Some great statements regarding marijuana impairment and how it metabolizes in a recent article
“Technically, is it possible to measure THC in breath? Yes,” said Barry Sample, a board-certified toxicologist, senior director of science and technology for New Jersey-based Quest Diagnostics and manager of the lab’s employer drug testing division. “There’s been some early work on that. The problem is [there is]no consensus level even in blood as to what constitutes impairment.”
When it is smoked, 10 percent of marijuana is converted to active metabolite. But in edible form, 50 percent is converted to active metabolite. This means when metabolites are tested in the urine or hair, an edible product would result in more metabolites. Variables like these are why there is a lack of consensus on testing parameters to determine what constitutes intoxication. Recreational-use statutes designate levels for THC limits in the blood, but these vary by state, Sample said.