Breathalyzers are devices originally developed to detect the concentration of alcohol in a person\u2019s bloodstream. Law enforcement agencies throughout the U.S. commonly use these devices as part of procedures designed to identify people driving while intoxicated. In a study published in December 2013 in the journal Clinical Chemistry and reported in May 2014 by study sponsors at the National Institute on Drug Abuse, a team of researchers from the U.S. and Sweden assessed the accuracy of a newly developed breathalyzer device intended to detect the presence of the popular recreational drug marijuana. Blood-alcohol content (BAC), also known as blood-alcohol concentration or blood-alcohol level, is the percentage of alcohol contained in any given sample of blood. In the U.S., a person is deemed legally intoxicated when his or her blood-alcohol level reaches 0.08 percent. However, people with a BAC of just 0.05 percent can experience degrees of mental and physical impairment that make it difficult to safely operate a motor vehicle. Direct measurement of a person\u2019s blood-alcohol content requires the use of a blood test and a subsequent laboratory analysis. However, law enforcement officials trying to identify intoxicated people in daily life have no practical way to perform this kind of direct testing. Instead, they rely on breathalyzers, which estimate a person\u2019s BAC based on the amount of alcohol he or she has in her breath. Depending on the jurisdiction under consideration, a high breathalyzer result can qualify as legal evidence of alcohol intoxication. Marijuana and Driving Marijuana use is becoming increasingly popular and socially acceptable throughout the U.S. Unfortunately, intake of the drug can have a negative impact on a range of mental and physical skills that play a critical role in the safe operation of a car or any other type of motor vehicle. Examples of these skills include the ability to think clearly, the ability to maintain focus and attention, the ability to accurately perceive changes in the surrounding environment, the ability to accurately make and use memories and the ability maintain adequate control over muscle coordination. There is considerable evidence to indicate that substantial numbers of Americans drive while under the influence of marijuana. For example, a project undertaken in 2007 by the National Highway Traffic Safety Administration revealed that roughly 8.7 percent of people who drive at night on the weekends have the drug in their systems. This is about 300 percent higher than the number of people who drive while legally intoxicated. Detecting Marijuana Use In the study published in Clinical Chemistry, researchers from the National Institute on Drug Abuse and Sweden\u2019s Karolinska University Hospital used a new breathalyzer device developed in Sweden, called a SensAbues, to measure the THC content in the breath of 13 regular marijuana users and 11 occasional users after each of these individuals smoked a marijuana cigarette with a fairly low THC content of 6.8 percent. (Average THC potency for the drug in the U.S. is over 14 percent.) The researchers also measured levels of two other related substances found in all forms of cannabis. Nearly an hour after smoking marijuana, all of the regular users of the drug had detectable levels of THC in their breath. The rate of detection fell steadily over the next three-plus hours, until THC was identifiable in the breath of only one individual. Almost 91 percent of the occasional marijuana users had detectable amounts of THC in their breath close to one hour after smoking the drug. However, two hours after smoking, none of the occasional users still had detectable THC levels in their breath. Just one of the study participants in the two groups registered detectable amounts of either of the two other marijuana ingredients at any point during testing. Based on their findings, the study\u2019s authors concluded that the SensAbues device or similar technologies may eventually play an important role in the detection of people driving under the influence of marijuana. However, they note that the time frame for detection is limited, especially in people who don\u2019t use marijuana regularly. Efforts are also under way to evaluate the usefulness of the SensAbues device in detecting other commonly abused drugs. Further research will be needed before the technology meets the standards for real-world use in any form.