Bottom Line: Frequent cannabis use by adolescents and young adults was associated with small reductions in cognitive function that appeared to diminish with abstinence over time.
Why The Research Is Interesting: The legality of cannabis and public perceptions of it have shifted in the United States. However, scientific debates about the physical and mental health consequences of cannabis are unresolved.
Who and When: 69 studies published between 1973 and 2017 including 2,152 cannabis users and 6,575 individuals with minimal cannabis use for comparison
What (Study Measures): Results from cognitive tests administered in studies
How (Study Design): This was a systematic review and meta-analysis. A meta-analysis combines the results of multiple studies identified in a systematic review and quantitatively summarizes the overall association between the same exposure and outcomes across all studies.
Authors: J. Cobb Scott, Ph.D., of the University of Pennsylvania Hospital, Philadelphia, and coauthors
Results: Small cognitive effects were associated with heavy/frequent cannabis use among adolescents and young adults and the results suggest they faded substantially with abstinence longer than 72 hours.
Study Limitations: Consideration of other relevant factors is needed when interpreting the results, including that use of all psychoactive substances is associated with risk, that functional outcomes may be more important than measures of cognitive function, and the study cannot make causal conclusions about marijuana and cognitive functioning.
Study Conclusions: Although continued cannabis use may be associated with small reductions in cognitive functioning, results suggest that cognitive deficits are substantially diminished with abstinence.