the capacity to cause impairment;
(4) the person is under the influence of a combination of any two or more of the elements named in clauses (1) to (3); …
or
(7) 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.
Subd. 2. Refusal to submit to chemical test crime.
It is a crime for any person to refuse to submit to a chemical test:
(1) of the person’s breath under section 169A.51 (chemical tests for intoxication), or 169A.52 (test refusal or failure; revocation of license); or
(2) of the person’s blood or urine as required by a search warrant under sections 171.177 and 626.04 to 626.18.
Penalties and consequences for DUI marijuana
The penalties and consequences of a marijuana DUI are similar to any Minnesota DUI case.
For example, a fourth within 10 years is Felony DWI with a presumptive prison sentence.
There is one important difference, however.
With an alcohol DUI, the state revokes your driver’s license immediately after a chemical test over the per se 0.08 limit. And it revokes your license upon a refusal to test. There is no per se limit for THC, however, and for good reason.
The science, and NHTSA agree, there is no specific THC level that correlates with impairment. In fact, some drivers drive better with THC than other drivers with no THC. As a result, a per se limit for THC would make zero sense.
So, the state will not revoke your driver’s license before conviction for DUI marijuana, unless you refuse chemical testing. Your attorney can help you with any questions about this.
For more on the relative risks of DUI-marijuana, see our in depth article: The Myth of Marijuana DUI vs. Science.
Defenses in DUI marijuana cases
The hundreds of defenses available in any DWI case are available in a marijuana DUI. But there are also some defenses specific to DUI marijuana cases. These include evidence about THC and its metabolites, and the effect of THC on driving.
Your DUI Marijuana Attorney
Should you have a DUI Marijuana Attorney with specific training and experience? Attorney Thomas Gallagher has that. In fact, Thomas Gallagher teaches DUI Marijuana law in Continuing Legal Education (CLE) courses to prosecutors, defense attorneys and judges.
Thomas Gallagher is an expert DUI Marijuana defense attorney.
Would you like him to represent you? Or, do you have a question? You can call Attorney Thomas Gallagher for caring, expert assistance at 612 333-1500.
Other articles of interest
Marijuana Laws in Minnesota
Driving Offenses in Minnesota
How to Avoid a Marijuana Arrest in a Car: Nine Tips