Drivers who test positive for the presence of THC in blood are no more likely to be involved in motor vehicle crashes than are drug-free drivers, according to a federally sponsored case-control study involving some 9,000 participants. The study, published Friday by the United States National Highway Traffic Administration (NHTSA), is the first large-scale case-control study ever conducted in the United States to assess the crash risk associated with both drugs and alcohol use by drivers.
Authors reported that drivers who tested positive for any amount of THC possessed an unadjusted, elevated risk of accident of 25 percent (Odds Ratio=1.25) compared to controls (drivers who tested negative for any drug or alcohol). However, this elevated risk became insignificant (OR=1.05) after investigators adjusted for demographic variables, such as the drivers’ age and gender. After researchers controlled for both demographic variables and the presence of alcohol, THC-positive drivers’ elevated risk of accident was zero (OR=1).
By contrast, researchers reported that drivers who tested positive for low levels of alcohol possessed a statistically significant risk of accident, even after controlling for demographic variables (e.g., Drivers with a BAC of 0.03 possessed a 20 percent greater risk of motor vehicle accident [OR=1.20] compared to controls). Drivers with BAC levels of 0.05 possessed a greater than two-fold risk of accident (OR=2.07) while motorists with BAC levels of 0.08 possessed a nearly four-fold risk of accident (OR=3.93).
Researchers did not analyze drivers’ THC levels to similarly estimate whether higher or lower THC levels may impact crash risk in a dose-dependent manner, as has been previously reported in some separate analyses of fatal crash data.
Authors concluded, “This finding indicates that these other variables (age, gender, ethnicity, and alcohol use) were highly correlated with drug use and account for much of the increased (crash) risk associated with the use of illegal drugs and THC.”
The study’s finding contradict allegations by NIDA and others that “marijuana use more than doubles a driver’s risk of being in an accident,” but are largely consistent with those of a 2013 literature review published in the journal Accident Analysis and Prevention which reported that cannabis-positive drivers did not possess a statistically significant risk of a either fatal accident or a motor vehicle accident causing injury.
See NORML’s white paper on cannabis and psychomotor performance here.
The Arizona Supreme Court this week rejected a 1990 state law that classified the presence of inert THC metabolites in blood or urine as a per se traffic safety violation.
Carboxy-THC, the primary metabolite (breakdown product) of THC is not psychoactive. Because it is lipid soluble, the metabolite may remain detectable in blood or urine for periods of time that extend well beyond any suspected period of impairment. As a result, the US National Highway Traffic Safety Administration acknowledges, “It is … currently impossible to predict specific effects based on THC-COOH concentrations.”
Nonetheless, under Arizona law, the mere presence of carboxy THC — absent any evidence of behavioral impairment — was considered to be a criminal violation of the state’s traffic safety laws. (Delaware, Georgia, Illinois, Indiana, Iowa, Nevada, Ohio, Oklahoma, Rhode Island, and Utah impose similar statutes.) On Wednesday, the Court struck down the provision.
Writing for the majority, Justice Robert Brutinel opined: “The State’s interpretation that ‘its metabolite’ includes any byproduct of a drug listed in § 13-3401 found in a driver’s system leads to absurd results. … Most notably, this interpretation would create criminal liability regardless of how long the metabolite remains in the driver’s system or whether it has any impairing effect. For example, at oral argument the State acknowledged that, under its reading of the statute, if a metabolite could be detected five years after ingesting a proscribed drug, a driver who tested positive for trace elements of a non-impairing substance could be prosecuted.”
He added: “Additionally, this interpretation would criminalize otherwise legal conduct. In 2010, Arizona voters passed the Arizona Medical Marijuana Act (“AMMA”), legalizing marijuana for medicinal purposes. Despite the legality of such use, and because § 28-1381(A)(3) does not require the State to prove that the marijuana was illegally ingested, prosecutors can charge legal users under the (A)(3) provision. Because carboxy-THC can remain in the body for as many as twenty-eight to thirty days after ingestion, the State’s position suggests that a medical-marijuana user could face prosecution for driving any time nearly a month after they had legally ingested marijuana.”
The Court concluded: “Because the legislature intended to prevent impaired driving, we hold that the ‘metabolite’ reference in § 28-1381(A)(3) is limited to any of a proscribed substance’s metabolites that are capable of causing impairment. Accordingly, … drivers cannot be convicted of the (A)(3) offense based merely on the presence of a non-impairing metabolite that may reflect the prior usage of marijuana.”
The Court did not address provisions in the state’s per se DUI law outlawing the operation of a motor vehicle with any presence of THC in one’s blood even though, according to NHTSA, “It is difficult to establish a relationship between a person’s THC blood or plasma concentration and performance impairing effects.”
Study: Passage of Medical Marijuana Laws Associated With Reduced Incidences of Alcohol-Related Traffic FatalitiesAugust 13, 2013
The passage of medical cannabis laws is associated with a reduction in the public’s consumption of alcohol and with fewer incidences of alcohol-related traffic fatalities, according to data published in the Journal of Law and Economics.
Investigators at Montana State University, the University of Oregon, and the University of Colorado assessed data regarding both alcohol consumption and traffic fatality rates for the years 1990 to 2010.
Authors wrote: “Using individual-level data from the Behavioral Risk Factor Surveillance System (BRFSS) …, we find that MMLs (medical marijuana laws) are associated with decreases in the probability of [an individual] having consumed alcohol in the past month, binge drinking, and the number of drinks consumed.”
Researchers further acknowledged that this general decline in the public’s use of alcohol was likely responsible for a parallel decline in the number of alcohol-related traffic fatalities.
“Using data from FARS (federal Fatality Analysis Reporting System) for the period 1990–2010, we find that traffic fatalities fall by 8–11 percent the first full year after legalization. … Why does legalizing medical marijuana reduce traffic fatalities? Alcohol consumption appears to play a key role. The legalization of medical marijuana is associated with a 7.2 percent decrease in traffic fatalities in which there was no reported alcohol involvement, but this estimate is not statistically significant at conventional levels. In comparison, the legalization of medical marijuana is associated with a 13.2 percent decrease in fatalities in which at least one driver involved had a positive BAC level. The negative relationship between the legalization of medical marijuana and traffic fatalities involving alcohol lends support to the hypothesis that marijuana and alcohol are substitutes.”
Authors determined, “We conclude that alcohol is the likely mechanism through which the legalization of medical marijuana reduces traffic fatalities. However, this conclusion does not necessarily imply that driving under the influence of marijuana is safer than driving under the influence of alcohol. Alcohol is often consumed in restaurants and bars, while many states prohibit the use of medical marijuana in public. If marijuana consumption typically takes place at home or other private locations, then legalization could reduce traffic fatalities simply because marijuana users are less likely to drive while impaired.”
The abstract of the study, “Medical marijuana laws, traffic fatalities, and alcohol consumption,” is available free online here. NORML has several additional papers specific to the issue of cannabis and psychomotor performance available online here.
Members of the Oregon House and Senate have given final approval to two separate legislative measures, Senate Bill 40 and Senate Bill 82, to reduce penalties related to certain marijuana possession offenses.
Senate Bill 40 amends the criminal code to reclassify marijuana offenses involving the possession of over one ounce, but less than four ounces of marijuana, from a felony offense punishable by up to 10 years in prison, to a Class B misdemeanor. It also reclassifies offenses involving the possession of less than 1/4 ounce of hashish from a felony to a Class B misdemeanor. The measure also reduces the fine presently associated with civil violations involving the possession of less than one ounce of marijuana.
Senate Bill 82 eliminates the suspension of driving privileges for those cited civilly for possessing an ounce or less of marijuana.
Both bills now await action from Democrat Gov. John Kitzhaber. If signed into law, the changes will take effect immediately upon passage.
Oklahoma Gov. Mary Fallin has signed legislation, House Bill 1441, into law that criminalizes drivers from operating a motor vehicle if they have any detectable amount of THC and/or its inactive metabolites in their blood, saliva, or urine. Under such internal possession statutes, known as zero tolerance per se laws, a motorist who tests positive for the presence of such compounds is guilty per se (in fact) of a criminal traffic safety violation, regardless of whether or not there exist supporting evidence that the defendant was behaviorally impaired by such compounds.
Residual, low levels of THC may remain present in the blood of occasional consumers for several hours after past use and for several days in habitual consumers — long after any behavior-inducing effects of the substance have worn off. The inert carboxy-THC metabolite, a commonly screened for byproduct of THC, possesses a longer half-life in blood and also may be present in the urine of daily cannabis consumers for several weeks, or even months, after past use.
Oklahoma will become the 11th state to impose such a strict liability per se standard once the law takes effect on October 1, 2013. It is the third state this year to amend its traffic safety laws to include either per se thresholds or presumptive limits for cannabinoids.
Ten additional states – Arizona, Delaware, Georgia, Illinois, Indiana, Iowa, Michigan, Rhode Island, Utah, and Wisconsin – already impose zero tolerance per se thresholds for the presence of cannabinoids and/or their metabolites.
Five states impose non-zero-tolerant per se thresholds for cannabinoids in blood: Montana (5ng/ml — the new law, HB 168, signed in April, takes effect on October 1, 2013), Pennsylvania (1ng/ml), Ohio (2ng/ml), Nevada (2ng/ml) and Washington (5ng/ml).
Last month, Colorado lawmakers also approved legislation, effective as of July 1, 2013, stating that the presence of THC/blood levels above 5ng/ml “gives rise to permissible inference that the defendant was under the influence.”
However, according to the United States National Highway Transportation and Safety Administration (NHTSA): “It is difficult to establish a relationship between a person’s THC blood or plasma concentration and performance impairing effects. … It is inadvisable to try and predict effects based on blood THC concentrations alone.”
In addition, a 2013 academic review of per se drugged driving laws and their impact on road safety found “no evidence that per se drugged driving laws reduce traffic fatalities.”