What remains after the last bite of a cannabis-infused brownie? For scientists at the National Institute of Standards and Technology (NIST), the answer came in the form of a breath: for the first time, it was possible to detect cannabinoids in human breath after consuming edibles. 

The discovery, published this month in the Journal of Analytical Toxicology, marks an important step towards new field testing models, but also exposes the limits of science in the face of the complexity of the human body and the substances that inhabit it.

The study, considered a "proof of concept", involved 29 volunteers who ingested edibles containing THC in varying concentrations, from 5 to 100 mg. Breath samples were collected before and after consumption, at three different times: about 47, 92, and 180 minutes after ingestion. 

Interestingly, even before the first bite, 27 of the 29 participants already had detectable levels of THC in their breath. A reflection of what scientists call "persistent residues", a result of previous substance use, even after hours of abstinence. “The high rate of THC detection after 8 hours without use reminds us that a single measurement is unlikely to tell the whole story,” the researchers told Marijuana Moment.

A breathalyzer for cannabis?

The idea of a cannabis breathalyzer test is not new, but it still lacks scientific robustness. The NIST study reinforces that, although two-thirds of the participants showed an increase in THC levels after consuming edibles, the results varied widely: four people showed no change at all, and six showed a decrease in levels, despite just having consumed.

According to the project's researchers, detecting increases in THC in breath after cannabis ingestion represents an important, albeit initial, advancement. Jennifer Berry, a chemist and lead author of the article, points out that this finding, in itself, is scientifically relevant. However, Tara Lovestead, also a team member, notes that the devices used still lack rigorous standards to ensure accuracy and reliability, emphasizing that the development of this technology is still in a preliminary stage.

The difference between alcohol and cannabis

Unlike alcohol, for which there is a well-established relationship between blood concentration and psychomotor impairment, THC behaves more erratically. Several studies show that the concentration of THC in blood or breath does not directly correlate with the ability to drive or perform cognitive tasks. In other words, the same level of THC can mean completely different effects in occasional and chronic users.

According to a recent study published in The Lancet and conducted by researchers from Canada and the United States, no linear relationship was found between THC levels in the blood and driving ability. Experts explain that this difficulty arises from the fact that cannabinoids interact with the body uniquely, influenced by factors such as metabolism, frequency of use, type of product, and even the mode of ingestion.

The challenge of legislating subjectivity

With the increasing legalization of cannabis in various US states, the urgency to create legal and scientific devices to deal with the plant's use in situations like driving is inevitable. But how to legislate when time, the body, and the molecule follow their own rhythms?

The National Highway Traffic Safety Administration (NHTSA) itself recognized, as early as 2015, that “it is not advisable to try to predict the effects based solely on THC blood concentrations”.

To advance the investigations, NIST is set to hold a workshop in September with device manufacturers, the results of which will be compiled into a public report. According to Kavita Jeerage, also a scientist on the project, this step will begin to address fundamental questions, such as THC behavior after ingestion, the time needed for levels to return to baseline, and how to interpret the data obtained by a breathalyzer in a meaningful way.

With information from Marijuana Moment.