Marijuana is a Schedule I drug that is illegal under Federal law. As of fall 2015, however, 23 States and the District of Columbia legalized the use of marijuana for medicinal purposes (Governing.com, 2015; ProCon.org, 2015), and 17 States and the District of Columbia had decriminalized the use of marijuana–typically meaning no prison time or criminal charge for first-time possession of a small amount for personal consumption (NORML, 2015). Additionally, four States–Alaska, Colorado, Oregon, and Washington–and the District of Columbia have passed laws legalizing the use of marijuana for recreational purposes. In November 2012, Washington and Colorado became the first States to pass voter initiatives to legalize recreational marijuana use by people 21 and older.5 In December 2012, Washington began implementing the provisions of legalization, which included: * the establishment of legal possession (1 ounce or less for private consumption), and amendment of the State’s driving under the influence statutes to include a per se limit for THC (5 ng/mL [nanograms per milliliter]); * regulation, taxation, and law enforcement authority over marijuana by the Washington State Liquor and Cannabis Board (formerly the Washington State Liquor Control Board); * a licensing system for retailers; and * a dedicated marijuana fund, with surplus revenues earmarked for research, health care, substance abuse prevention, and education. Under this new legislation, Washington became one of the first States to develop legal commercial systems to make nonmedicinal marijuana available to the general adult population. The first marijuana retail outlets opened on July 8, 2014. The recent liberalization of marijuana laws has raised public safety concerns, including whether increased access to marijuana leads to increased drugged-involved driving and motor vehicle crashes. Marijuana has a variety of effects on humans and can be associated with stimulant, sedative, and hallucinogenic effects. Both the experimental and epidemiologic evidence on cannabinoids’ effects on driving are mixed. Experimental studies. Studies of neurocognitive and psychomotor skills have examined whether THC, the active ingredient in marijuana, affects reaction time, hand-eye coordination, vigilance, time and distance perception, and multiple-task processing (Downey et al., 2013; Hartman & Huestis, 2013; Lenné et al., 2010). Because these skills are central to driving, these studies suggest that marijuana use may have a detrimental effect on motor vehicle operation. In a summary of experimental studies examining the effect of THC on driving performance, Penning et al. (2010) concluded that THC alone impairs driving performance to some extent, whereas THC in combination with alcohol has a more pronounced effect. Laboratory studies and reviews have found evidence that cannabis use impairs driving-related skills (NCPIC, 2014). These studies indicate that performance decrements are generally dose-related and typically persist for 2 to 4 hours after consumption (Ashton, 1999; Ramaekers, Kauert, et al., 2006; Ramaekers, Moeller, et al., 2006). Although laboratory studies provide a first step in determining whether marijuana has a potential impairing effect on drivingrelated tasks, these studies do not provide a direct association between THC use and driving performance. Epidemiologic studies can help address questions about the frequency with which people drive with cannabis in their systems and the extent to which crash risk is increased. Several types of studies provide data to address these questions, including selfreport data on substance use and driving, roadside surveys of representative samples of drivers that involve collecting and analyzing biological specimens, and studies of substance use among crash-involved and non-crash-involved drivers. Few nationally representative surveys have gathered data on self-reported cannabis use and driving. However, crash risk studies have used drivers’ self-reports of cannabis use. Using self-report data alone can be problematic because the resulting data may be subject to over- or under-reporting as a result of social desirability biases, suspicion that the data will not be anonymous or confidential, and recall biases (Compton, Vegega, & Smither, 2009). Roadside surveys often include self-report data along with biological specimens (e.g., oral fluid and/or blood) that can be used to validate the self-report data on drug use. These biological markers can also provide direct information about the presence and concentration of drugs in drivers’ systems. Comparisons of the presence of THC among U.S. drivers, as measured in oral fluid and/or blood in two national roadside surveys conducted by NHTSA in 2007 and 2013—2014, show that the percentage of THC-positive nighttime weekend drivers increased from 8.6 percent in 2007 to 12.6 percent in 2013—2014, a 47 percent proportional increase (Berning, Compton, & Wochinger, 2015). Although the presence of drugs in biological specimens does not necessarily demonstrate impairment, the findings suggest increased THC use among drivers over time. Although studies of the frequency of drug use among crash-involved drivers provide valuable descriptive data, the inference that drug use increases crash risk requires studies that consider drug use among crash-involved versus non-crash-involved drivers. Several types of crash studies have been used to estimate risk (Compton & Berning, 2015). Culpability studies compare the rates at which drug-positive crash-involved drivers versus drug-negative crash-involved drivers are found to be at fault in their crashes. Case-control studies compare drug use by crash-involved drivers to drug use by non-crash-involved drivers and provide controls over some variables that may introduce bias in risk estimates. As noted by several reviews (Compton & Berning, 2015; NCPIC, 2014), existing epidemiological studies (both culpability and case-control) have yielded contradictory estimates of marijuana use and crash risk, with some suggesting minimal or no effect on crash risk and others estimating a small increase in crash risk. Changes in laws provide a natural experiment for investigating whether policy changes that make marijuana more accessible are associated with changes over time in THC-positive driving. In relation to Initiative 502, which legalized the recreational use of marijuana, a study on blood analyses in the Washington State toxicology laboratory (Couper & Peterson, 2014) examined the prevalence of THC among suspected impaired drivers in the State. Specifically, the prevalence of both active THC (THC and 11-OH-THC) and the inactive metabolite carboxy-THC (THC-COOH) were compared pre- and post-legalization. Before legalization (2009 to 2012), the average annual percentages of cases positive for THC and carboxy-THC were 19.1 percent and 27.9 percent, respectively. By 2013, these percentages had significantly increased to 24.9 percent and 40.0 percent, respectively (p < .05). The prevalence of alcohol, and the majority of other drugs from blood toxicology results of suspected impaired drivers, did not change significantly over the 5-year period. However, it should be noted that there may be other factors that may have affected these results. Among heavy, habitual users, THC may be found in the blood days after consumption; thus, there is the possibility that some of the THC-positives are unrelated to the driving event. This study examined the prevalence of alcohol- and drug-positive drivers in Washington State, on Fridays, and Friday and Saturday nights. Of special interest was any change in the percentage THC-positive drivers before and after the implementation of legalized retail sales of recreational marijuana. (Author/publisher)
Samenvatting