It’s long been suspected that smoking pot makes you lazy and now science has proved it. 

Researchers from the University of British Columbia, Canada, gave the chemical tetrahydrocannabinol (THC), the main brain-affecting ingredient in cannabis, to laboratory rats. 

Investigators trained 29 rats to participate in a behavioral experiment where the rodents had to choose whether they wanted an easy or difficult challenge to earn sugary treats. 

“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. “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.”

At the beginning rats chose between two levers to signal whether they wanted an easy or hard challenge. Choosing the easy challenge resulted in a light turning on for one second, which the rats could easily detect and respond to by poking it with their nose, receiving one sugar pellet as a reward. 

In the more difficult challenge, the light turned on for only 0.2 seconds, rewarding the rat with two sugar pellets if they responded with a nose poke. 

“Under normal circumstances, most rats preferred the harder challenge to earn a bigger reward. But when the rats were given THC, they switched to an easier option, despite earning a smaller reward,” explained Silveira.

In further experiments investigators were able to link this behavioral effect to a specific region of the brain.

“We hope to directly administer a THC-like drug into that region and see if we can recreate the decision-making impairment we observed,” Silveira added. “Being able to localize this effect to a certain brain region, or network, provides us with an opportunity to try and selectively block it.”

In the future, investigators will give THC to rats for an extended period of time, to see how it affects decision-making processes in the long-term, because some people tend to use cannabis chronically and this can have different effects on the brain and behavior. 

“While cannabis helps a lot of people, there are certain effects that they may want to be wary of before they take it. With cannabis law reform imminent in many countries, it is imperative that more research is devoted to the topic,” said Silveira. “I really hope governments make it easier for labs to conduct human cannabis studies, because that will be the best way to inform future policy.”

-Dmitry Belyaev