According to the National Institute on Drug Abuse, THC affects areas of the brain that control the body's movements, balance, coordination, memory, and judgment, as well as sensations. Because these effects are multifaceted, more research is required to understand marijuana's impact on the ability of drivers to react to complex and unpredictable situations. However, we do know that—
- A meta-analysis of approximately 60 experimental studies—including laboratory, driving simulator, and on-road experiments—found that behavioral and cognitive skills related to driving performance were impaired in a dose-dependent fashion with increasing THC blood levels. (Berghaus G, Sheer N, Schmidt P. Effects of cannabis on psychomotor skills and driving performance–A meta-analysis of experimental studies. In CN Kloeden and AJ McLean (eds.), Proceedings of the 13th International Conference on Alcohol, Drugs and Traffic Safety. Adelaide, Australia: The University of Adelaide, NHMRC Road Accident Research Unit, pp. 403–409, 1995.)
- Evidence from both real and simulated driving studies indicates that marijuana can negatively affect a driver's attentiveness, perception of time and speed, and ability to draw on information obtained from past experiences.
- A study of over 3,000 fatally injured drivers in Australia showed that when marijuana was present in the blood of the driver, he or she was much more likely to be at fault for the accident. Additionally, the higher the THC concentration, the more likely the driver was to be culpable. (Drummer OH, Gerostamoulos J, Batziris H, Chu M, Caplehorn J, Robertson MD, Swann P. The involvement of drugs in drivers of motor vehicles killed in Australian road traffic crashes. Accid Anal Prev 36(2):239–248, 2004.)
- Research shows that impairment increases significantly when marijuana use is combined with alcohol (National Highway Traffic Safety Administration. Marijuana and alcohol combined severely impede driving performance. Ann Emer Med 35(4):398–399, 2000). Studies have found that many drivers who test positive for alcohol also test positive for THC, making it clear that drinking and drugged driving are often linked behaviors.
Arizona's implied consent law now allows an offer to issue an order of suspension if they believe that a person is operating a motor vehicle with any detectable level of a prohibited drug, or its metabolites, in that person's blood. The results do not have to be immediately available.
If you find yourself in this situation, call The Law Office of Craig W. Penrod for more information. Craig has been involved in criminal and DUI defense for more than 30 years, is certified by the State Bar of Arizona as a Certified Criminal Law Specialist, is AV® rated, the highest rating by Martindale Hubbell®, is listed in the Bar Register of Preeminent Lawyers®, and has been selected for inclusion in Southwest Super Lawyers™ Editions 2008, 2009, 2010, 2011 and 2012. Contact the lawyers at the Law Offices of Craig W. Penrod for a free initial legal consultation if you find yourself facing DUI or criminal charges.