How many cups of coffee you take a day at workplace? Well, a new study has found that caffeine, a substance found in coffee, tea and soft drinks, could turn hard workers into slackers. However, caffeine does not make lazy ones into productive superstars, found the study conducted on mice and appeared in the journal Neuropsychopharmacolory.

But stimulants like amphetamines appears to turn the less motivated ones into hard workers, although it fails to prevent hard workers from becoming slackers, Live Science reported.

In the study, team led by Jay Hosking at the University of British Columbia put 20 rats in boxes with two levers and five holes, one of which was to light up during the task.

By sticking its nose in that hole, the rat received a treat of sugar pellets. Using the levers, that’s could choose between a hard task, in which the hole lit up for a fifth of a second, about how low it takes to blink, and an easier one where the hole lit for a whole second.

If they completed the task successfully, the hard task, which required more brainpower, rewarded the rats with twice as many sugar pellets as did the easy task. These tasks study researcher, Jay Hosking said, – would be the equivalent of doing the bare minimum at work or going above and beyond in hopes of a promotion.

As in humans, some rats frequently choose the bare minimum task, and others went with the hard ones for the bigger pay off, Hosking said.

When the rats were given stimulants, either caffeine or amphetamines, they were more impulsive and responded quicker, but they were just as accurate at nosing the lit up hole. However, the two personalities of rat had opposite reactions when made to choose between tasks. On either of the drugs, the hard working rats became lazy, preferring the easy tasks in trials.

Meanwhile, when the lazy rats were given amphetamines, they became hard workers. Oddly, the same effect was not seen for the caffeine, Hosking said.