"As a rule of thumb, if you're smoking [pot], wait at least six hours before driving," warns the Colorado Department of Health. "If you're ingesting, wait at least eight."
Mass spectrometry has been the gold standard for making laboratory measurements on breath samples because of the tool's extreme sensitivity. But, because mass spectrometry devices are large, expensive instruments – table-top or even larger – they're not practical to take into the field. That's why, Heanue says, Hound Labs developed a technique that is portable and that has the same sensitivity as mass spectrometry. "In fact," he says, "the way we validate our device is to do measurements with both our technology and mass spec and show that they yield comparable results. Mass spec has been a critical tool for us."
Though there are other THC breathalyzers in development – notably one from Cannabix Technologies, in Vancouver, Canada – nothing is ready to go on the market right now. "We're all waiting," Says Huestis. "When they have something, we scientists are going to say, prove to me that you don't have false positives. Prove to me that you don't have false negatives. Tell me when you can first start detecting it in breath, tell me when you last detect it in breath. What's the detection window? How are you confirming? We have a lot of questions [but] we're ready and we're excited. And if it works I think it's going to be a great tool."
Others, though, are feeling a bit more cautious with their optimism. Heather Thompson holds a PhD in molecular and chemical biology and is a cannabis educator and advocate based in Colorado. She agrees that breathalyzers would be a better tool than checking serum levels via blood, urine, or oral fluids because of the likelihood that they have to implicate chronic, frequent users even when they're not actually high. But, her concerns around any tests for impairment mostly center around bias – and who gets flagged for the testing of impairment to begin with.
"I just worry about the impact that that has on marginalized communities because it does impact them more than dominant communities," says Thompson. The rules about impairment, she says, are predominantly determined by white people. "And marginalized folks get screwed by that over and over."