Abstract: We included two interrupted time-series studies conducted in the USA. One study was conducted in five large US transportation companies (N = 115,019) that carried passengers and/or cargo. Monthly injury rates were available from 1983 to 1999. In the study company, two interventions of interest were evaluated: mandatory random drug testing and mandatory random and for-cause alcohol testing programmes. The third study focused only on mandatory random drug testing and was conducted on federal injury data that covered all truck drivers of interstate carriers. We recalculated the results from raw data provided by the study authors. Following reanalysis, we found that in one study mandatory random and for-cause alcohol testing was associated with a significant decrease in the level of injuries immediately following the intervention (-1.25 injuries/100 person years, 95% CI -2.29 to -0.21) but did not significantly affect the existing long-term downward trend (-0.28 injuries/100 person years/year, 95% CI -0.78 to 0.21). Mandatory random drug testing was significantly associated with an immediate change in injury level following the intervention (1.26 injuries/100 person years, 95% CI 0.36 to 2.16) in one study, and in the second study there was no significant effect (-1.36/injuries/100 person years, 95% CI -1.69 to 0.41). In the long term, random drug testing was associated with a significant increase in the downward trend (-0.19 injuries/100 person years/year, 95% CI -0.30 to -0.07) in one study, the other study was also associated with a significant improvement in the long-term downward trend (-0.83 fatal accidents/100 million vehicle miles/year, 95% CI -1.08 to -0.58). There is insufficient evidence to advise for or against the use of drug and alcohol testing of occupational drivers for preventing injuries as a sole, effective, long-term solution in the context of workplace culture, peer interaction and other local factors. Cluster-randomised trials are needed to better address the effects of interventions for injury prevention in this occupational setting.

Plain-language summary: We conducted a systematic search of the literature on the effects of alcohol and drug screening among occupational drivers for preventing injury. We then appraised the quality of the studies found and assessed their results. We found two time-series studies conducted in the USA. One was conducted in five large transportation companies, and it examined the effects of two interventions of interest: implementation of legislation for mandatory random drug testing and mandatory random and for-cause alcohol testing. The other study was conducted using national injury data. There is limited evidence that in the long term mandatory drug-testing interventions can be more effective than no intervention in reducing injuries in occupational drivers. For mandatory alcohol testing there was evidence of an immediate effect only. Given the widespread practice of alcohol and drug testing and the paucity of evaluation studies found, more evaluation studies are needed. Interrupted time-series is a feasible study design for evaluating interventions that aim at preventing alcohol and drug related injuries. However, time-series studies of higher quality and of long duration are needed to increase the level of evidence. A cluster-randomised trial would be the ideal study design to evaluate the effects of interventions for injury prevention in this occupational setting.