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Cruising the Highway: How to Avoid Getting Arrested and Convicted of a THC DUI – Part 3


This is the final installment in the three-part series discussing how to avoid getting hemmed up in a marijuana DUI charge. Part 1 of this series provided a general overview of Arizona’s DUI law as it pertains to cannabis and some basic tips on how to avoid triggering a DUI investigation during a traffic stop. Last month in Part 2, I went into more detail about how to finesse a traffic stop where the cop suspects impairment from cannabis because of odor or some other obvious indication of cannabis use. In this final Part 3 of the series, I am going to talk about the ins and outs of handling THC DUI charges.

If the driver does end up getting charged, then usually a formal misdemeanor complaint will be filed in a city court or justice court. I say “usually” because sometimes even a first offense DUI is charged as a felony “aggravated” DUI. For example, if the driver’s license is suspended or there is a child in the car. For the purposes of this article, we will assume that this is a standard first offense misdemeanor THC DUI charge. Incidentally, when misdemeanor charges are filed, there is also a separate administrative license suspension procedure that is initiated at ADOT. These administrative proceedings are also beyond the scope of this article.

As stated in the previous articles in this series, there are two types of THC related DUI charges. One alleges that the driver was impaired by THC while driving and the other alleges that the driver simply had THC or its active metabolite in her system at the time of driving, regardless of whether she was impaired. The latter charge is generally referred to as a DUI per se charge. For example, in Colorado, the per se level is 5 nanograms. In Arizona, however, the per se level is zero. Even 1 nanogram is enough. Thus, the driver will be found guilty if the jury finds that he had even a slightest trace of THC in his system.

So, let’s get down to it: what happens when a person ends up getting charged with a THC related DUI per se charge? When he is released from his arrest, he will be provided with a citation with a court date. If he does not receive a citation at that time, then he will get a summons and complaint in the mail telling him when to show up for his first court date, called an “arraignment.” The centerpiece of the state’s case against him will be the blood test result that alleges his THC or active THC metabolite level. According to an Arizona Supreme Court decision from just a few years ago called State v. Harris, the state must show that the THC metabolites were active (hydroxy THC) as opposed to inactive (carboxy THC) metabolites. Thus, if the driver charged with a DUI per se was not a registered medical marijuana patient at the time of driving, then all the prosecutor needs to prove to the jury is that the blood test is accurate and shows that the driver had THC or active THC metabolites in his system. Generally speaking, the only way to win such a trial is to show that the blood draw or testing procedures were not complied with, that the sample was contaminated, or that there was a break in the chain of custody of the blood sample. For this reason, the defense of a non-patient against a DUI per se charge is more often based on a pretrial motion to suppress evidence due to a violation of the driver’s constitutional rights. For example, the Motion will argue that the stop was not valid, that the traffic stop was converted into a DUI investigation without the requisite reasonable suspicion, or that the person was arrested without probable cause to believe that he was impaired. The asserted constitutional violation might also be that the officer did not allow the driver to consult with an attorney before deciding whether to submit to the blood draw, or that the driver was not given the proper instructions before making such a decision. The remedy for a constitutional violation is that the state is deprived of any evidence acquired as a result of the violation. This is called the Exclusionary Rule. I will not go into detail about these issues here as they would require many more pages than I am permitted.

Thankfully, unlike a non-patient, a registered medical marijuana patient does have a defense at trial against the THC related DUI per se charge. In a landmark case that I was involved in called State v. Dobson, the AZ Supreme Court held that medical marijuana patients have an affirmative defense under the AMMA against a DUI per se charge. Specifically, the Supreme Court found if a registered patient persuades the jury that the nanogram level of active THC in her system was insufficient to cause her to be impaired, then the jury must find her not guilty. The patient driver is required to prove this fact by a preponderance of the evidence, which means that she must prove that it was more likely than not (51%) that she was unimpaired by the THC. In a later case, the Supreme Court further explained that the patient driver does not have to prove that the THC level found in his system is insufficient to cause impairment in the general public, but rather all she must do is convince the jury that the THC level was not enough to cause her to be impaired. Thus, her testimony about her own personal experience with cannabis and how it influences her is a very important part of the defense.

Although subjective, evidence in the form of objective scientific studies about THC and its impairing effects (or lack thereof) is also helpful and a vital part of most cases, as well. Introducing and explaining scientific studies requires the assistance of a qualified expert witness who is familiar with the latest scientific research into the subject. For example, most people are familiar with how people develop a tolerance to substances that they use on a regular basis, but an expert witness is required to explain how a medical marijuana patient develops tolerance to the effects of THC and how tolerance affects impairment. I have personally learned a lot over the years from such experts. As it happens, there are two general kinds of tolerance, physiological and behavioral. Within those two general categories, there are more specific types of tolerance. All of this must be explained to the jurors, who usually only have a basic understanding of tolerance when they show up for the trial. That’s where the expert witness comes in.

It is important to understand that it is only illegal for a person to drive under the influence of a substance if that substance causes impairment. Obviously, not all substances do and some only cause impairment at higher levels. Take alcohol as an example. The average person can consume a couple glasses of wine without being impaired and not being over the .08 limit. But most will admit that they can feel the alcohol, meaning that they are under the influence. Some substances actually improve performance. For example, it is common knowledge that caffeine can help keep drivers alert and attentive to driving conditions. What is less known is that studies exploring THC tolerance show that persons who are regular cannabis consumers drive better than persons who are not under the influence of any substance at all. They tend to drive more slowly, put more distance between their car and the car in front of them, are less likely to engage in risky driving behavior, etc. In other words, for the experienced cannabis consumer, THC is a performance enhancing substance, not an impairing one. Further evidence of this phenomenon is the fact that many professional and Olympic athletes are regular consumers of cannabis. It is critical for the defense attorney and the expert witness to make sure that the jury understands and accepts these findings.

It is also important for the jury to understand how THC is metabolized. When someone smokes cannabis, the THC level in their body skyrockets and remains at that elevated level for about an hour before tapering off during the second hour. After two full hours after smoking or vaping, a person returns to base levels and the person is no longer under the influence. “Base level” refers to the level of active THC that a regular consumer will have when not under the influence. A regular consumer always has some active THC in her system. Typically, for the average patient, I have found that the average base level ranges between 5 and 15 nanograms.

If a person stops consuming cannabis and completely abstains, then THC and its active metabolite will still remain in that person’s blood for several days. Moreover, unlike alcohol, it is not eliminated from the system in a uniform and predictable manner. Because THC is stored in body fat, it is metabolized gradually and can be influenced by anything that affects a person’s metabolic rate. Studies show that over the course of 5 days, THC levels are erratic at any given point. On day one, the person may have 6 nanograms of THC. On day two that may drop to 3 nanograms, but then on day three the person may be back up to 5 nanograms. Scientists are still trying to understand how this process is influenced, but it seems that multiple variables are at work. One such variable that a recent study has discovered is the effect of stress hormones.

The stress related study was done by having rats consume cannabis and then after allowing their THC levels stabilize to base levels, the blood of the rats was tested, and their THC levels recorded. The scientists then injected a stress hormone into some of the rats and retested them. The results were that the THC levels of the rats who were not injected with the stress hormone remained the same, but the levels dramatically increased in the rats who were injected with the stress hormone. This “spiking” effect, as I call it, is a very important phenomenon in a DUI case because the one thing that most people report feeling when they are subjected to a DUI arrest is having felt high anxiety – being tense, nervous, upset, scared. According to the rat study, this intervening stressful event will cause the driver’s THC levels to shoot up. Thus, whatever a given patient driver’s THC level was at the time of driving, all we can say is that it was most likely much lower than it was at the time of the blood draw. Of course, if the driver was in an accident, we would expect there to be an even bigger influx of stress hormones thereby causing an even larger spike in the driver’s THC levels.

There are many other helpful studies about THC and driving that are beyond the purview of this article. Most people do not realize, for example, that our own National Highway Traffic Safety Administration (NHTSA) has performed huge meta-studies on cannabis use and driving behavior and come to the conclusion that, among other things, that there is no correlation between cannabis use and driving accidents. That would seem to confirm the studies mentioned above that found that cannabis use does not impair driving in regular consumers.

The affirmative defense established in Dobson has helped many patients avoid a THC related DUI per se conviction in Arizona. The patient driver must hire both an attorney and an expert witness, however, which means that lower income patients are often not financially capable of mounting an effective defense. Some courts will agree to pay for the expert if the defendant is not able to afford to defend himself, but many courts are reluctant to do so because of budgetary concerns. Like most defenses under AMMA, it is far from perfect, but better than no defense at all.

Incidentally, we expect that the Smart and Safe adult use initiative will appear on the ballot this November. If it passes, then there will be an even better defense: complete immunity from the THC related DUI per se charge for every adult over the age of 21. That would be much better than the affirmative defense under AMMA. In the meantime, the affirmative defense under AMMA is the only thing going. I will conclude by saying that a patient should always avoid driving within two hours of smoking or vaping cannabis. That is the window of potential impairment. Whatever the case, if medical marijuana patients read this article and the previous two installments in this series, and apply the suggestions and recommendations, then they will be in a good position to avoid being suspected of, charged with, or convicted of a THC related DUI.




Tom Dean has been a criminal defense lawyer since 1993 and has been winning marijuana cases in Arizona for over 20 years. Tom has represented persons charged with every kind of marijuana offense, including cultivation, transportation, sales, extraction, DUI, and simple possession. For more information about Tom Dean, visit his website.

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