One Month of Cannabis Abstinence in Adolescents and Young Adults Is Associated With Improved Memory

Abstract

Objective: Associations between adolescent cannabis use and poor neurocognitive functioning have been reported from cross-sectional studies that cannot determine causality. Prospective designs can assess whether extended cannabis abstinence has a beneficial effect on cognition.

Methods: Eighty-eight adolescents and young adults (aged 16-25 years) who used cannabis regularly were recruited from the community and a local high school between July 2015 and December 2016. Participants were randomly assigned to 4 weeks of cannabis abstinence, verified by decreasing 11-nor-9-carboxy-∆⁹-tetrahydrocannabinol urine concentration (MJ-Abst; n = 62), or a monitoring control condition with no abstinence requirement (MJ-Mon; n = 26). Attention and memory were assessed at baseline and weekly for 4 weeks with the Cambridge Neuropsychological Test Automated Battery.

Results: Among MJ-Abst participants, 55 (88.7%) met a priori criteria for biochemically confirmed 30-day continuous abstinence. There was an effect of abstinence on verbal memory (P = .002) that was consistent across 4 weeks of abstinence, with no time-by-abstinence interaction, and was driven by improved verbal learning in the first week of abstinence. MJ-Abst participants had better memory overall and at weeks 1, 2, 3 than MJ-Mon participants, and only MJ-Abst participants improved in memory from baseline to week 1. There was no effect of abstinence on attention: both groups improved similarly, consistent with a practice effect.

Conclusions: This study suggests that cannabis abstinence is associated with improvements in verbal learning that appear to occur largely in the first week following last use. Future studies are needed to determine whether the improvement in cognition with abstinence is associated with improvement in academic and other functional outcomes.

Trial registration: ClinicalTrials.gov identifier: NCT03276221.

Figure 1.

A total of 592 valid urine specimens were collected during the study period, and 93.2% (n = 552) of the specimens had THCCOOH levels that were quantifiable based on available laboratory methods (range of creatinine-unadjusted THCCOH levels in quantifiable samples: 0 – 3920ng/ml; range of creatinine-adjusted THCCOH levels in quantifiable samples: 0 – 1765.8ng/mg). Urine creatinine-adjusted THCCOOH concentrations declined during four weeks of monitored cannabis abstinence only among those randomized to 4 weeks of cannabis abstinence (MJ-Abst). Values are presented for specimens where quantifiable THCCOOH and creatinine were available. All values represent means and standard errors.

Figure 2.

A. Attention improved similarly in MJ-Abst and MJ-Mon across the 4-week assessment period. All values represent means and standard errors. B. Memory improved only in MJ-Abst, and this improvement occurred in the first week of cannabis abstinence. All values represent means and standard errors.