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Impairment due to amphetamines and benzodiazepines, alone and in combination
Gudrun Høiseth1, Hilde Andås2, Liliana Bachs2
1Norwegian Institute of Public Health, Division of Forensic Sciences, Oslo, Norway; Center for Psychopharmacology, Diakonhjemmet Hospital, Oslo, Norway.
Introduction:
The impairing effects of combined use of amphetamines and benzodiazepines among recreational drug users are not well described, but knowledge about this is important in the risk assessment of such combined drug use. The aim of this study was to compare the impairment, among apprehended drivers, as judged by a clinical test of impairment (CTI), in cases where a combination of amphetamines and benzodiazepines was detected, in blood, with cases where only one of the two drug groups was detected.
Methods:
The results of CTI judgments were compared to toxicological drug tests of blood samples that were obtained at the time of CTI screening in cases containing amphetamines only, cases containing different benzodiazepines only, and cases containing a combination of amphetamines and benzodiazepines.
Results:
There were significantly more drivers being judged as impaired in the combined group (n = 777), compared both with amphetamines alone (n = 267, χ(2) = 47.8, p < 0.001) and benzodiazepines alone (n = 153, χ(2) = 7.0, p = 0.008). This was also seen when only including the lowest concentrations of benzodiazepines (χ(2) = 4.3, p = 0.038). The concentrations of the drugs were higher in the single drug groups, compared with the combined group.
Conclusion:
This study indicates that during real-life driving, those influenced by both amphetamines and benzodiazepines are more impaired, as judged by the CTI, compared with those influenced by either drug alone, although the combined group showed lower drug concentrations.