Drugs, driving and saliva

By Anna Sandiford 02/08/2010 2


After a brief airing on RadioLive this morning to talk about a recent press release regarding drug/drink driving statistics, I thought it pertinent to add a little something to clarify what I was saying (three minutes is not a long time to say what you need to say on an issue as big as this!).
Firstly, the press release relates to a report prepared by ESR using data gathered over a five year period. The data concerned 1046 drivers who died between 2004 and 2009 (89 per cent of dead drivers during that time). These individuals were tested for alcohol and drugs and nearly half (48 per cent or 500 drivers) tested positive. “Of those, 72 per cent or 365 drivers had either used cannabis, alcohol and cannabis, or a combination of drugs”, AA’s general manager for motoring affairs Mike Noon said.
The report showed that:
* 135 (27 per cent) had used alcohol alone;
* 96 (19 per cent) had used cannabis alone;
* 142 (28 per cent) had used both alcohol and cannabis; and
* 127 (25 per cent) had used a combination of drugs, which may have included alcohol and/or cannabis.

I haven’t seen the report but I would be interested to know what “tested positive” means. At what level is an individual deemed to have been “positive” for alcohol, i.e. did it include any level of alcohol or only levels in excess of the legal limit? Similarly with the drugs results, what counted as a “positive”? For the cannabis-positive individuals, was it the active ingredient, delta-9-tetrahydrocannabinol (THC), that counted as a positive or did it include people who had the inactive metabolites present? The difference being that THC is only present in the body for one to three hours after use of the drug whereas the inactive metabolites can be present for days or even weeks after the person was ‘stoned’. Incorrect interpretation of analytical results can be misleading to those who don’t realise there is a difference. How about the 25% who “had used a combination of drugs, which may have included alcohol and/or cannabis.” What does that mean?

Secondly, saliva testing at the roadside – does New Zealand need it and should the Police be provided with these tests? The tests being used in Queensland currently only detect cannabis, methamphetamine (auch as speed, P) and MDMA (in Ecstasy). So saliva tests are not the silver bullet in roadside testing at the moment. Blood still needs to be collected to detect the presence of other drugs such as benzodiazepnies and other common drugs of abuse such as the opiates, methadone and cocaine. There is information ‘out there’ about how to fake or con a saliva test – you can’t fake a blood sample or hair sample.

Thirdly, impairment tests, which are not a “pass” or “fail” – they are a subjective interpretation made by a police officer based on a set of criteria with which they have been provided and trained to dispense and observe. The new law that came into place at the end of last year saw the introduction of impairment testing at the roadside, a move which is at least ten years behind some other developed countries, but better late than never. This is a tool that the Police can now use to determine if someone is impaired, particularly if a breath screening test is negative. Individuals are required to undergo an impairment test if the Police Officer “has good cause to suspect the consumption of a drug” (Land Transport Amendment Bill (No. 4), Explanatory Note). Unsatisfactory completion of the impairment test could be the result of a number of issues, not just drugs (tiredness/fatigue, new prescription medication, undiagnosed medical condition, etc. – all of these I have encountered before in drink and drug driving cases). The way to solve the issue is to have a sample of blood from the driver analysed. The results and interpretations will be key in a successful criminal case. The law does allow for the defence of a valid prescription for a controlled drug.

The legislation that introduced impairment testing has a final point in the Explanatory Note that states blood specimens taken for alcohol offences can be analysed for research purposes to enable a better picture of drug-driving in New Zealand to be established. I assume this means that there will be a mass of data available pretty soon – and we can expect a new report on the effectiveness of impairment tests in reducing drug driving.


2 Responses to “Drugs, driving and saliva”

  • Well said Anna. When I first saw those statistics I spent about 10 min trying to get my head around it.

    It seems a bit like a “deception by confusion” job on behalf of the AA.

    If roadside cannabis testing does become routine, the testing must prove/correlate with impairment.

    My understanding is that there is no convenient biochemical test that can distinguish between ‘impairment’ and ‘having a toke at a party two days ago’. However I would be interested to know how this works in Queensland.

    With a justice system that punishes responsible people for a relatively harmless past time, false positives could be life wrecking.

  • Evan, does it really need to correlate to impairment- impairment is such a subjective standard, as has been long known with alcohol.

    Surely establishing the mere presence of THC/active metabolites should be enough. It would be interesting to known the sensitivity of saliva testing for THC levels- i.e. will minor passive exposure lead to ‘positive’ saliva tests.