Association of Cannabis With Cognitive Functioning in Adolescents and Young Adults: A Systematic Review and Meta-analysis
Jama Psychiatry
Frequent cannabis use mildly inhibits cognitive functioning. After 72 hours or more of abstinence, however, these effects are no longer present. These are the main findings from an article that complied 69 relevant studies, which included over 8000 adolescents and young adults, and analyzed their data together.
The researchers found a small difference between people who frequently use cannabis and non-cannabis users in terms of cognitive functions such as attention, learning, and memory. To give an idea of how large an effect they found, if we were to randomly select one person from each group, the non-cannabis user would have performed better on tests of cognitive function about 57% of the time—a small effect. If we depict the performance of the two groups on a graph, 90% of the data from the two groups would overlap (enter 0.25 into this website for a visualization of the effect size).
The effect size in real life, however, is likely a bit smaller the researchers argue. The studies included in this meta-analysis display some bias and do not fully account for confounding factors, such as socioeconomic status. If these factors were fully accounted for, we might expect a randomly selected non-cannabis user to outperform a frequent cannabis user about 54% of the time, and about 95% of the data from the two groups to overlap.
The researchers also found that age at first cannabis use, sociodemographic characteristics, clinical characteristics (e.g., depression), and the year the included study was published were not indicative of whether cannabis use affected cognitive functioning. In contrast, longer abstinence periods were associated with a smaller effect. When the researchers considered only studies that mandated a 72-hour cannabis abstinence period, there was no difference in cognitive functioning between frequent cannabis users and non-users.
As a final note, it’s important to consider that this study focuses only on cognitive functioning. From this data, we cannot make statements about whether cannabis use impacts physical and mental health outcomes, such as lung function, motivation, or psychosis.
For the original article, click here.
Scott JC, Slomiak ST, Jones JD, et al. Association of Cannabis With Cognitive Functioning in Adolescents and Young Adults: A Systematic Review and Meta-analysis. Jama Psychiatry. 2018 Jun;75(6):585-595. DOI: 10.1001/jamapsychiatry.2018.0335.