Abstract

Alcohol is a drug known to impair the ability to drive safely and is acknowledged as a major factor in New Zealand road crashes [1]. However, the use of other impairing drugs by New Zealand drivers is largely unknown. This paper reports the prevalence of drug use by drivers killed on New Zealand roads. As this is a biased population sample the results can only indicate possible drug use in the wider driving population. Blood samples taken from 1046 deceased drivers were analysed for the presence of alcohol and a range of both illicit drugs and psychoactive medicinal drugs. Five hundred and forty-six (52%) of these drivers had not used alcohol or other potentially impairing drugs. Five hundred (48%) had alcohol and/or other drugs in their blood that may have impaired their ability to drive safely. Of these 500 drivers, 135 had used alcohol alone, 96 had used cannabis alone and 142 had used a combination of alcohol and cannabis, but no other drug. Alcohol concentrations in 351 drivers who had drunk alcohol ranged from 5 to 354 mg per 100 mL (mean 152 mg/100 mL). Levels of tetrahydrocannabinol (THC) in the blood of the 314 drivers who had used cannabis ranged from approximately 0.1 ng/mL to 44 ng/mL (mean 5.6 ng/mL). There were 127 drivers who had used some other combination of drugs, many still including alcohol and/or cannabis. Only 29 of the 500 drivers who had used a drug, had not used either cannabis or alcohol and 240 (48%) of the 500 drivers had used more than one potentially impairing drug.

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