Medical Marijuana Users have a Limited DUI Defense; Not General Immunity from Prosecution

Arizona Supreme Court Ruling: AMMA Users have an Affirmative defense for DUI. They can show they did not have a high enough concentration of THC to cause impairment.

The Arizona Supreme Court provided a unanimous decision in a recent Marijuana DUI ruling.  The court took a closer look at how the AMMA impacts prosecution.

The Supreme Court ruled that Medical Marijuana card holders are not immune from prosecution under the state’s DUI law, which prohibits drivers from having in their blood marijuana or another chemical compound that causes impairment.

At the same time, the court also ruled cardholders, do in fact, have a limited affirmative defense under the AMMA. But it is a limited DUI Defense. The AMMA does not, and does not provide general immunity from prosecution.

If a qualified user is facing marijuana DUI charges, they can provide a evidence or testimony showing they didn’t have a high enough concentration of the active ingredient THC, in Marijuana, to cause driving impairment.

If they are successful in their challenge of impairment, they may avoid a conviction.


This article will cover the following topics:

  • Arizona Supreme Court Ruling on Marijuana DUI;
  • Impacts of Ruling on Arizona Drivers;
  • Affirmative Defenses in Arizona;
  • When the Safe Harbor defense for Medical Practitioner Prescribed Drugs applies;
  • 5 types of evidence that can be used to provide a showing of non-impairment;
  • How many puffs does it take to cause Driver Impairment? 
  • Criminal Defense for Marijuana DUI Charges Mesa AZ

   Arizona Supreme Court Case Overview

Petitioners made no effort to show that the marijuana was in an insufficient concentration to cause impairment.” –  Arizona Supreme Court 

The case involved two defendants, both charged with two counts of driving under the influence:  a violation of A.R.S. § 28-1381(A)(1) and a violation of A.R.S. § 28-1381(A)(3).

The former, (A)(1), prohibits someone from driving while under the influence of any drug if he or she is impaired to the slightest degree.

The latter, (A) (2), prohibits driving while there is any of certain enumerated drugs or their metabolites in the person’s body. Both defendants had taken blood tests that showed they had marijuana and its metabolites in their bodies.

One of the defendants wanted to present evidence of her medical marijuana card in another state, but the municipal court denied her motion. The other held an Arizona medical marijuana card, but the municipal court granted the state’s motion to preclude this evidence from being introduced.

The State dismissed the (A)(1) charge, for driver impairment.

But the defendants were convicted of the (A)(3) charge which states that a person is in violation of a violation of the DUI law if they are driving with any drug found in their system which falls within the state’s drug definitions A.R.S. 13-3401 that includes “Cannabis”. 

The defendants appealed to the Maricopa County Superior Court, which affirmed the convictions. They then appealed to the Arizona court of appeals, which ruled that there was no immunity for defendants holding marijuana cards when charged with (A)(3).

The defendants asked the Arizona Supreme Court to review the case.

The Court explained that with an (A)(3) charge, unlike an (A)(1) charge, the state isn’t required to prove actual impairment.

The defenses for these charges are also different.  With an (A)(1) charge where a person is in violation of the law if they are driving impaired due to drugs or alcohol.  With that, it is not a valid defense against impairment to challenge the violations on the ground that the user has a medical marijuana card.

With the (A)(3) charge involving driving under the influence of the state’s defined drugs, there is an Affirmative Defense available.  This defense makes it lawful to drive under the influence of the state’s defined drugs, if they the drugs are prescribed by a licensed doctor.

The Court explained that the Arizona Medical Marijuana Act (AMMA) immunizes registered qualifying patients for their medical use of marijuana, but the immunity is limited.

AMMA’s § 36-2802 provides immunity to qualified patients who use marijuana to the extent that a registered qualifying patient shall not be considered to be under the influence of marijuana solely because of the presence of metabolites or components of marijuana that appear in insufficient concentration to cause impairment.

The Court also held that possessing a registry card can create a rebuttable presumption that a particular person is using marijuana as permitted by AMMA, as long as he or she isn’t in possession of more than the permitted amount.   This means that the police, prosecution, and court will assume it is true, unless the facts are challenged and proven otherwise.

Generally a defendant may be convicted of an (A)(3) violation if the state is able to prove beyond a reasonable doubt that the driver had marijuana or an impairing metabolite in her body while driving a vehicle.

As a defense, the defendant may show by a preponderance of the evidence that use was authorized by AMMA, and that the amount of marijuana was not enough to cause impairment. Simply presenting a registry card is not enough to establish this defense.

The defendants argued that it was unfair to place the burden of proof on them because there is no threshold that is commonly accepted as

the point of impairment.  But the court stated that the risk of uncertainty should fall on patients who should know when they can drive, rather than on the public.

The Court noted that the defendants did not attempt to show that the active ingredients in marijuana, found in their systems, were in an insufficient concentration to cause driving impairment.

Further the Court ruled that possession of registry cards is generally admissible evidence. However, any error in that regard was harmless in light of the positive THC blood test evidence,  and the fact that no effort was made to challenge driving impairment .

The defendants’ convictions were affirmed.

Impact of Ruling on Arizona Drivers   

[A.R.S. § 36-2802 (D) & A.R.S. §13-205]

The ruling will have the following impacts on qualified medical marijuana users driving in Arizona:

  • If arrested, it may be necessary for the defendant to secure expert witness to testify on why they did not feel the defendant had enough THC in concentrations high enough to cause impairment.    This can be problematic since that amount is variable, and there is no statutory or numeric identifier of that amount, which continues to be in controversy in the courts, and the industry.
  • Arizona, unlike some other states who have passed Medical Marijuana laws, do not have a statutory amount allowable for users to have in their system while driving a vehicle. As a result, the risk of uncertainty shifts to the patient.  It is up to the driver/patient to recognize if they are impaired or the active ingredient in Marijuana, THC concentration is high enough to result in driving impairment.
  • According to the National Institute of Health the impairing effects of alcohol between individuals vary due to the marijuana THC concentrations, strains of marijuana, the user’s tolerance, smoking technique, driving strategies, and different absorptions levels. Due to the variances the impairing amount will vary by individual.

 Affirmative Defenses in Arizona  

     [A.R.S. 13-205]

An affirmative defense is one in which a defendant admits to committing an act, but  challenges charges based on the fact that elements of law exist to excuse them from criminal liability under their circumstances.

Generally, the prosecution has the burden of proving beyond a reasonable doubt that a person is guilty of a crime committed.

Proof “beyond a reasonable doubt is a higher standard that of “preponderance of the evidence” standard.

With that, Under A.R.S. 13-205, when an affirmative defense is use, the burden of proof shifts to the defendant to prove their innocence by a “preponderance of the evidence” standard.

An Affirmative defense differs from a Justification Defense.  In Justification defense such as self-defense the burden of proof shifts to the prosecution to prove beyond a reasonable doubt that the defendant is guilty.

            Defense for Medical Practitioner Prescribed Drugs Denied  

                                    [A.R.S. § 28-1381 (2) (D)]

In this case the defendants raised another Affirmative defense challenge, in what some refer to as the “Safe Harbor” Law for drivers under the influence of prescription drugs.

Under Arizona’s DUI law A.R.S. § 28-1381 (2) (D), drivers are allowed immunity from criminal liability if they are using a drug as prescribed by a licensed medical practitioner as defined by the State of Arizona.     

The court rejected that argument, on the grounds that medical marijuana used by qualifying patients do so pursuant to “written certifications” under the AMMA; and that they are not considered to be “prescribed” as defined by the  state laws.

Further, the Court ruled that this defense applies to drugs prescribed by a different class of licensed “medical providers” than those who may issue medical marijuana certifications. For example, the DUI law A.R.S. § 28-1381 defines “medical providers” as including licensed dentists, or medical doctors.

In contrast, the AMMA law 36-2801 “physician” is defined as including both licensed medical doctors and naturopathic and homeopathic physicians.

5  types of Evidence that can be used to Prove You were Not Driving Impaired

Here are at least 5 examples of evidence that may be admitted in defense that a person was not driving impaired:

  • Qualified expert witness testimony;
  • Eye witness testimony;
  • Passengers in your vehicle at the time you were stopped by Police;
  • Challenges to police officer observations;
  • Constitutional Rights violations

 The evidence used to challenge a charge of impairment will differ depending on the unique circumstances of the case.

How Many Puffs does it Take to Cause Driving Impairment?

The short answer is that it is not possible to label exactly how many inhaled puffs it takes for one person to reach driving impairment, without knowledge of the variables.

The explanation is that the answer contains many variables.  For example, the marijuana strain, it’s concentration of THC, frequency and tolerance of the user, smoking pattern such as volume of THC upon each inhalation, length of time the user has been on Marijuana.

Much scientific and legal controversy surrounds this impairment issue. But one thing experts do agree upon agree is that it is also difficult to establish a relationship between a person’s  THC blood or plasma concentration and the impairing effects of Marijuana.

And while a urinalysis is one of the most common ways THC is detected in the body, they still do not test the level of impairment in the driver.

As a result, some of the 23 states that have legalized Marijuana have implemented a  per se limit which does not consider impairing effects.   This means a person can be driving without impairment, and still be arrested and prosecuted for DUI if those limits are exceeded.

Arizona does not have a statutory Marijuana per se limit. Though a common limit in some states that have legalized it, have a 5-nanograms-per-milliliter limit.

Some long term users find this unfair considering some long term, frequent users have built tolerances far greater than that amount, and have no driving impairment at that THC concentration level.

According to The National Highway Traffic  & Safety Administration (NHTSA) the potency of Marijuana is dependent on THC concentration and is usually expressed as a percentage of THC per dry weight of material.

Average THC concentration in marijuana is 1-5 percent. Though some forms of cannabis have concentrations of THC that range from  17 to 20 percent of THC.

The lower the percentage of THC, the more “hits” or “puffs” takes to reach a medicinal or desired effect.

The same would be true for how many puffs it takes to reach a level or impairment, or for example a 5 ng/ml threshold.

Though often argued to the contrary, some e studies suggest that a 5 ng/ml (nanograms per milliliter), THC level produces driving impairment equal to that of .05 percent alcohol Blood Alcohol Content Level (BAC).

Unlike alcohol, THC levels climb rapidly and spike after inhaling, then within an hour or two begin to fall.

So for some who take several puffs and then behind the wheel, they will be driving at 5 ng/ml THC level. But the level itself should not be a sole indicator of impairment.

The best assurance for safety is to refrain from driving under the influence of Marijuana re under the influence of Marijuana.

If that is not possible, it is important to be aware of how much THC is in your system. In light of this ruling, it is important to remain aware of its effects, limitations or impairments at certain levels.   It is best to become cognizant of these variables while a user is in a safe environment such as their home.

If you are a new user, it is important to discuss impairment issues related to your dosage and any impairing impacts with your medical practitioner or health care provider.

If you are a driving in Arizona but are qualified to use medical marijuana in another state it is important to understand the laws in all states for which you will be driving.

Criminal Defense for Marijuana DUI Charges Mesa AZ       

This ruling places a heavy and uncertain burden on medical marijuana users who are arrested and charged with driving under the influence. If you are charged, consult James E. Novak, a drug crimes defense attorney in Tempe, Arizona. Mr. Novak is a former prosecutor and experienced trial lawyer. If retained, he will provide you with a strong defense for your charges. We offer a free consultation for active criminal charges in Phoenix, Mesa, Tempe, Chandler, Gilbert, and Scottsdale, Arizona. Call today (480) 413-1499.

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