Legalise cannabis

Saliva – poor measure of Cannabis impairment

Researchers from the Lambert Initiative for Cannabinoid Therapeutics, University of Sydney, analysed studies on the relationship between driving performance and concentrations in blood and saliva of delta-9-tetrahydrocannabinol (THC). Results indicate blood and oral fluid THC concentrations are relatively poor or inconsistent indicators of cannabis-induced impairment. This contrasts with the much stronger relationship between blood alcohol concentrations and driving impairment.

Lead author Dr Danielle McCartney said: “Higher blood THC concentrations were only weakly associated with increased impairment in occasional cannabis users while no significant relationship was detected in regular cannabis users”. For infrequent, or occasional cannabis users, some significant correlations between oral fluid THC concentrations and impairment were observed. However, the researchers note most relationships were ‘weak’.

The research raises questions about the validity of methods used to assess cannabis-related impairment. This includes widespread ‘random’ mobile drug testing for THC in saliva. Researchers also found ‘subjective intoxication’ – how ‘stoned’ individuals reported they felt – was also only weakly associated with actual impairment. Thus, drivers should not necessarily rely on perception of their own impairment in deciding whether they are fit to drive.

Dr Thomas Arkell, also from the Lambert Initiative, said: “Individuals are better to wait a minimum length of time, between three and 10 hours, depending on the dose and route of administration, following cannabis use before performing safety-sensitive tasks”. Academic Director of the Lambert Initiative, Professor Iain McGregor, said: “A cannabis-inexperienced person can ingest a large oral dose of THC and be completely unfit to drive yet register extremely low blood and oral fluid THC concentrations”.

“On the other hand, an experienced cannabis user, might smoke a joint, show very high THC concentrations, but show little if any impairment. We clearly need more reliable ways of identifying cannabis-impairment on the roads and the workplace”. “This is a particularly pressing problem for the rapidly increasing number of patients in Australia who are using legal medicinal cannabis yet are prohibited from driving. The increase in legal recreational use of cannabis across multiple jurisdictions worldwide is also making the need for reform of cannabis-driving laws more urgent”.

Original source: THC in blood and saliva are poor measures of cannabis impairment

Study online 9 November 2021

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