The risk of being involved in a traffic accident rises with increasing blood alcohol level. Although it is known that certain medicines and intoxicants can affect the functions and skills needed in traffic and thus increase the accident risk, the correlation between the concentration of these substances in the blood and their impact level is less clear than for alcohol.
Zopiclone, a hypnotic, is the most commonly used sleep medication in Norway and is frequently detected in Norwegian drivers. A typical dose is 5 or 7.5 mg before bedtime. Previous research has shown an increased risk of traffic accidents during the first few days after a prescription for this medicine is dispensed.
Tested on healthy volunteers
In this study, researchers from the Norwegian Institute of Public Health compared the effect on traffic-relevant skills after taking zopiclone with similar effects on blood alcohol level. Sixteen healthy young male volunteers took part in the study on four days, where they randomly took a placebo, 5 mg zopiclone, 10 mg zopiclone or 50 grams of ethanol (giving up to 1 per mil) in a double blind study. They performed traffic-relevant / computerised tests before and up to 10 hours after receiving the study medicine.
Compared with blood alcohol levels
It takes a short time after taking a zopiclone tablet or drinking alcohol before the highest concentration of the active ingredient can be measured in the blood. After reaching a peak, the blood concentration gradually falls. The study showed that higher blood concentrations of both zopiclone and alcohol had a greater effect on the volunteers.
Significant effects were seen at concentrations in the blood equal to or greater than 16 micromoles per litre of zopiclone, and 0.25 ‰ of alcohol. These are low concentrations, and for zopiclone equivalent to expected blood levels about 5-15 hours after taking a normal dose of zopiclone.
The researchers also saw a certain degree of acute tolerance. The effects measured at certain blood drug concentrations within the first hour after ingestion were compared with the same blood drug concentrations measured at a longer time after ingestion. Clear differences in the effects were seen. The test subjects were significantly more affected shortly after intake than with the same concentration measured some time after ingestion.
The study confirms a number of similarities between alcohol exposure and effect after taking zopiclone.
Gustavsen I, Hjelmeland K, Bernard JP, Mørland J. Individual psychomotor impairment in relation to zopiclone and ethanol concentrations in blood – a randomized controlled double-blinded trial. Addiction (2011) Published online: DOI: 10.1111/j.1360-0443.2011.03693.x