The Issue of Driving While a Relevant Drug, Δ9-tetrahydrocannabinol, Was Present in Saliva: Evidence About the Evidence


  • Laurence Mather


With the lawful use of medicinal cannabis becoming a closer reality across most of Australia, the matter of roadside testing and driving impairment will be of immediate concern to patients undergoing cannabinoid pharmacotherapy. Under current roadside testing laws, the same issues will pertain to the medical patient, who wishes or needs to drive, as to the ‘recreational’ cannabis user. While there is abundant public domain, scientific and medical literature, as well as published expert opinion, exploring the epidemiological, chemical and pharmacological research evidence of cannabis ingestion and driving, this paper analyses the evidence from roadside testing that is being used to support the notion that a driver may be ‘impaired’ or ‘driving under the influence’ of cannabis. By and large, the evidence undeniably shows that cannabis ingestion can impair driving. This paper however, comes to the pharmacological opinion that the current roadside testing of saliva/oral fluid for Δ9-tetrahydrocannabinol (THC), without other evidence, provides a poor predictor of impairment. This paper thus intends to stimulate re-evaluation of the present pharmacological criteria under which users of cannabis might be judged legally.