Researchers in the US have concluded it will take “more than a few years” to develop a reliable cannabis breathalyser after a study detected no discernibly different levels of THC in people’s breath before and after cannabis use.
Samples of breath aerosols – particles which form deep in the lungs after every inhale and exhale – were collected using an “impaction filter”.
A total of 12 participants were tested before cannabis use and then one hour after THC was consumed.
The findings were “somewhat similar”, with post-THC levels showing little variation to the pre-use samples.
Researchers said the study, conducted by the University of Colorado Boulder and the National Institute of Standards and Technology (NIST), illustrated the difficulty in developing reliable breathalyser technology.
NIST supervisory chemical engineer and study author Tara Lovestead said: “We were hoping to see if there was a difference in the amount of THC that we could collect in a participant’s breath before and after they used a legal market cannabis product. And we expected to see higher THC concentrations in samples that we know were taken one hour after they used.”
But the results did not vary, “adding to the complexity” of efforts to develop a reliable test.
“In many cases, we would not have been able to tell whether the person smoked within the last hour based on the concentration of THC in their breath,” Lovestead said.
“It means that our hypothesis that it is really hard to develop a cannabis breathalyser is correct. This is hard, and it’s going to take more than a few years of research.”
She said the goal is to develop the infrastructure that could identify whether somebody has recently used cannabis or might be impaired, and to “understand the physical and chemical properties of cannabis compounds so we can target them in breath collection devices”.
The study’s co-author and NIST materials research engineer Kavita Jeerage said: “A lot more research is needed to show that a cannabis breathalyser can produce useful results.
“A breathalyser test can have a huge impact on a person’s life, so people should have confidence that the results are accurate.”
NIST said the research remains “in its infancy” given the classification of cannabis as a schedule one controlled drug in the US.