Researchers find lab rats given marijuana to be lazy


The main psychoactive ingredient in cannabis (hemp), THC, makes lab rats less willing to exert cognitive effort according to University of British Columbia researchers. Usually, rats preferred taking part in harder tasks, but after being dosed with THC, the same rats picked the easier task.

This research was published on Tuesday in the Journal of Psychiatry and Neuroscience, it looked at the effects of both THC – the drug’s main active ingredient – and the non-psychoactive compound cannabidiol, or CBD, on the male lab rats’ willingness to exert cognitive effort. 29 rats were trained on two different challenges: rats which successfully carried out the more difficult task earned two sugar pellets; those which carried out the easier task earned just one.

According to the study’s lead author, Mason Silveira, a PhD candidate in psychology at the University of British Columbia, the THC did not make the rats less intelligent, it just made them just lazier.

When rats were given THC – the active ingredient in cannabis or marijuana – we found that they were less likely to exert the mental energy needed to do more difficult tasks.

“What’s particularly interesting is though they were less likely to do these more difficult tasks they were still able to. There’s this distinction between THC’s ability to affect your cognition versus your willingness to actually use your cognitive abilities.”

The researchers said more research is needed to determine the impact of THC on the human brain, to explore how the potential negative effects could be mitigated and also to look into the effect of other marijuana compounds other than CBD on THC’s impact.

Our research highlights that, yes, cannabis itself may be beneficial for a variety of things, but can maybe lead to these impairments in cognition that you might want to consider – Mason Silveira.

CBD, is believed to have medicinal benefits such as relieving pain and the symptoms of epilepsy, it had no impact on the rats’ cognitive behaviour. It also did not mitigate the cognitive impact of THC in the rats.

Tetrahydrocannabinol (THC, dronabinol by INN), is the principal psychoactive constituent (or cannabinoid) of cannabis. It can be an amber or gold colored glassy solid when cold, which becomes viscous and sticky if warmed.


Cannabis, also known as marijuana among other names, is a preparation of the Cannabis plant intended for use as apsychoactive drug or medicine. The main psychoactive part of cannabis is tetrahydrocannabinol (THC); one of 483 known compounds in the plant, including at least 65 other cannabinoids. Cannabis can be used by smoking, vaporization, within food, or as an extract.

Cannabis is often used for its mental and physical effects, such as a “high” or “stoned” feeling, a general change in perception,euphoria (heightened mood), and an increase in appetite. Short term side effects may include a decrease in short-term memory, dry mouth, impaired motor skills, red eyes, and feelings of paranoia or anxiety. Long term side effects may include addiction, decreased mental ability in those who started as teenagers, and behavioral problems in children whose mothers used cannabis during pregnancy. Onset of effects is within minutes when smoked and about 30 to 60 minutes when cooked and eaten. They last for between two and six hours.

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