What Do the Researchers Say?
A Sydney Trains Study, published in the Journal of Analytical Toxicology, 2016;40;479-485 (and the Australian National Library of Medicine) reports that in 1,500 paired urine and oral fluid tests, substances were detected in 3.7% of urine samples and 0.5% of oral fluid samples. Why the difference? Christie and Lewis state on page 11 (5) that the detection of cannabis by Oral testing is difficult, in fact unreliable.
What differences exist between the two testing methodologies? OFT has a shorter window of detection, hours, compared to urine screening, which can detect use after several days. OFT is therefore seen to align more closely with the very recent use of drugs (intoxication), but not detect drug use during the withdrawal (hangover) stage when safety risks are high to severe. See the table on p. 6 of Christie and Lewis that shows the impairment risks during the time stages of drug use:
Risk during intoxication
with low to moderate dose
|Risk during intoxication||Hangover risk||
Ongoing risk is chronic /
|Cannabis||Moderate||Moderate to high||low||Moderate|
|Low||Moderate to high||High to severe||High to severe|
|Opioids||Moderate to high||Severe||Low to moderate||High to severe|
|Sedative||High to severe||Severe||Moderate to high||High to severe|
On p. 13 Christie and Lewis comment that OFT has serious shortcomings with a high likelihood of failure to detect use. This statement is borne out in the data recorded by Victoria and Queensland Police from random screenings (see p. 15) where OFT detected Methamphetamine but not cannabis use in drivers, whereas research shows that cannabis (THC) is most commonly the drug used by drivers.
They further add: This confirms that oral screening for cannabis is very insensitive to THC.
In view of this research, PF Olsen is reluctant to rely on OFT for two important reasons: (1) Detecting recent use (particularly of our most prevalent drug Cannabis/THC) using OFT could be unreliable; and (2) OFT cannot detect drug use during the hangover stages when safety risks are significant!
View this article in Safety Bulletin 124