It’s no secret using cannabis impairs thinking and interferes with one’s ability to learn and perform complicated tasks. Reaction time and coordination are also negatively affected, which is why driving while under the influence of cannabis can be dangerous. But a new massive study, which merged the findings of over 10 meta-analyses comprising more than 43,000 people, found that cognitive impairments may linger well beyond the initial period of intoxication.

Cannabis brain fog

As cannabis legalization for both medical and recreational use has been amped up in recent years, most notably in North America, scientists are starting to have a more nuanced understanding of the long-term effects of cannabis. That’s important since cannabis is the most consumed psychoactive substance in the world, after alcohol and nicotine, despite its illicit status in most countries.

The highest rates of cannabis use are among adolescents and young adults. These groups are also the most susceptible to cannabis-induced cerebral alterations as a result of the activation of CB1 receptors in the frontoparietal and frontostriatal regions of the brain. It is therefore important to understand the cognitive risks of using cannabis.

With this in mind, researchers in Canada looked at the effects of cannabis on more than 43,000 people, both in the short and long term.

The study found that cannabis use was associated with small to moderate cognitive impairments in areas such as decision making, learning, and remembering through listening and reading, as well as extending the time someone needs to complete mental tasks. All these effects are dose-dependent and may vary due to tolerance. Genetics and underlying mental health disorders also can weigh heavily, which is why the degree of cognitive impairment can vary wildly from user to user.

“Our study enabled us to highlight several areas of cognition impaired by cannabis use, including problems concentrating and difficulties remembering and learning, which may have a considerable impact on users’ daily lives,” wrote Dr. Alexandre Dumais, an associate clinical professor of psychiatry at Université de Montréal and a study co-author.

These sorts of results have been highlighted by other studies before, so nothing groundbreaking thus far. But one of the findings that stood out was that some of these effects linger for a significant amount of time after intoxication wears off.

THC, the main psychoactive cannabinoid found in cannabis, is fat-soluble. Thus, it can stay stored in body fat and may gradually be released into the bloodstream for weeks. As such, there may be ‘residual’ cognitive effects that can persist long after acute intoxication has subsided. Although mild, these residual effects may remain significant after 25 days of abstinence from THC, especially among heavy users.

“Cannabis use in youth may consequently lead to reduced educational attainment, and, in adults, to poor work performance and dangerous driving. These consequences may be worse in regular and heavy users,” said Dumais.

The findings appeared in the journal Addiction.