The use of prescription medication and other drugs by New Zealand drivers with illegal blood alcohol levels.

Objective: This study examined the prevalence of the use of prescription medicines and other drugs by a selected subgroup of New Zealand drivers. The use of potentially impairing prescription drugs by the driving population is largely unknown. The population studied was drivers who were stopped by police, failed a breath alcohol test, elected to provide a blood sample for laboratory analysis, and had blood alcohol levels exceeding the legal limit.

Method: Blood samples taken from 3,050 drivers during the period 2011 to 2015 were analyzed for the presence of alcohol (ethanol) and a range of both prescription and illicit drugs using liquid chromatography with time-of-flight mass spectrometric detection (LC-TOFMS) and an immunoassay screen for cannabis use.

Results: One thousand two hundred thirty-five of these drivers had used alcohol in combination with potentially impairing drugs (41%) and alcohol only was detected in 1,815 of the samples (59%). Five hundred of the drivers had used prescription medication (16%), 816 had used cannabis (27%), and 81drivers had used other illicit recreational drugs (2.7%), all in combination with alcohol. The top 7 prescription medicines used in combination with alcohol were citalopram, fluoxetine, and venlafaxine (antidepressants); quetiapine (antipsychotic); diazepam (sedative); and tramadol (opioid).

Conclusions: Drug use did not correlate with the amount of alcohol consumed, and the use of multiple drugs in combination with alcohol was prevalent. Although this is a biased population sample, the results indicate the possible use of impairing prescription medication in the wider driving population and the need for more awareness of the potential impairment by all types of prescription medication.