Please find below the summary of a report commissioned by the Department for Transport (DfT) on driving under the influence of drugs.
The full report can be found at:
Although this report was commissioned by the Department for Transport (DfT), the
findings and recommendations are those of the authors and do not necessarily
represent the views of the DfT. The information or guidance in this document (including
third party information, products and services), is provided by DfT on an ‘as is’ basis,
without any representation or endorsement made and without warranty of any kind
whether express or implied.
The expert Panel on drug driving was asked by the Department for Transport in April 2012 to make recommendations about which drugs should be included in regulations for the purposes of a new offence of driving with a specified controlled drug in the body. It was also asked to consider what thresholds for these drugs should be set in regulations to improve road safety. The extent of the road safety problem associated with drug driving was recently presented in the 2010 North report.
The House of Commons Transport Select Committee (2010) published a report on its inquiry into drink and drugs driving law. The committee recommended that the Government develop a five‐year strategy for tackling drug‐driving and the Panel endorsed the development of a strategy which should also encompass the review of drugs for which thresholds might be set in forthcoming legislation. In its report the expert Panel has considered the scientific evidence related to drug driving in the UK: the prevalence of drug use amongst drivers, the prevalence among road traffic accident drivers and the risk to road safety and other factors that might influence the problem. The Panel has considered how different drugs affect drivers in the general population and in particular the risk of a road traffic accident whilst driving under the influence of these substances. The findings of epidemiological and experimental studies formed a large part of the Panel’s discussion about threshold concentration limit in blood. To justify a limit, risk estimates (calculated as odds ratios) were considered alongside the known pharmacokinetics and pharmacodynamics of the drugs.
Contextual data on the concentrations of drugs in drivers apprehended in the UK for suspected and witnessed impairment or when involved in a RTA was also available to the Panel. In most cases, the Panel’s recommendations are restricted to the parent drugs and/or active metabolites: so that the presence of a drug above the cut‐off concentration generally means that the person will be unfit to drive. However, in some cases, it is necessary to focus on the metabolite, e.g. when the parent drug is unstable and is metabolised very rapidly, e.g. heroin has a half‐life of 3 – 6 minutes and its active metabolite 6‐acetylmorphine also has a short half‐life and is unstable in blood. In that case, morphine is used, but it is also pharmacologically active. Cocaine is also unstable in blood even when preserved with fluoride, and in this case a threshold for the inactive metabolite benzoylecgonine is suggested in addition to the threshold in cocaine. The medicinal drugs were a particularly challenging issue. Characterisation of these drugs for drug‐driving purposes is conceptually difficult because several different user groups, who use the medication in different circumstances, are involved, including those who legitimately use licensed psychoactive medication; those prescribed psychoactive medication for treatment of drug/alcohol dependence and; those who obtain prescribed psychoactive medication illicitly and use it alone or with other drugs for recreational purposes.
When considering thresholds, the Panel looked for clear scientific evidence of risk estimates (expressed as odds ratios) for RTAs. This has included using epidemiological evidence and meta‐analysis to assess road safety risk. The Panel has also considered the issue of patients becoming tolerant to psychoactive medication when on long‐term stable doses. However, in some cases, for example with regards to benzodiazepines, there is scientific evidence that even compliant patients prescribed benzodiazepine drugs are at increased risk of an RTA when compared to drivers who are not under the influence of these drugs. Risk is especially high during the first 4 weeks of treatment and is particularly increased when medicines are consumed in combination with alcohol. It is important to recognise this and take steps to reduce this risk. The effects of the ‘Z‐drugs’, so called because they are a group of hypnotic agents which each begins with ‘Z’ and are used solely in the treatment of insomnia, were also explored by the Panel. Zaleplon was found to be infrequently prescribed and so epidemiological data are limited. The Panel were satisfied that the drug has not been linked to an increased risk of RTA in the scientific literature. On the other hand there is some indication that zolpidem may affect driving behaviour particularly during the first 4 weeks of use and this drug should be kept on the radar for future recommendations. Zopiclone however is a cause for concern. Although not controlled under the Misuse of Drugs Act (1971) and thus outside of the Panel’s remit, zopiclone has been reported to have a high RTA risk in epidemiological studies and a meta‐analysis reported increased risk estimates (as an odds ratio) for fatal injury (OR: 2.6) and injury (OR:1.6) for zopiclone. The Panel believes that there is sufficient evidence to suggest a need for a threshold to be set for zopiclone as a road safety measure.
In considering what thresholds should be set for common prescription medication, the Panel has looked at the blood concentrations found in those using doses of the drug within a normal therapeutic range used in prescriptions compared to concentrations found in addicts misusing medicines. Where there is a lack of consensus with regard to blood concentrations that pose a risk to driver safety the Panel also looked at concentrations of blood measured in individuals suspected and known to have been driving under the influence of drugs. In relation to morphine, for example, the Panel has recommended a limit which is significantly above the average steady‐state concentrations of morphine in blood found in cancer patients prescribed morphinelong term doses. The Panel noted that there had been a considerable increase in poly‐drug use by drivers and the road safety risk associated with driving after consuming drugs and alcohol at one time is extremely high. Based on this evidence, the Panel is also recommending that a lower limit should be set for certain drugs where they are found in combination with alcohol, as this combination leads to much greater accident risk when driving than a low concentration of the drug on its own. These lower drug limits are recommended when blood alcohol concentrations above 20 milligram per 100 millilitres (20 mg/100ml) of blood is also detected. The Panel are aware of the fact that there are drugs with similar pharmacological mechanisms of action to those discussed in this report and which, by analogy, are likely to pose similar impairing effects on driving performance. These drugs include the so‐ called ‘legal highs’ designed to mimic the effects of illicit drugs but sufficiently different in chemical structure to (initially) avoid being controlled under the Misuse of Drugs Act. The prevalence of ‘legal highs’ among drivers or the effects of newer ‘designer drugs’ on road safety remains unknown and because of their current relatively low usage in the UK, there is often incomplete knowledge of their pharmacokinetics and, especially, insufficient evidence regarding their possible involvement in RTAs. To date odds ratios (ORs) for road traffic accident risk have not been estimated for these compounds. The Panel was unable to establish threshold limits for some newly controlled drugs such as mephedrone. The Panel strongly endorses the North Report (2010) recommendation that laboratories undertaking forensic work should be encouraged to screen routinely for a wider range of psychoactive substances so as to establish a more accurate picture of the type of substances prevalent in those suspected of driving under the influence of drugs.