A two page note published in 1965 in the British Journal of Addiction commented on information issued by the British Medical Association about the difficult issue of ‘drink driving’. In the UK in 1960 it had become an offence to drive, attempt to drive or be in charge of a motor vehicle on a road or other public place while “unfit to drive through drink or drugs”. However, technical problems made determining the threshold for this offence problematic, and a technical committee of the BMA had concluded in 1960 that “clinical examination in the absence of chemical tests is neither sufficiently sensitive nor reliable enough to detect deterioration in driving performance. . .”. This paper examined further disadvantages of clinical examination as a method of detecting impairment of driving ability, and recommended that once a blood alcohol concentration of 80 mg/100 ml had been reached the offence should be regarded as proved despite the fact that a doctor may have been unable to detect impairment of driving. A legal drink driving limit was eventually set in 1967.
This debate has echoes in the present, where psychoactive substance use and driving is now the subject of interest. Driving while under the influence of drugs is an offence under the Road Traffic Act 1988 with penalties similar to those for driving while under the influence of alcohol. However, a new offence of driving over a prescribed drug limit was introduced in England and Wales in March 2015. This results from the North report (2010) and largely from many of the recommendations of an expert panel on drug driving and safety.
The new offence specifies 16 controlled drugs, and specifies the limit in blood for each of the drugs. Broadly it deals with two groups: illicit (cocaine, THC, ketamine, LSD, methylamphetamine, MDMA, heroin metabolite, 9-MAM and benzoylecgonine) with low (zero tolerance) blood thresholds and the second group which consist mainly of licensed prescriptions only medicines that have a liability to be abused (amphetamine, clonazepam, morphine, diazepam, oxazepam, methadone, lorazepam, temazepam, flunitrazepam. For this second group, the blood thresholds are higher than a zero tolerance. The blood threshold levels were based on road safety and risk of serious or fatal accidents. These confirmatory blood tests detailed in the legislation are taken at the police station. Mobile testing equipment has been approved to detect cannabis (THC) and cocaine. There is further development of mobile road-side drug screening devices at present.
Concerns have been expressed about thresholds level and the use of prescriptions for pain and over the counter codeine. The limits are generally above the usual therapeutic dose range so most would be unlikely to be driving with a level above the specified level. For those on particularly high doses, are taking medicines in accordance with instructions and who might be above the threshold level, they may raise the statutory ‘medical defence’. Guidance has been given to all doctors on this new driving offence and the role of the statutory medical defence. Patients are asked to have some evidence available if required but noted that care needs to be taken about issues of confidentiality with this evidence. However, it remains an offence to drive with any use of drugs prescribed or not if impaired. The current medical standards on driving are available on the DVLA web site.
The opinions expressed in this commentary reflect the views of the author(s) and do not necessarily represent the opinions or official positions of the Society for the Study of Addiction.