By Zoe Zaczek For Daily Mail Australia
Published: 06:57 BST, 23 May 2019 | Updated: 08:31 BST, 23 May 2019
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Drug driving tests have been called into question after a driver taking a placebo tested positive to cannabis.
University of Sydney researchers found roadside mobile saliva tests for tetrahydrocannabinol (THC) were inaccurate more than 20 per cent of the time.
In some instances, participants who were high on the drug tested negative while others who hadn't smoked in extended periods recorded false positives.
The validity of drug driving tests have been called into question after a landmark case found a woman who tested positive to cannabis use had passively smoked the drug
'We had someone test positive for THC who was using a placebo,' lead researcher Professor Ian McGregor told ABC News.
The research showed THC, which is responsible for cannabis' effect on the mind, is difficult to test, especially in large doses.
'The tests are particularly poor at detecting when people have a lot of THC in their system so they can be really stoned and getting a negative test,' Mr McGregor said.
More alarmingly, some participants were handed false positive results.
'We found on occasion the tests gave a false positive when people have very low levels of THC and that is a concern for the carriage of justice, people are not impaired and they have not had cannabis for quite a long time,' Mr McGregor said.
