Kim Wolff: Drug driving limits

kim_wolffI am grateful to Jeremy Sare for his blog and the interest shown in the work of the expert panel on drug driving limits, but feel it is important to address some inaccuracies in his comments. The panel was required to consider drugs listed in the Misuse of Drugs Act (1971) and to make recommendations with regard to which controlled drugs should be specified in the subsequent drug driving regulations (Crime and Courts Bill), and to advise what an appropriate limit for each of those drugs might be. The focus on “psychoactive” drugs meant that the panel excluded the drugs in schedule 4 part 2 (anabolic steroids) from consideration. This is the first report to pull together in a critical manner the current scientific evidence concerning drug driving and road collision risk contextualised with data from English drivers.

To address some specific inaccuracies in Sare’s blog:  The final list of 14 drugs was based on careful evaluation of a wide range of material in addition to the prevalence data reported in the CSEW [1]. For instance, although the prevalence data for cocaine and mephedrone are similar, the evidence base for these drugs is significantly different. We found over 230 peer reviewed articles that had investigated cocaine and driving and no such publications for mephedrone. Consequently, we know a great deal about patterns of use concerning cocaine. Its acute effects and “come down” are well described in relation to the deleterious effects on driving behaviour. This is simply not the case for mephedrone, as yet.

Two papers have been published concerning mephedrone since the completion of the report: Crosbey et al, 2013, and Marinetti and Antonides (2013) [2,3]: the latter of who report that blood concentrations of synthetic cathinones do not appear to predict outcome regarding driving fatalities or impairment.

Secondly, crystal meth (methamphetamine) is actually well established as a recreational drug in this country. It has been identified in central London, from the analysis of anonymous pooled urine from portable urinals [4], and regionally using the sewage epidemiology approach to estimate community based drug consumption (from the River Avon and sewage effluent in Somerset to wastewater treatment plants in Yorkshire) (Bagnall et al, 2012; Kasprzyk-Hordern B, Baker DR, 2012 [5,6]). The panel was satisfied that methamphetamine is currently used across the UK and that there was sufficient evidence with regard to road safety risk to recommend thresholds.

Thirdly, the panel did not make threshold recommendations based on different drug classifications. This was clearly explained in the report. We looked specifically at risk: risk of an injurious or fatal road traffic collision (RTC) in drug drivers compared to non drug drivers.  Blood drug concentrations are themselves individually specific, a reflection of the physicochemical properties of the substance, pharmacokinetics, dosage, formulation, and route of administration. In our report the thresholds were exclusive to each drug and we took particular note of the concentrations observed in drug drivers.

The panel’s recommendations are for confirmatory tests to be undertaken in the police station and not in relation to road-side screening by type approved devices. This work is ongoing and is a separate vein of work.

A further point is that the confusion over the period of time that cannabis can be determined in the body relates to the identification of cannabis metabolites in urine. Our recommendation refers only to THC (delta-9-tetrahydro cannabinol or Δ9- tetrahydrocannabinol) the main psychoactive constituent of cannabis in blood. We have recommended a threshold above which it is considered that the risk to road safety is unacceptably high. The threshold is higher than average concentrations observed in those prescribed the drug.

It is important that the expert panel report is not seen as a fait accompli. The panel has endorsed the development of a five year drug driving strategy as recommended by the House of Commons’ Transport Committee (2010) in its inquiry into drink and drugs driving law. The panel has also suggested that any strategy should encompass an ongoing review of drug driving behaviours and any drug thresholds to be set.

Indeed, the new legislation is such that the “list” can be expanded as dictated by the scientific evidence as it becomes available. The popular drugs that Sare mentions (LSD, GBL, or psilocybin) were addressed in the panel report. We recommended keeping a watchful brief. To date, LSD, GBL, and psilocybin have not been detected in drivers apprehended for drug driving or involvement in road traffic collisions in this country.

We are really only at the beginning.

Kim Wolff, chair expert drug driving report, King’s College London.

I declare that that I have read and understood the BMJ Group policy on declaration of interests and I hereby declare that as chair of the drug driving panel I received an honorarium for this work and have no additional conflicting interests


1.    CSEW : Crime Survey for England and Wales
2.    Cosbey SH, Peters KL, Quinn A, Bentley A. Mephedrone (methylmethcathinone) in toxicology casework: a Northern Ireland perspective. J Anal Toxicol. 2013;37:74-82. doi: 10.1093/jat/bks094. Epub 2013 Jan 24.
3.    Marinetti LJ, Antonides HM. Analysis of synthetic cathinones commonly found in bath salts in human performance and postmortem toxicology: method development, drug distribution and interpretation of results. J Anal Toxicol. 2013;37:135-46. doi: 10.1093/jat/bks136. Epub 2013 Jan 29.
4.    Archer JR, Dargan PI, Hudson S, Wood DM.Analysis of anonymous pooled urine from portable urinals in central London confirms the significant use of novel psychoactive substances. QJM. 2013;106:147-52. doi: 10.1093/qjmed/hcs219. Epub 2012 Nov 22
5.    Bagnall JP, Evans SE, Wort MT, Lubben AT, Kasprzyk-Hordern B. Using chiral liquid chromatography quadrupole time-of-flight mass spectrometry for the analysis of pharmaceuticals and illicit drugs in surface and wastewater at the enantiomeric level.

  • NutmegJunkie

    Elvik’s meta‐analysis, a paper which you cite repeatedly, puts the odds ratio of injury/fatality whilst driving with cannabis in your system at 1.08 and 1.25 respectively (well within the range of legally tolerated risk for DUI alcohol). Can you explain why you ignored his best estimates on cannabis and driving but felt compelled to cite his figures in relation to every other drug?

  • Jeremy Sare

    I am also grateful to Dr Wolff for her comments. The conclusion of her response to my previous article was, “we are really only at the beginning.” I would wholeheartedly agree with that sentiment.

    In fact, the main thrust of the criticism in my previous article was the partial political presentation of the report’s findings rather than its overall scientific coherence. It is a comprehensive study by any standard, I should perhaps have made that more clear. Any anomalies I identified were to be set against the unwavering certainty of the Ministers who commissioned the report.

    However, I maintain the exclusion of mephedrone is an important omission from the list of drugs to be tested, given its rapid
    emergence among the 16-25 year olds in the last five years. The very contemporary use of the drug may pose problems with gathering report data for now. It does not seem conceivable that this drug taken on even moderate amounts would not impair driving ability. The ACMD identified that, “cathinones act as central nervous system stimulants” and there was a risk of “sympathomimetic toxicity.” Given its tendency to encourage repeat dosing and “bingeing”, I am sure few of us would say, had on heart, that mephedrone is not already significant drug of choice for the drug-driver.

    Just to clarify, neither was I suggesting crystal meth should be specifically excluded. Its prevalence is broadly restricted to
    small pockets of geography and demography such the gay dance scene in central London. The British Crime Survey barely registers its use level (0.1% 16-59 year olds in the last year), considerably less than magic mushrooms and LSD.

    Lastly, I realise the panel were not expected to take into account any individual drug’s classification. My point on ketamine being class C was in no way critical of the report’s conclusion but an aside which, “may say more about the illogicality of the classification system and less about the robustness of the report’s data.” After all, ketamine
    is now a lower classification than its substitute, methoxetamine (class B).

    The theme of several of my articles, particularly those published by the BMJ, are the misappropriation of good science for political expediency and regretfully it appears to be a theme which will continue with successive Governments.