Eighty participants underwent six experimental conditions that involved the consumption of cigarettes containing either no THC (placebo), 1.8 per cent THC and 3 per cent THC, together with the consumption of alcohol to reach blook alcohol concentrations of either 0 per cent (placebo), 0.03 per cent or 0.05 per cent. Participants then performed a driving simulation task and undertook the Standard Field Sobriety Tests. This research confirmed that the consumption of cannabis, with or without alcohol, significantly impairs driving behaviour.
This research summary by Roger Nicholas provides a plain English summary and implications for police for An evaluation of the Standardised Field Sobriety Tests for the detection of impairment associated with cannabis with and without alcohol (NDLERF monograph no. 17).