A new study from the Norwegian Institute of Public Health shows a positive link between the amount of the hypnotic (sleeping medicine) zopiclone in the blood and the chance of being assessed as impaired in a clinical examination.
The study also included drivers who only showed alcohol in their blood test.
"This could be important background knowledge in the discussion about establishing legal limits in traffic for sedatives or sleep-inducing medicines as we have for alcohol", says Ingebj©ªrg Gustavsen from the Division for Forensic Toxicology and Drug Research.
Common sleeping medicines
Hypnotics that contain zopiclone and zolpidem (e.g. Imovane and Stilnoct) are widely used throughout the world and it is reported that between 3 and 7 % of the adult population uses these drugs. Researchers at the Norwegian Institute of Public Health have now studied if there is a link between the concentration of zopiclone or zolpidem in the blood and being assessed as impaired during a clinical examination. The study was done on anonymised material by comparing blood samples and results from clinical tests for the period January 2000 to December 2007. The same study was performed on another group of drivers who only had alcohol in the blood.
Link between substance concentration and impairment
The proportion of drivers who were evaluated as impaired increased with zopiclone-concentration in the blood. A similar positive link was not found for zolpidem. For alcohol, as expected, there was a significant link between the proportion of impaired drivers and alcohol concentration in the blood.
"We know that the clinical examination performed on suspicion of driving under the influence is a test that is most sensitive for alcohol impairment, and less sensitive for other substances. Other types of impairment are therefore not necessarily picked up with this study, which can explain why we have not found positive links for zolpidem. Another reason can be that there were few drivers in our sample, particularly in the groups with low concentrations," says Gustavsen.