USyd Study Finds MDT Saliva Tests For THC Return Inaccurate Results 20% Of The Time

Tests performed by Sydney University’s Lambert Initiative for Cannabinoid Therapeutics has found that roadside mobile saliva tests, used by police to test for traces of drugs, return inaccurate results more than 20% of the time when testing for THC.

Hundreds of tests were performed on drivers with varying levels of THC in their system in order to investigate the link between cannabis and driver impairment. Current police tests only look for traces of illegal substances – whether or not you’re impaired doesn’t particularly matter.

Previously, NSW Police have said they will still prosecute drivers who are legally using medicinal cannabis if they test positive when driving. In January, 2018, NSW Premier Gladys Berejiklian announced the state police would be doubling its roadside drug testing efforts.

The Lambert Initiative’s academic director, Iain McGregor, told the ABC the tests are particularly poor at determining when people have a lot of THC in their system. “They can be really stoned and getting a negative test,” he said.

McGregor was also alarmed by the amount of false positives that were recorded. A false positive is a result that indicates something being present when it’s not – in this case, the test had one participant who tested positive for THC when they were actually using a placebo.

“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,” said McGregor.

Just last month, a northern NSW woman successfully used a “passing smoking” defence to get off drug driving charges.  Nicole Spackman said she had not smoked cannabis but had visited a terminally ill neighbour who was smoking medicinal cannabis in her presence.

Magistrate David Heilpern ruled that scientists did not know everything about THC and its rate of absorption, adding that the prosecution did not provide enough evidence to refute Spackman’s claim.

The Lambert Initiative’s full study into cannabis and driving will be released in a little over a month.