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Robert DuPontMark GoldRobert L. DuPont, M.D., is president of the Institute for Behavior and Health, Inc., and clinical professor of psychiatry at Georgetown University Medical School. He was the first director of the National Institute on Drug Abuse and second White House drug chief.
Mark S. Gold, M.D., is the Dizney Eminent Scholar, University of Florida Distinguished Alumni Professor, and chairman of psychiatry at the University of Florida, College of Medicine, McKnight Brain Institute.

Everyone knows alcohol and driving don’t mix, but what about drugs and driving? Few drivers know that it is illegal to drive under the influence of a drug, no matter what that drug is, including marijuana, other illicit drugs, prescription drugs, and over-the-counter drugs. When taking drugs alone or with alcohol, drugged drivers are putting themselves and others on the road at serious risk.

Drugged driving is a major highway threat today. In 2007 about one in six (16%) weekend nighttime drivers tested positive for a potentially impairing drug. Half of those (8%) were positive for marijuana.

The presence of a drug in drivers triples crash risk, and using alcohol increases this risk even more dramatically. In 2009, one in three fatally injured drivers tested positive for one or more drugs. It is no surprise that individual studies of injured drivers have found similar results. A study of seriously injured drivers admitted to a shock-trauma center found 30 percent positive for alcohol but 50 percent positive for drugs. Over one-quarter (26%) of all seriously injured drivers tested positive for marijuana.

An expanding body of literature has documented the seriously impairing effects of marijuana on cognitive function and psychomotor skills. Smoking marijuana doubles the risk of crash. Recent research has demonstrated that chronic daily marijuana smokers display impairment even after three weeks of abstinence. This is particularly concerning given the legalization of marijuana for adults in Colorado and Washington.

Medical MarijuanaTo address marijuana-impaired driving, these states have specific blood limits of 5 ng/mL tetrahydrocannabinol (THC) for drivers age 21 and older. But in fact there is no blood impairment threshold for marijuana or any other drug because, unlike alcohol, consistent relationships between drug blood concentrations and impairment do not exist. The implications of these laws are vast. Data released from the Washington State Toxicology Laboratory showed that, for the first six months of 2013, 43% of drivers arrested for impaired driving who tested positive for marijuana were below 5 ng/mL THC. Similarly, in 2012, 72% of Colorado drivers arrested for impaired driving that were positive for marijuana tested below 5 ng/mL THC. These drivers arrested for impairment who test positive for marijuana will likely not be prosecuted, putting others on the road at risk.

Reducing drugged driving has recently been identified as a national priority by the federal government. There is no simple solution. Law enforcement efforts are focused on better identification of drugs among individuals arrested for impaired driving. States are encouraged to pass zero tolerance laws where the presence of a drug (not prescribed to the driver) is a violation.

As with drunk driving, it will take massive public education and far more effective enforcement to turn back the tide of drugged driving. Drugged driving is a global problem; other countries have passed drug testing laws and implemented media campaigns, including in Australia and New Zealand which focus on marijuana-impaired driving. In the United States, the changing legal status of marijuana and the likely resulting increased prevalence of marijuana-impaired drivers on the roads pose a significant threat to public safety. For individuals using potentially impairing drugs as directed by their prescriber, it means understanding how a drug affects you before driving and using caution. We encourage you to discuss this with your physician.

Analogous to the familiar admonition “Don’t Drink and Drive,” we need the clear message “Don’t Use Drugs and Drive.” Reducing drugged driving will save lives.