Law enforcement officers have long relied on breathalyzer technology as an on-the-spot roadside detection test for alcohol ingestion, but can similar technology ever be used to identify recent cannabis ingestion? A recent study indicates that the answer may be "yes."
 
Investigators at the National Institutes on Drug Abuse (NIDA) in Baltimore, Maryland and the Karolinska University Hospital in Stockholm, Sweden conducted breath assessments of 24 self-identified cannabis consumers. Subjects each inhaled one standardized cannabis cigarette of 6.8% THC and then exhaled into a breath pad at various periods of time over the following several hours. Researchers sought to identify whether detectable levels of delta-9-THC, its primary metabolite THC-COOH, or cannabinol (CBN), a non-psychoactive cannabinoid, could be recovered in the breath pads and, if so, for how long.
 
Researchers reported the ability to accurately identify the presence of THC in both occasional and in regular consumers for limited periods of time following subjects’ inhalation of marijuana. THC remained present in the exhaled breath of habitual users for longer periods of time than it did in those who only used occasionally. Authors concluded: “Among chronic smokers (n = 13), all breath samples were positive for THC at 0.89 hours, 76.9 percent at 1.38 hours, and 53.8 percent at 2.38 hours, and only one sample was positive at 4.2 hours after smoking.  Among occasional smokers (n = 11), 90.9 percent of breath samples were THC-positive at 0.95 hours and 63.6 percent at 1.49 hours. One occasional smoker had no detectable THC.”
 
No samples tested positive for the presence of the carboxy THC metabolite and only one subject tested positive for the presence of CBN.
 
An abstract of the study appears online in the journal Clinical Chemistry here.
 
The NIDA study is not the first to establish that breath collection technology is sensitive to the presence of THC in those who have recently consumed cannabis as well as other controlled substances. Writing in the April edition of the Journal of Breath Research, Swedish researchers reported that analytes of THC, as well as cocaine, methamphetamine, morphine, methadone and other drugs, can be identified in subjects’ breath for up to a period of 24 hours following drug ingestion. Specific to THC, the researchers reported that breath analysis identified the substance in 89% (eight of nine) subjects who reported recent pot inhalation.
 
Authors of both studies said that their findings confirmed the potential for using exhaled breath analysis as an alternative specimen matrix for toxicological analysis, with NIDA’s researchers speculating that the technology may possess applicability for identifying “recent driving under the influence of cannabis,” but the latter assumption would appear to be premature.
 
First, breath test technology is simply a detection test, not a per se indicator of whether subjects are "under the influence" of drugs. To date, no such data exists correlating THC/breath detection levels with behavioral impairment (such as Breathalyzer detection of alcohol at levels above .08 in blood have been correlated as valid predictors of alcohol-induced driver impairment). In fact, neither study even attempted to correlate the detection of THC in breath with actual behavioral or psychomotor impairment of any kind.
 
Further, alcohol remains unique among drugs in its predictability, both in its pharmacokinetics (drug metabolization by the body) and behavioral effects. As a result, the United States National Highway Traffic Safety Administration (NHTSA) acknowledges: “Toxicology has some important limitations. One limitation is that, with the exception of alcohol, toxicology cannot produce ‘per se’ proof of impairment.” So while it is possible that breathalyzer drug technology may pose certain potential advantages (e.g., it can be administered on site rather than post arrest hours later) over urine or blood specimen collection, two matrixes that are notoriously unreliable for establishing either behavioral impairment or recency of drug use, it is unlikely to provide any direct or definitive evidence of whether or not one is driving under the influence of cannabis or anything else.