An accompanying editorial describes the research findings as "a cause for concern," not only in terms of the impact on drivers' health, but also because of the risk posed to road safety.
The researchers carried out a comprehensive review of published evidence on the use of mind altering substances among truck drivers by combing through international research databases.
They found 36 relevant studies, dating back to 2000, 28 of which had been carried out in countries with a large land mass, such as Australia, the US, and Brazil, and 23 of which obtained their information through survey data rather than biological samples.
The pooled data showed that the substances truckers used most frequently while on the road were alcohol, amphetamines ('speed'), cannabis, and cocaine. But the extent to which these were used varied widely, depending on the substance itself and the way in which the data had been collected.
So drinking on the job ranged from 0.1% to 91%, while the use of amphetamines ranged from 0.2% to 82.5%, cannabis from 0.2% to 30%, and cocaine from 0.1% to over 8%.
Prevalence was lower in studies relying on biological samples. But as the authors point out, these analyses only detect a substance that has been used hours or a few days beforehand, so tend to underestimate the true extent of use.
The prevalence of drinking on the job, for example, ranged from 10% (Pakistan) to 91% (Brazil), averaging out at 54%, for studies relying on survey data. But studies relying on biological samples suggested an average prevalence of 3.6%.
Twelve studies looked at the factors associated with the use of drugs on the job. The pooled data revealed certain common themes, among which were younger age; higher income; longer trips; night driving; alcohol consumption; fewer hours of rest; and pay below union recommended rates or that was linked to productivity."Psychoactive [mind altering] substances have been proved to impair driving and cause a greater risk of traffic accidents," write the authors. "Therefore gas stations, trucker stops and companies that employ these professionals must be more closely observed regarding the sale and consumption of these substances."
In a linked editorial, Professor Allard van der Beek, of the Institute for Health and Care Research at VU University, Amsterdam, The Netherlands, points out: "The results of this review are a cause for concern, not only for truck drivers using psychoactive substances, but also for the general public."
"It is beyond doubt" that alcohol and cannabis dull reaction times, he says, while amphetamines can stave off fatigue and boost concentration, but over the long term, continued use of high doses can be harmful to health.
Furthermore, other research shows that the use of stimulants prompts drivers to take more risks on the road and they are linked to an increased risk of falling asleep at the wheel and a subsequent road traffic collision, he says. Given the size and weight of trucks, this obviously increases the risks of serious injury and death.
Truckers use these substances to cope with long working hours and fatigue, he explains. But trying to change the culture will be hard. "Both road transport companies and truck drivers benefit financially from these long working hours," he writes.