New research from RCSI University of Medicine and Health Sciences and the Medical Bureau of Road Safety based in University College Dublin has revealed a dramatic increase in the detection of cocaine and cannabis among Irish drivers suspected of driving under the influence, pointing to changing patterns of drug use on Irish roads.

The two studies, published in Traffic Injury Prevention and Drug and Alcohol Review, represent the first national analysis of trends in drug detected among suspected drug-impaired drivers in Ireland and provide critical evidence to inform future road safety interventions.

The research team, led by Professor Gráinne Cousins from the RCSI School of Pharmacy and Biomolecular Sciences, analysed toxicology data collected by the Medical Bureau of Road Safety (MBRS) between 2012 and 2020. Their findings show a significant and consistent increase in cocaine detections over time, with cocaine overtaking benzodiazepines by 2018 to become the second most commonly detected drug after cannabis.

Over the same period, cannabis detections continued to rise year on year, cementing its position as the most frequently found drug among drivers suspected of drug driving.

Between 2012 and 2018, blood and urine samples from more than 9,000 drivers underwent toxicological analysis by the MBRS. 83% of those tested were men. Cannabis was detected in almost half of all cases, while benzodiazepines were found in around one in four drivers.

Cocaine was detected in 16.5% of cases across the years studied; however, the researchers observed a striking 21% year-on-year increase in cocaine detection. Cannabis detections rose by 13% annually. These trends signal a change in the drugs most commonly used by people driving under the influence in Ireland.

The researchers also analysed data from 2019 to 2020 in more detail, when 4,856 samples tested positive for at least one drug. By applying a statistical method called latent class analysis, they were able to group drivers into six distinct categories based on the drugs found in their system.

Younger men were more likely to fall into groups where only cannabis was detected, or where cannabis and cocaine were used together. In contrast, older drivers, including a higher proportion of women, were more often found in groups involving multiple drugs or opioid use. More than 40% of all samples contained more than one drug, showing that drug use among drivers is often complex and varied.

The research has significant implications for road safety enforcement and public health policy. By identifying both the drugs most commonly detected and the profiles of those driving under their influence, the findings can support the development of tailored education, deterrence, and harm reduction strategies that respond to real-world trends on Irish roads.

Dr Louise Durand, lead author of the study, said: “This research shows not only a significant rise in cocaine and cannabis detections but also that people driving after using drugs are not a homogenous group. Understanding these patterns is crucial for shaping more effective, targeted prevention, enforcement and public health strategies.”

Professor Denis Cusack, Director of the Medical Bureau of Road Safety, said: “Driving under the influence of drugs is a major risk factor for serious and fatal road traffic collisions. The data clearly illustrate changing patterns of drug use on Irish roads. These findings will help inform more focused interventions, including medical support and rehabilitation for certain categories of drivers, that aim to reduce harm and improve road safety for everyone.”

The studies were carried out in collaboration with the Medical Bureau of Road Safety and the HSE National Social Inclusion Office, with funding from the Health Research Board under its Secondary Data Analysis Programme.

The papers, Drug and polydrug detection in drivers suspected of driving under the influence of an intoxicant in Ireland 2012-2018: a national repeated cross-sectional study, published in Traffic Injury Prevention and Patterns of drug and polydrug detection in drivers suspected of driving under the influence of an intoxicant in Ireland 2019-2020: A latent class analysis, published in Drug and Alcohol Review, present the findings in full.