Indeterminacy of Cannabis Impairment and ∆9-Tetrahydrocannabinol (∆9-THC) Levels in Blood and Breath

Abstract

Previous investigators have found no clear relationship between specific blood concentrations of D9-tetrahydrocannabinol (D9-THC) and impairment, and thus no scientific justification for use of legal “per se” D9-THC blood concentration limits. Analyzing blood from 30 subjects showed D9-THC concentrations that exceeded 5 ng/mL in 16 of the 30 subjects following a 12-hour period of abstinence in the absence of any impairment. In blood and exhaled breath samples collected from a group of 34 subjects at baseline prior to smoking, increasing breath D9-THC levels were related to increasing blood levels in the absence of impairment, suggesting that single measurements of D9-THC in breath, as is blood, are not related to impairment. When post-smoking duration of impairment was compared to baseline D9-THC blood concentrations, subjects with the highest baseline D9-THC levels tended to have the shortest duration of impairment. It was further shown that subjects with the shortest duration of impairment also tended to have the lowest incidence of horizontal gaze nystagmus at 3 h post-smoking. Finally, analysis of breath samples from these subjects revealed the presence of transient cannabinoids such as cannabigerol, cannabichromene, and D9-tetrahydrocannabivarin during the peak impairment window, suggesting that these compounds may be key indicators of recent cannabis use through inhalation. In conclusion, these results provide further evidence that single measurements of D9-THC in blood, and now in exhaled breath, do not correlate with impairment following inhalation, and that other cannabinoids may be key indicators of recent cannabis inhalation.