Associations between cannabis use and cognitive functioning in adolescents and young adults are small, according to a study published in JAMA Psychiatry.

J. Cobb Scott, PhD, from the Department of Psychiatry at the Perelman School of Medicine, University of Pennsylvania in Philadelphia, and colleagues, searched through observational, cross-sectional studies to provide the first quantitative synthesis of literature examining cannabis and cognitive functioning in adolescents and young adults with a mean age of 26 years and younger.

A total of 69 eligible studies with 8,727 participants were analyzed (2,152 cannabis users and 6,575 comparison participants who had minimal cannabis use).  Cannabis users had a mean (SD) age of 20.6 (2.8) years and were 68.1% male. Comparison participants had a mean (SD) age of 20.8 (3.4) years and were 55.8% male. Studies were predominantly conducted in the United States, United Kingdom, Europe, and Australia. Cannabis users had a mean (SD) age at cannabis use initiation of 15.2 (1.5) years.

Continue Reading

The mean (SD) time of abstinence required by the studies was 152.7 (335.2) hours. Twenty-two studies (32%) reported either 0 hours of abstinence or no specificity in abstinence criteria, 32 studies (46%) reported between 1 and 72 hours of abstinence, and 15 studies (22%) reported greater than 72 hours of abstinence.

Results indicated a small overall effect size (presented as mean d) for reduced cognitive functioning associated with frequent or heavy cannabis use (d, −0.25). The magnitude of effect sizes did not vary by sample age or age at cannabis use onset. However, studies requiring an abstinence period longer than 72 hours (15 studies; n = 928) had an overall effect size (d, −0.08) that was not significantly different from 0 and smaller than studies with less stringent abstinence criteria (54 studies; n = 7,799; d, −0.30).

Related Articles

“Associations between cannabis use and cognitive functioning in cross-sectional studies of adolescents and young adults are small and may be of questionable clinical importance for most individuals,” the researchers concluded. “Furthermore, abstinence of longer than 72 hours diminishes cognitive deficits associated with cannabis use.”


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. 18 April 2018 [Published online ahead of print]. doi:10.1001/jamapsychiatry.2018.0335