Drug Free Australia disputes saliva testing at 50ng/ml
A proposed 50ng/ml cannabis threshold in NSW roadside saliva testing is facing criticism from Drug Free Australia, which argues the level does not match driver impairment.
Under the NSW Government plan, drivers below the 50ng/ml threshold could receive warnings if they hold a medical cannabis prescription.
Drug Free Australia argues that scientific studies link even 1ng/ml in saliva with cannabis driver impairment. It also points to evidence that vaporised cannabis can impair driving for 5 to 7 hours, while oral use can last for some hours longer.
2019 THC study
Studies of THC in blood and saliva show 80% to 90% of the drug is eliminated within the first 1 to 2 hours. However, impairment can continue for at least 3 hours after that because THC is rapidly absorbed by the brain.
In a 2019 study, 17 subjects inhaled 25mg of THC. Only 5 recorded levels above 50ng/ml at 60 minutes, and just 1 remained above that level after 2 hours.
After 4 hours, 59% of participants had saliva readings of 1 to 2ng/ml, even though impairment was expected to last at least another hour. Drug Free Australia uses that result to argue that low saliva readings do not mean low impairment.
Another study tested oral THC capsules at 62.5mg and 125mg. It found no THC in saliva, a result the group says shows a driver could be impaired while returning a zero saliva reading.
That same study suggested waiting 9 to 10 hours before driving after taking the capsules. Because THC in the blood does not migrate into saliva, the group says saliva testing cannot reliably measure impairment from oral doses.
Drug Free Australia has also referred NSW politicians to Colorado data. Shopfront medical cannabis began there in 2009, and the group says monthly cannabis use rose 54% by 2019.
Over the same period, cannabis driver fatalities as a share of all road deaths rose 230% above 2009 levels in Colorado, according to the group. It says Washington recorded a similar pattern.
Meanwhile, the organisation has asked the Premier to meet its experts in testing, medicine and pharmacology. It is also calling for the government to publish the science behind the 50ng/ml threshold for public scrutiny.
