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The new study conducted by researchers from University of British Columbia in Canada suggests marijuana use could lead to laziness after they found an active compound in marijuana (tetrahydrocannabinol) which made rats less willing to attempt a challenging task.
The lead study author Mason Silveira, of the Department of Psychology at Columbia, and colleagues noted that previous studies have suggested the activation of cannabinoid receptors can affect decision-making related to physical effort, making an individual physically lazy.
About 29 male rats were trained by the researchers to complete a behavioral experiment, which involves them deciding whether they wanted to complete an easy or difficult cognitive task in order to receive a reward.
The easy task required the rats to react to a light that flashed for 1 second. This task earned them one sugar pellet. While the difficult task is for the rats to react to a light that flashed for only 0.2 seconds, which gave them two sugar pellets.
The rats completed the task under normal conditions and after they were given THC (tetrahydrocannabinol) and CBD (cannabidiol) independently and combined.

After the task, the researchers found that under normal conditions, the rats opted for the more difficult task which earning them a higher reward. While they opted for the easier task after being given THC.

The authors conclude that further research is warranted to determine the underlying mechanisms by which THC alters decision-making.