In 2008, injured drivers who were admitted to the emergency unit at Oslo University Hospital, Ullevaal were invited to participate in a study about drugs and accident risk. 96 injured drivers took part. They were compared with more than 5,000 drivers in normal traffic who were randomly stopped in eastern Norway as part of a roadside study.
All the drivers were tested for alcohol, illegal drugs and medicines such as hypnotics and sedatives. The researchers obtained results from blood samples from the injured drivers, while saliva samples were taken from the "roadside-drivers."
The psychoactive medicines included also hypnotics and sedatives such as Zopiclone, Valium, Vival and Stesolid.
One in five injured had substances in the blood
It is well known that alcohol represents a traffic risk. This study shows that alcohol is not the only problem; many injured drivers had used medicines or illegal drugs, sometimes together with alcohol. Few of the drivers in the normal traffic group had alcohol or other substances in the blood.
- One in five injured drivers had one or more substances in the blood. Most common were alcohol, stimulants such as cocaine and amphetamines, and hypnotics / sedatives of the benzodiazepine type, such as Valium, Vival and Stesolid.
- 3 out of 100 drivers in normal traffic had medicines or illegal drugs in the blood; this was mainly the hypnotic zopiclone (e.g. Imovane), a benzodiazepine-type sedative or cannabis. Only three out of 1000 had alcohol in their blood.
Combinations are dangerous
The researchers calculated the risk of being injured when driving with alcohol, drugs and other psychoactive drugs in the blood. They found that:
- The risk of injury was greatest when the driver combined alcohol with another substance, whether illegal drug, hypnotic or sedative. The calculation shows that the risk increased over 200-fold compared with the risk for drivers who had nothing in their blood.
- The risk of injury was also significantly increased if the driver
- had only drunk alcohol
- had taken a combination of three or more substances
In the comparison between the two driver groups, their gender and age, day of the week and season were taken into account. Saliva samples reflect the substances present in blood, and cut-off values corresponding to equivalent blood values were used. In all, 30 substances that impair driving skills were monitored.
The findings from this study point in the same direction as a previous study on deceased drivers. They both show that it is particularly dangerous to combine alcohol with other substances, and that alcohol alone or combinations of substances, for example multiple medicines, medicines and illegal drugs, also present a significant risk factor in traffic.
Information on the use of alcohol and medicines while driving is important
- Some of the medicines detected in the injured drivers were prescribed by general practitioners. Do patients get enough information?
“It is certainly vital that patients are given information about the risks of driving if they use multiple substances simultaneously, for example, combining a sleeping pill with alcohol. But sedatives and hypnotics can also be purchased illicitly” says Stig Tore Bogstrand, a researcher and nurse at Oslo University Hospital, Ullevaal. Bogstrand is the first author on the study which is now presented in the BMC Public Health journal.
- You have found that combination increases the risk significantly. Are high values required before the accident risk increases?
“We have not considered the blood concentrations of the drugs, only if they are present in levels over the threshold limits. Other studies show, for example, that combining a low dose of alcohol with a low dose of cannabis impairs driving skills considerably, whilst driving skills would be less affected if one only had a low dose of either substance. Other studies have also shown that driving skills are impaired more with a higher amount of alcohol or other substances in the blood.”
- How dangerous is it to have just one medicine or illegal substance in the blood?
“Among the injured drivers concerned this is a small number. We can therefore not make accurate assessments on this. But it is clear that alcohol presents a much bigger risk than the use of one medicine in low therapeutic doses – that is, as prescribed or recommended by a doctor. With regards to illegal drugs, amphetamine presents the greatest risk.”
- What is the significance of this study?
“We believe that the results can draw attention to how both illegal drugs and medicines are a frequent contributing cause of traffic injuries. The roadside studies show that in Norway few drive with blood alcohol above the permitted blood alcohol levels. The biggest traffic risk is represented by those who take the chance to drive when they combine alcohol and other substances,” says Per Trygve Normann, Chief Scientist at the Division of Forensic Medicine and Drug Abuse Research at the Norwegian Institute of Public Health.
Stig Tore Bogstrand, Hallvard Gjerde, Per Trygve Normann, Ingeborg Rossow and Øivind Ekeberg:
Alcohol, psychoactive substances and non-fatal road traffic accidents - a case-control study. BMC Public Health 2012, 12:734.