While stimulants may improve unengaged workers’ performance, a new University of British Columbia study suggests that for
others, caffeine and amphetamines can have the opposite effect, causing workers
with higher motivation levels to slack off.
The study—published online by Nature’s Neuropsychopharmacology—explored
the impacts of stimulants on “slacker” rats and “worker” rats, and sheds
important light on why stimulants might affect people differently, a question
that has long been unclear. It also suggests that patients being treated with
stimulants for a range of illnesses may benefit from more personalized
“Every day, millions of people use stimulants to wake up, stay alert and
increase their productivity—from truckers driving all night to students
cramming for exams,” says Jay Hosking, a PhD candidate in UBC’s Department of
Psychology, who led the study. “These findings suggest that some
stimulants may actually have an opposite effect for people who naturally favor
the difficult tasks of life that come with greater rewards.”
Hosking says some individuals are more willing to concentrate and exert
effort to achieve their goals than others. However, little is known about the
brain mechanisms determining how much cognitive effort one will expend in
decision making for accomplishing tasks.
Hosking and study co-author Catharine Winstanley, a professor in UBC’s Department
of Psychology, found that rats—like humans—show varying levels of willingness
to expend high or low degrees of mental effort to obtain food rewards. When
presented with stimulants, the “slacker” rats that typically avoided challenges
worked significantly harder when given amphetamines, while “worker” rats that
typically embraced challenges were less motivated by caffeine or amphetamine.
While more research is needed to understand the brain mechanisms at work,
the study suggests that the amount of mental attention people devote to
achieving their goals may play a role in determining how stimulants drugs
affect them, Hosking says.
Winstanley, a Michael Smith Foundation for Health Research scholar, says
people with psychiatric illnesses, brain injuries, and attention deficit
hyperactivity disorder (ADHD) may benefit from treatment programs with greater
personalization, noting that patients often use stimulants to counter
drowsiness and fatigue from their conditions and treatments, with mixed
“This study suggests there may be important benefits to taking greater
account of baseline cognitive differences among individuals when considering
treatment programs,” says Winstanley, who is a member of the Brain Research
Centre at UBC and Vancouver Coastal Health.