Workplace accidents and injuries happen more often when people's physical abilities and judgement are impaired by drugs or alcohol. The workplace is not usually a place where research is conducted. There are many factors that make it difficult for an employer to measure the impact of a workplace drug testing program on the overarching goal of ensuring a safe workplace.
Some employers — particularly in sectors where safety is very important, such as the commercial driving and airline industries — choose to test workers randomly for drugs and alcohol (random drug and alcohol testing (RDAT)). Through such testing, employers hope to deter employees from inappropriate use of these substances. However, we do not know if RDAT produces the desired effect.
We wanted to know whether RDAT in the workplace prevents injuries and unplanned events that result in damage or loss of property (non-injury accidents) compared with no RDAT.
The evidence in this Cochrane Review is current to 1 November 2020.
We wanted to include all of the relevant research about RDAT in the workplace in our review. We looked for different kinds of published studies that measured how RDAT affected workplace safety. We excluded research on RDAT in commercial drivers, because another Cochrane Review covering these studies has already been published.
Two authors from our team examined all of the references identified by our search, but they found only one study that met our selection criteria and could be included in the review.
This study investigated random alcohol testing in airline employees in the USA whose jobs included safety-related tasks. The study did not test employees for drugs. Airlines are required by law to test and report on a randomly selected sample of their employees. The study used testing data from between 1995 and 2002. A total of 511,745 random alcohol tests were performed on airline employees.
From 1995 to 1997, random tests for alcohol included 25% of the relevant airlines' workforce each year. During this period, the average percentage of employees who tested positive for alcohol was 0.07%. From 1998 to 2002, the proportion of the workforce tested each year dropped to 10%. During this period, the average percentage of employees who tested positive for alcohol increased to 0.11%.
This means that when the airlines randomly tested a larger percentage of employees per year, a smaller proportion of them tested positive for alcohol. This relationship between the frequency of alcohol testing and the proportion of positive tests is what we would expect to see if testing has a deterrent effect, though one study alone cannot prove that there is a deterrent effect.
This study did not provide any information for other areas of interest to us, specifically:
- fatal injuries;
- non-fatal injuries (in which people are physically injured, but do not die);
- 'non-injury accidents'; that is, accidents in which people are not injured, but property, processes, materials, and/or the environment are damaged;
- absenteeism; and
- unwanted, or adverse, events associated with RDAT, including impacts on privacy, confidentiality and employee perceptions.
Quality of the evidence
Two of our team rated our confidence in the evidence, based on factors such as number of studies, study size and methods. Overall, our confidence in the evidence was very low. This means we cannot rely on what this study reported to make generalisations about the effectiveness of random alcohol testing alone, or random alcohol testing combined with drug testing (RDAT), in the workplace. We need researchers to do more studies to find the answers.
Study funding sources
The one study we included in our review was funded in part by two grants: a grant from the National Institute on Alcohol Abuse and Alcoholism, and a grant from the Centers for Disease Control and Prevention.
In the aviation industry in the USA, the only setting for which the eligible study reported data, there was a statistically significant increase in the rate of positive RAT results following a reduction in the percentage of workers tested, which we deem to be clinically relevant. This result suggests an inverse relationship between the proportion of positive test results and the rate of testing, which is consistent with a deterrent effect for testing. No data were reported on adverse effects related to RDAT.
We could not draw definitive conclusions regarding the effectiveness of RDAT for employees in safety-sensitive occupations (not including commercial driving), or with safety-sensitive job functions. We identified only one eligible study that reflected one industry in one country, was of non-randomised design, and tested only for alcohol, not for drugs or other substances. Our GRADE assessment resulted in a 'very low' rating for the quality of the evidence on the only outcome reported. The paucity of eligible research was a major limitation in our review, and additional studies evaluating the effect of RDAT on safety outcomes are needed.
Drug- and alcohol-related impairment in the workplace has been linked to an increased risk of injury for workers. Randomly testing populations of workers for these substances has become a practice in many jurisdictions, with the intention of reducing the risk of workplace incidents and accidents. Despite the proliferation of random drug and alcohol testing (RDAT), there is currently a lack of consensus about whether it is effective at preventing workplace injury, or improving other non-injury accident outcomes in the work place.
To assess the effectiveness of workplace RDAT to prevent injuries and improve non-injury accident outcomes (unplanned events that result in damage or loss of property) in workers compared with no workplace RDAT.
We conducted a systematic literature search to identify eligible published and unpublished studies. The date of the last search was 1 November 2020. We searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, Embase, two other databases, Google Scholar, and three trials registers. We also screened the reference lists of relevant publications known to us.
Study designs that were eligible for inclusion in our review included randomised controlled trials (RCTs), cluster-randomised trials (CRTs), interrupted time-series (ITS) studies, and controlled before-after (CBA) studies. Studies needed to evaluate the effectiveness of RDAT in preventing workplace injury or improving other non-injury workplace outcomes. We also considered unpublished data from clinical trial registries. We included employees working in all safety-sensitive occupations, except for commercial drivers, who are the subject of another Cochrane Review.
Independently, two review authors used a data collection form to extract relevant characteristics from the included study. They then analysed a line graph included in the study of the prevalence rate of alcohol violations per year. Independently, the review authors completed a GRADE assessment, as a means of rating the quality of the evidence.
Although our searching originally identified 4198 unique hits, only one study was eligible for inclusion in this review. This was an ITS study that measured the effect of random alcohol testing (RAT) on the test positivity rate of employees of major airlines in the USA from 1995 to 2002. The study included data from 511,745 random alcohol tests, and reported no information about testing for other substances. The rate of positive results was the only outcome of interest reported by the study.
The average rate of positive results found by RAT increased from 0.07% to 0.11% when the minimum percentage of workers who underwent RAT annually was reduced from 25% to 10%. Our analyses found this change to be a statistically significant increase (estimated change in level, where the level reflects the average percentage points of positive tests = 0.040, 95% confidence interval 0.005 to 0.075; P = 0.031). Our GRADE assessment, for the observed effect of lower minimum testing percentages associating with a higher rate of positive test results, found the quality of the evidence to be 'very low' across the five GRADE domains. The one included study did not address the following outcomes of interest: fatal injuries; non-fatal injuries; non-injury accidents; absenteeism; and adverse effects associated with RDAT.