• Acute tolerance;
  • ethanol;
  • impairment;
  • psychomotor performance;
  • randomized controlled trial;
  • zopiclone


Aims  To investigate individual traffic-relevant impairment related to measured blood zopiclone and ethanol concentrations. Also, we aimed to study possible development of acute tolerance.

Design  A randomized controlled four-way cross-over double-blind trial. Study drugs were zopiclone 5 or 10 mg, 50 g ethanol or placebo.

Setting  Laboratory study with computerized tests: Connor's Continuous Performance test, Choice Reaction Time and Stockings of Cambridge. Altogether, the tests consisted of 15 test components, representing three levels of behaviour (automotive, control, executive planning), relevant to traffic safety.

Participants  Sixteen healthy male volunteers.

Measurements  Each study day, 10 blood samples were collected from each volunteer. Fifteen psychomotor test components were registered at baseline and a further three times after intake. Impairment was defined as any individual deterioration in performance compared to individual baseline performance.

Findings  Blood drug concentrations up to 74 µg/l zopiclone and 0.100% ethanol were measured. We found a clear positive concentration–effect relationship for zopiclone and ethanol for both automotive and control behaviours, and a modest relationship for executive planning behaviour. Significant impairment started to be observed at concentrations above 16 µg/l zopiclone (automotive and control behaviour) and above 0.026% ethanol (automotive behaviour). Acute tolerance was found for both drugs.

Conclusions  The hypnotic, zopiclone, can impair psychomotor performance at blood concentrations as low as 16 µg/l.