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  • September 16, 2015

    What is the Law on Driving Under the Influence of Marijuana in Wisconsin?

    Wisconsin has a zero-tolerance policy when it comes to driving with trace amounts of marijuana “metabolites” in the blood. No impairment is required. But one OWI-DUI lawyer says the law should change to reflect changing attitudes on marijuana.

    Joe Forward

    marijuana plantSept. 16, 2015 – Marijuana legalization is a hot topic. Recreational use is now legal in four states and Washington D.C., and 23 states allow it for medicinal purposes. However, marijuana use is still illegal in Wisconsin, and penalties apply for driving high.

    But Milwaukee attorney Lauren Stuckert, who specializes in OWI-DUI litigation at Mishlove & Stuckert, says Wisconsin should reevaluate its “drugged driving” laws.

    Under Wisconsin law, Wis. Stat. section 346.63(1), it’s against the law to drive with a “detectable amount” of a restricted controlled substance in the blood. Those who do are subject to the same penalties as those who drive over the legal limit for alcohol.

    When a person is suspected of driving under the influence of marijuana in Wisconsin, blood is tested for a metabolite called delta-9-tetrahydrocannabinol (delta-9-THC), the substance found in marijuana known to cause impairment or impaired perceptions.

    But Wisconsin does not require proof of “impairment” to convict for driving under the influence of marijuana. All that is required is a detectable amount of delta-9-THC. This “zero-tolerance” law allows individuals to be convicted with very small but detectable amounts.

    “Someone who used marijuana two days prior to driving could have a ‘detectable amount’ in their blood and not be impaired," Stuckert said. "But he or she would be treated the same as someone who was driving well over the legal limit for alcohol.”

    Different Laws on Drugged Driving

    A majority of states apply an “effect-based” approach to drugged driving, requiring prosecutors to show a driver was impaired by a controlled substance such as THC.

    However, at least one article, in the Injury Epidemiology Journal (IEJ), has noted that enforcing effect-based laws is difficult and complex, “particularly due to the lack of standardization in methods of assessing and determining drug-induced impairment.”1

    Currently, the primary method of assessing a driver’s drug impairment involves training on drug recognition, which allows trained law enforcement to identify signs of impairment, such as bloodshot eyes, nervousness, or other physical identifiers.  

    Other states have per se drugged driving laws. Drivers are presumed to be impaired if a blood test shows a specified level of THC metabolites in the blood. For instance, in Colorado and Washington, the legal limit for delta-9-THC is 5.0 nanograms per milliliter (ng/mL) of blood. A blood test that shows less than 5.0 ng/mL would not generally give rise to prosecution in those states, subject to exceptions.

    The IEJ article notes that states considering drugged driving laws with a per se legal limit should consider certain factors, such as “a driver’s mode of marijuana consumption, frequency of use, and the concurrent use of marijuana with other drugs.” 

    Other states, including Wisconsin, have zero-tolerance laws that don’t require a showing of impairment. And detectable trace amounts of delta-9-THC, as low as 1.0 ng/mL (one-billionth of a gram) can give rise to the same consequences for driving with a blood alcohol concentration (BAC) above 0.08, the level at which drivers are deemed impaired.

    The IEJ article also noted problems with zero-tolerance laws, concluding they can incriminate drivers who may not be impaired. “This issue is exacerbated for marijuana use,” notes the article, “Establishing Legal Limits for Driving Under the Influence of Marijuana.”

    “Due to its relatively long half-life, THC can be detected in the blood and urine of an individual for hours to days and for days to months following marijuana use, respectively, depending on the frequency of use and other factors,” the article notes.

    Other types of THC metabolites may remain in the blood longer than delta-9-THC, which typically does not stay in the blood long for occasional users (but can be longer for chronic users). 

    Threshold limits are the bigger question for states like Wisconsin, where prosecutors must prove the detectable presence of delta-9-THC specifically but showing actual impairment is not required.

    Law has Survived Constitutional Challenge

    Wisconsin’s zero-tolerance law has repeatedly survived constitutional challenge. Back in 2005, Joseph Smet challenged his conviction for operating a motor vehicle with a detectable amount of delta-9-THC in his blood. Smet facially challenged the constitutionality of the drugged driving statute, but a state appeals court upheld the law.

    A blood test revealed that Smet had 3.2 ng/mL of delta-9-THC in his blood. Smet said the law was unconstitutional because it did not require a showing of impairment, but the appeals court said “proof of impairment is not necessary.”

    “[A] particular driver with a detectable amount of a restricted controlled substance in his or her blood may or may not be impaired on a given occasion,” wrote Judge Neal Nettesheim for the three-judge panel in State v. Smet, a published opinion.

    “Nonetheless, the legislature reasonably and rationally could have determined that, as a class, those who drive with unprescribed illegal chemicals in their blood represent a threat to public safety,” Judge Nettesheim continued.

    The three-judge panel also rejected Smet’s equal protection argument. Smet argued that the drugged driving law treats a class of drivers differently than similarly situated drivers, those drunk drivers whose convictions must rest on a showing of impairment.

    “Smet’s disparate treatment argument first stumbles because it is based on the faulty premise that ‘driving under the influence’ means impairment. It does not, as we have already demonstrated,” wrote Judge Nettesheim for the three-judge panel.

    The Wisconsin Supreme Court denied review of Smet in 2006. However, the supreme court affirmed Smet this year in State v. Luedtke and State Weissinger (consolidated).

    The supreme court noted that drugs can range in purity and potency, and the legislature could reasonably conclude that banning any detectable amount was necessary, in part because “no reliable measure of impairment exists for many illicit drugs.”

    This statement leads to the question: would the court’s analysis change if reliable scientific measurements could determine whether a person was actually impaired?

    Joe ForwardJoe Forward, Saint Louis Univ. School of Law 2010, is a legal writer for the State Bar of Wisconsin, Madison. He can be reached by email or by phone at (608) 250-6161.

    In Luedtke/Weissinger, the court also rejected the claim that the statute is unconstitutional in cases where a driver did not knowingly ingest a drug, which makes the law a strict liability offense, unless the person had a valid prescription.

    This holding may apply, for instance, to a person who unknowingly inhaled second-hand marijuana smoke and then drove with a detectable amount of delta-9-THC in his or her blood. And a blood draw could still be warranted despite passing a field sobriety test.

    State law reflects the public’s no-tolerance policy on drugged driving in a state where, unlike alcohol, using marijuana and other drugs is illegal without a prescription.

    But Stuckert says the law should be reevaluated, given the fact that marijuana use is becoming more acceptable in the U.S., including Wisconsin (see sidebar, "Winds of Change on Marijuana Use.").

    She said in low-level THC cases without the concurrent presence of other drugs or alcohol, the punishment does not necessarily fit the crime, and defendants aren’t always protected from the errors that can occur during the delta-9-THC testing process.

    View from the Trenches

    Stuckert has represented individuals charged with as little as 1.0 ng/mL of delta-9-THC. The absence of an impairment requirement and the difficulty in testing small amounts of delta-9 THC leads Stuckert to believe that Wisconsin’s law on “drugged driving” needs to change.

    “No peer-reviewed scientific evidence has concluded that levels under 5.0 nanograms of the delta-9 metabolite are capable of causing impairment,” Stuckert said. “And chronic users may always have a detectable amount, even if they haven’t used in days.”

    Stuckert noted the concern that the Legislature allows testing labs to set their own cutoff levels, “with essentially zero oversight.” For instance, the Wisconsin State Laboratory of Hygiene [WSLH], which handles a majority OWI driving cases involving blood draws, has set a cutoff level of 1.0 ng/mL for delta-9-THC.

    “Analysis of past THC blood tests by experts in the field have led to serious doubts that the lab is able to accurately test blood for delta-9 at such a low level,” she said.

    The WSLH improved its delta-9-THC testing methods in 2013, she says, moving from a liquid to gas chromatography/mass spectrometry testing method. However, given the complexities involved in blood drug testing, Stuckert says Wisconsin’s testing process does not adequately protect against the potential loss of individual liberty.

    “The testing process for drugs in blood is far more complex and analyst-specific than blood testing for alcohol,” she said. “The procedures for THC blood testing are inadequate for low-level determinations.” 

    Amy Miles, director of the Forensic Toxicology Section at WSLH, says the lab has performed a rigorous validation process for THC testing and is “confident in the limit of detection and quantitation.” Miles says “manual integration” is rarely used, and “the instrument used to test samples for THC is very sensitive at low concentrations.”

    “During audits conducted by our accrediting agency, the American Board of Forensic Toxicology (ABFT), it has continuously concluded our methods are properly validated and the THC concentrations we report are accurate,” Miles said in an email.

    According to Miles, the WSLH is not alone in using the 1.0 ng/mL cutoff concentration, and that level is not the lowest used by other labs. “It is up to each individual laboratory to determine the appropriate cutoff concentrations, something we take very seriously and do not do without scientific validation and approval by ABFT,” Miles said.

    Stuckert notes that WSLH has generally complied with her requests for documents under Wisconsin’s Open Records law, which has allowed her to successfully attack the delta-9-THC testing process in some cases, at times with the aid of experts.

    “But not everybody can afford to have an expert come in and testify at a jury trial,” said Stuckert. “And if you don’t know how to cross-examine a lab analyst, and you don’t understand the science, it’s next to impossible to appropriately defend these cases.”

    “Notwithstanding the WSLH’s claim of outside oversight by the ABFT, we have seen instances of carryover – one sample contributing to the next – a consistent failure to include blanks between samples, and inappropriate manual integration in its testing for delta-9 THC,” Stuckert said.

    “The Wisconsin legal system empowers the laboratory itself to determine the level of delta-9 deemed unlawful, thus eliminating an important layer of objectivity that is critical to ensure a fair criminal justice system.”


    1 Wong et al., Establishing Legal Limits for Driving Under the Influence of Marijuana, Injury Epidemiology (2014), 1:26.

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