Only "lazy" people will get a jolt from coffee, says a shocking new study the stuff actually turns motivated go-getters into slackers. The research at the University of British Columbia's Department of Psychology discovered that stimulants, including caffeine and amphetamines, do not raise motivation levels. For the paper published in Nature's Neuropsychopharmacology, scientist found that coffee made "busy" rats less active, and turned "lazy" ones into energetic ones. When given stimulants, the "slacker" rats that typically avoided challenges worked significantly harder, while "worker" rats that usually embraced challenges were less motivated after having caffeine or amphetamines. "Every day, millions of people use stimulants to wake up, stay alert and increase productivity from truckers driving all night to students cramming for exams," says study leader Jay Hosking. "These findings suggest that some stimulants have an opposite effect for people who naturally favor the difficult tasks of life that come with greater rewards."