Cannabis is one of the most consumed psychoactive substances in the world, behind only alcohol and nicotine. Adolescents and young adults use the most cannabis.
THC is the main psychoactive ingredient in the cannabis plant. Cannabis activates receptors in many parts of the thinking brain, including the hippocampus (memory processor), amygdala (panic button), and cerebellum (balance), causing cognitive alterations. Cannabis intoxication can last several hours, but because cannabis is fat-soluble and stored in body fat, it can also be released into the bloodstream for months.
Prior research has demonstrated lasting cognitive impairments, beyond the intoxication period, in learning, memory, attention, and executive function. Researchers sought to synthesize the current evidence on the immediate and residual effects of cannabis use on cognition. They reviewed 10 meta-analyses (conducted a review of reviews) that incorporated quantitative examinations of performance on cognitive tasks by over 43,000 adolescent and adult participants in the general population.
Verbal learning and memory (learning from reading or listening and remembering what was learned) were the most impaired during and after cannabis intoxication.
Participants suffered small-to-moderate negative effects, during and after cannabis use, in:
- Executive Functioning (planning, reasoning),
- Working Memory,
- Decision-making, and
- Attention and Processing Speed (found in heavy cannabis-using youths).
Small deficits in inhibitory processes (suppressing inappropriate responses) and flexibility were also observed.
Cannabis use may lead to problems with education attainment, school and work performance, and driving. Researchers recommended more education and treatment opportunities be provided to the public.
Takeaway: The detrimental cognitive effects of cannabis use persist beyond intoxication. Limit or eliminate cannabis use to better protect learning, memory, decision-making, planning, and reasoning.
Laura Dellazizzo, et al., Evidence on the Acute and Residual Neurocognitive Effects of Cannabis Use in Adolescents and Adults: A Systematic Meta-Review of Meta-Analyses, Addiction. 2021; 1-14, https://onlinelibrary.wiley.com/doi/epdf/10.1111/add.15764.