drug-driving-expert-panel-report

meta‐analysis has helped to negate these methodological weaknesses. The DRUID
report (2011), after taking age, and gender and confounding factors into account and
controlling for traffic conditions, estimated that the use of cannabis increased the risk of
serious or fatal injury in a motor vehicle accident by 1‐3 times. It was noted that
significant increased accident risk was apparent when the concentration of THC in the
blood was ≥5 µg/L, whether or not ingestion had occurred recently and regardless of the
origin of the drug (medicinal or illicit). For this reason and based on the evidence
(summarised above) available to the Panel, the threshold recommended in whole
blood for THC is 5 µg/L. At this concentration, the risks for involvement in, responsibility
for, or injury as the result of a traffic accident when driving under the influence of
cannabis are significant compared to a driver who has not consumed cannabis.
Cannabis and alcohol in relation to driving
The combined use of cannabis (as measured by THC) and alcohol produces severe
impairment of cognitive, psychomotor, and actual driving performance in experimental
studies and sharply increases the crash risk in epidemiological analyses (Ramaekers et
al, 2004). The risk estimate as an odds ratio (OR) for involvement in, or injury as the
result of a road traffic accident when driving under the influence of cannabis and
alcohol are shown below (Figure 4.1, adapted from Laumon, Gadegbeku, Martin, 2005).
Figure 4.1: Relationship between the odds ratio (OR) for the risk of a traffic accident
when cannabis and alcohol are detected alone and when alcohol and cannabis are
detected concurrently (adapted from Laumon, Gadegbeku& Martin, 2005).
THC + EtOH
Positive Sample
EtOH
THC
0.5 1 2 4 8 16 32
Odds Ratio (± 95% CI)
69