An international review of studies looking at substance abuse by truckers finds those who are most likely to use alcohol or drugs on the job are younger and less well paid. Other risk factors for substance use include longer trips, night driving and fewer hours of rest.

The review included 36 studies conducted around the world, HealthDay reports. A majority of the studies relied on surveys of drivers instead of testing their biological samples. The most commonly used substances are alcohol, amphetamines, marijuana and cocaine, the review found.

“[Drugs and alcohol] have been proved to impair driving and cause a greater risk of traffic accidents,” the researchers wrote in the journal Occupational and Environmental Medicine. “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 commentary accompanying the study, Allard van der Beek of the Institute for Health and Care Research at VU University in Amsterdam noted, “The results of this review are a cause for concern, not only for truck drivers using psychoactive substances, but also for the general public.” He said alcohol and marijuana make it more difficult for truckers to react quickly, and amphetamines can cause long-term health problems.

Van der Beek said previous research has shown the use of stimulants prompts drivers to take more risks on the road. The drugs are linked with an increased risk of falling asleep at the wheel, and road traffic collisions.