OBJECTIVE: Driving under the influence of drugs is a major risk factor for road traffic collision deaths and injuries. We examined national trends in detection rates of cannabis, cocaine, amphetamines, methamphetamines, benzodiazepines, and opioids, alone and in combination, among drivers suspected of driving under the influence of an intoxicant (DUII) in Ireland 2012-2018.

METHODS: A repeated cross-sectional study design using immunoassay results from the Medical Bureau of Road Safety (MBRS). The MBRS is responsible for the chemical testing of intoxicants in all drivers arrested under the Road Traffic Acts 1968-2016 in Ireland. Detection rates for individual drugs, and combinations of drugs, per 1,000 drivers suspected of DUII were calculated. Negative binomial regression models (Adjusted Rate Ratios (ARR), 95% Confidence Intervals (CI)) were used to estimate age and gender adjusted time trends.

RESULTS: A total of 9,369 individuals were suspected of DUII during the study period (83% men). Annual increases in the detection of cocaine (ARR 1.21, 95% CI 1.18-1.24,  < 0.0001) and cannabis (ARR 1.13, 95% CI 1.09-1.17,  < 0.0001) were observed. Opioids, benzodiazepines, methamphetamines, and amphetamines saw minimal or no significant change over time. The co-detection of cocaine with cannabis (ARR 1.25, 95% CI 1.19-1.3,  < 0.0001), and cocaine with benzodiazepines (ARR 1.11, 95% CI 1.07-1.16,  < 0.0001) also increased.

CONCLUSIONS: Road safety is compromised by driving under the influence of drugs. The increasing detection of cocaine and cannabis, particularly among men, highlights the need for ongoing testing, and targeted interventions to reduce driving under the influence of these substances.