Researchers found alcohol exacerbated impairment throughout sleep loss; cannabis did not significantly further degrade reaction time but did degrade driving performance.
Researchers at Washington State University, in collaboration with Pulsar Informatics and the National Safety Council, developed a research protocol to conduct an in-laboratory pilot study of three known causes of impaired alertness – fatigue, alcohol and cannabis – using objective and self-reported measures.
In safety sensitive environments, it is a fundamental safety requirement that workers be reliably alert. Some organizations require designated individuals to undergo periodic fitness for work evaluations that include an assessment of alertness, which can be impaired by any number of factors including fatigue, medical conditions, alcohol, prescription medications and recreational drug use, among other reasons.
Regardless of whether the requirement is based on a regulation, industry guidance or company policy, it is sensible that if an operational task requires a worker to be reliably alert, then there should be a formal process and an objective framework for the evaluation of potential impairment.
There is a critical need for a such a framework. In practical terms, organizations need to create fitness for work policies and provide guidance on safe practices in occupational settings. Robust data is needed to aid in the interpretation of alertness impairment measures and to develop a relationship matrix relative to the various causal factors.
Six healthy individuals (ages 23 to 37, all male) completed two 24-hour, in-laboratory study visits separated by one week. During each visit, study participants were kept awake for 15 hours (from 3 p.m. to 6 a.m. the next day) and completed a series of tasks every two to three hours, which included evaluating:
For the second visit, participants completed the same procedures as in the first visit but were randomized to receive an oral cannabis or alcohol dosage late in the evening.
Performance on a sustained attention task worsened through the second half of the extended waking period (after midnight), with slower reaction time, lapses of attention and more false starts. Alcohol increased reaction time and lapses but did not significantly affect false starts. Cannabis did not significantly affect reaction time, lapses or false starts.
Performance on the driving simulator also worsened after midnight. Lane deviation increased, and mean braking latency decreased. Cannabis significantly increased mean lane deviation but not time between braking. Alcohol did not significantly affect mean lane deviation or mean braking latency above and beyond the impact of sleep deprivation alone.
Subjective ratings of sleepiness significantly increased after midnight, with some evidence indicating lower sleepiness ratings in those administered cannabis as compared to alcohol. Physical symptoms following driving simulation increased after midnight but were not further impacted by cannabis or alcohol.
Importantly, researchers did not attempt to make the alcohol and cannabis doses similar in potency; therefore, these results should not be interpreted as providing any indication of the relative impairment impact or safety profile. Yet, our findings provide preliminary evidence suggesting that commonly used drugs such as alcohol may amplify impairment from sleep loss, which may have critical implications for the operation of vehicles and other safety-sensitive activities.
Full study findings will be released in the coming months. These findings will aid future interpretation of alertness impairment data and advance progress by providing an objective framework by which to safely measure impairment and guide fitness for work policy and practice in occupational settings.
For more information on impairment as a safety risk, visit nsc.org/impairment.
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