THC in marijuana makes rats lazy, less willing to try cognitively demanding tasks

Date: August 24, 2016

Source: University of British Columbia

New research from the University of British Columbia suggests there may be some truth to the belief that marijuana use causes laziness -- at least in rats.

The study, published today in the Journal of Psychiatry and Neuroscience, found that tetrahydrocannabinol (THC), the main psychoactive ingredient in marijuana, makes rats less willing to try a cognitively demanding task.

"Perhaps unsurprisingly, we found that when we gave THC to these rats, they basically became cognitively lazy," said Mason Silveira, the study's lead author and a PhD candidate in UBC's department of psychology. "What's interesting, however, is that their ability to do the difficult challenge was unaffected by THC. The rats could still do the task -- they just didn't want to."

For the study, researchers looked at the effects of both THC and cannabidiol (CBD) on rats' willingness to exert cognitive effort.

They trained 29 rats to perform a behavioural experiment in which the animals had to choose whether they wanted an easy or difficult challenge to earn sugary treats.

Under normal circumstances, most rats preferred the harder challenge to earn a bigger reward. But when the rats were given THC, the animals switched to the easier option, despite earning a smaller reward.

When they looked at the effect of CBD, an ingredient in marijuana that does not result in a high, researchers found the chemical did not have any effect on rats' decision-making or attention. CBD, which is believed to be beneficial in treating pain, epilepsy and even cancer, also didn't block the negative effects of THC.

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