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Study Report: Medical Cannabis And Driving

As medical (and recreational) cannabis becomes more widely available, the potential impacts on our roads are becoming a more pressing issue.

In some places, patients using medical cannabis (regardless of its type or dosage) are outright banned from driving, or not permitted to drive X hours after taking medications. Is this really necessary? It may well be – but it also depends on the type and dosage.

A recently published study compared the effects of tetrahydrocannabinol (THC)-dominant and THC/cannabidiol (CBD) equivalent cannabis on simulated driving and cognitive performance. The study was carried out by researchers from the Lambert Initiative for Cannabinoid Therapeutics at the University of Sydney.

For the testing, the following was delivered via vaporisation: 125 mg THC-dominant (11% THC; < 1% CBD), THC/CBD equivalent (11% THC, 11% CBD), or placebo (< 1% THC/CBD) cannabis.

The researchers found both THC-dominant and THC/CBD equivalent types increased lane weaving during a car-following task, but had little effect on other driving performance measures. However, performance was impaired on the Digit Symbol Substitution Task (DSST), Divided Attention Task (DAT) and Paced Auditory Serial Addition Task (PASAT), with worse results on the latter two tasks with THC/CBD equivalent cannabis.

This is particularly interesting as CBD has often been claimed as reducing some of the impairment caused by THC.

“Cannabis containing equivalent concentrations of CBD and THC appears no less impairing than THC-dominant cannabis, and in some circumstances, CBD may actually exacerbate THC-induced impairment,” states the study.

Cannabis effects on driving are not nearly as predictable as those of alcohol, said academic director of the Lambert Initiative Professor Iain McGregor, who also stated much more research on the issue is needed.

The study did not involve CBD-only cannabis. CBD is a non-intoxicating cannabinoid that can be found in high levels of some strains of industrial hemp; which also have low THC levels.

The study was published in the journal Psychopharmacology and can be viewed here.

The Lambert Initiative was set up in 2015 thanks to the generosity of Australian philanthropists Joy and Barry Lambert, who gifted AUD $33.7 million to the University of Sydney for the project.  The initiative’s main aim is to optimise safe and effective cannabinoid therapeutics and to research how cannabis can play a role in treating a variety of diseases and conditions.

Steven Gothrinet
Steven Gothrinet has been part of the Hemp Gazette in-house reporting team since 2015. Steven's broad interest in cannabis was initially fueled by the realisation of industrial hemp's versatility across multiple sectors. You can contact Steve here.

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