Abstinence From Regular Cannabis Use Improves Memory Among Adolescents, Young Adults

medical marijuana
medical marijuana
Future studies need to determine whether improvement in cognition with abstinence is associated with improvement in academic and other functional outcomes.

Adolescents and young adults who abstained from cannabis for 4 weeks after regular use of the drug showed improvement in cognition compared with those who continued to use cannabis, according to the results of a study published in the Journal of Clinical Psychiatry.1

With the move toward legalization of cannabis in many states, there is concern that there may be greater adverse effects on adolescents than on older individuals as the result of neuromaturation that continues to occur into the third decade of life.2,3 To determine the effects of cannabis on cognition in adolescents and young adults, Randi Melissa Schuster, PhD, from the Center for Addiction Medicine, Department of Psychiatry, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts, and colleagues recruited 88 adolescents and young adults aged 16 to 25 years from the community and a local high school between July 2015 and December 2016. They randomly assigned participants to either the abstinence group (MJ-Abst; n=62) or the nonabstaining group (MJ-Mon; n=26).

The investigators verified abstinence by monitoring decreasing 11-nor-9-carboxy-Δ9-tetrahydrocannabinol urine concentration. They assessed attention and memory at baseline and weekly for 4 weeks with the Cambridge Neuropsychological Test Automated Battery.

Fifty-five individuals in the MJ-Abst group (88.7%) achieved biochemically confirmed 30-day continuous abstinence. Improvement in verbal learning occurred in the first week of abstinence. Better memory recall was observed in the MJ-Abst group than in the MJ-Mon group at weeks 1, 2, and 3. However, the investigators found no effect of abstinence on attention, with both groups improving alike.

The authors note that the absence of a control group of nonusers limited their ability to determine the effect of cannabis on domains that did not improve more among abstainers than nonabstainers, including attention, visual span capacity, short-term visual recognition memory, and verbal delayed recall. The authors noted that several possibilities may account for the failure to find differences in these domains with abstinence: that deficits existed before cannabis use, cannabis-induced deficits are permanent, practice effects in the control group may hinder the ability to detect differences between the groups, or cannabis has no adverse effects on those domains.

The authors call for more research to develop a better understanding of the cognitive effects of cannabis on adolescents and young adults, particularly in view of the effect such understanding is likely to have on local, state, and national policymaking.

Disclosures: John Evenden, PhD, has received advisory panel payments from H. Lundbeck A/S, and is a former employee of AstraZeneca. Eden Evins, MD, has received research grant support to her institution from Pfizer and Reckitt Benckiser for work unrelated to this project.


  1. Scuster RM, Gilman J, Schoenfeld D, et al. One month of cannabis abstinence in adolescent and young adults is associated with improved memory. J Clin Psychiatry. 2018;79(6):17m11977.
  2. Giedd JN, Blumenthal J, Jeffries NO, et al. Brain development during childhood and adolescence: a longitudinal MRI study. Nat Neurosci. 1999;2(10):861-863.
  3. Sowell ER, Thompson PM, Holmes CJ, Batth R, Jernigan TL, Toga AW. Localizing age-related changes in brain structure between childhood and adolescence using statistical parametric mapping. Neuroimage. 1999;9(6 Pt 1):587-597.