Early onset marijuana use is associated with learning inefficiencies

Semantic clustering on common list-learning tasks: a systematic review of the state of the literature and recommendations for future directions

INTRODUCTION

On some list-learning tasks, such as the California Verbal Learning Test (CVLT) or Hopkins Verbal Learning Test (HVLT), examinees have the opportunity to group words based on semantically related categories (i.e., semantic clustering). Semantic clustering (SC) is often considered the most efficient organizational strategy and adopting SC is presumed to improve learning and memory. In addition, SC is conceptualized as reflecting higher-order executive functioning skills. Although SC measures have intuitive appeal, to date, there are no comprehensive reviews of the SC literature base that summarize its psychometric utility. In this systematic review, we synthesize the literature to judge the validity of SC scores.

METHOD

We conducted a systematic literature search for empirical articles reporting SC from the CVLT and HVLT. We qualitatively described the relationship of SC with other list-learning and cognitive test scores and clinical diagnoses, contrasting SC with serial clustering and total learning scores when possible.

RESULTS

SC was inversely correlated with serial clustering. Higher SC was strongly associated with better learning and memory performances. When compared with cognitive tests, SC tended to have the strongest relationships with other memory measures and modest relationships with tests of executive functioning. SC had negligible to small relationships with most other cognitive domains. Traditional memory scores yielded stronger relationships to cognitive test performances than did SC. SC across clinical groups varied widely, but clinical groups tended to use SC less often than healthy comparison groups.

CONCLUSION

Our comprehensive review of the literature revealed that SC is strongly related to measures of learning and memory on the CVLT and HVLT and is correlated with a wide range of cognitive functions. SC has been understudied in relevant populations and additional research is needed to test the degree to which it adds incremental validity beyond traditional measures of learning and memory.

Longitudinal Associations Between Cannabis Use and Cognitive Impairment in a Clinical Sample of Middle-Aged Adults Using Cannabis for Medical Symptoms

Introduction: Cannabis use to alleviate medical symptoms is increasing in middle-aged and older adults. Cognitive impairment associated with cannabis use may be especially detrimental to these understudied age groups. We hypothesized that among middle-aged and older adults who used cannabis for 12 months, frequent (≥3 days/week) compared with nonfrequent (≤2 days/week) use will be associated with cognitive impairment. Materials and Methods: We performed secondary analysis on data from a clinical trial of cannabis use for medical symptoms. Participants (n=62) were ≥45 years, and completed a baseline and at least one postbaseline visit. Cognitive domains were assessed through the Cambridge Neuropsychological Test Automated Battery. Cannabis use was assessed prospectively through daily smartphone diaries. Frequency of cannabis use was a binary predictor in a mixed-effects logistic regression model predicting cognitive impairment adjusted for baseline cognitive functioning. Results: At baseline, participants were primarily nonfrequent cannabis users; however, in all other time periods, most participants were frequent users (range: 55-58%). Cognitive outcomes did not differ between frequent and nonfrequent cannabis users. However, in sensitivity analyses, respondents with problematic cannabis use scored significantly worse on one cognitive domain compared to those without problematic cannabis use. Conclusions: In a clinical sample of adults aged ≥45 years, no longitudinal associations were found between cannabis use and cognitive functioning. However, a few significant associations were observed between problematic use and cognitive functioning. Further research is needed to assess the impact of cannabis use on adults, particularly those aged ≥65 years, and to investigate potential subtler influences of cannabis use on cognition. ClinicalTrials.gov ID: NCT03224468.

Prospective, longitudinal study to isolate the impacts of marijuana use on neurocognitive functioning in adolescents

Introduction

Policies to legalize possession and use of marijuana have been increasingly supported across the United States. Although there are restrictions on use in minors, many substance abuse scientists anticipate that these policy changes may alter use patterns among adolescents due to its wider availability and a softening of beliefs about its potentially harmful consequences. Despite the possibility that these policies may increase the prevalence of use among adolescents, the effects of marijuana on neurodevelopment remain unclear, clouding arguments in favor of or opposition to these policies.

Methods

The present prospective, longitudinal study was designed to isolate the neurodevelopmental consequences of marijuana use from its precursors during adolescence-a period of heightened vulnerability for both substance use and disrupted development due to environmental insults. Early adolescents who were substance-naïve at baseline (N = 529, aged 10-12) were recruited and tracked into adolescence when a subgroup initiated marijuana use during one of three subsequent waves of data collection, approximately 18 months apart.

Results

Results suggest that marijuana use may be specifically related to a decline in verbal learning ability in the short term and in emotion recognition, attention, and inhibition in the longer-term.

Discussion

These preliminary findings suggest that marijuana use has potential to adversely impact vulnerable neurodevelopmental processes during adolescence. Intensive additional investigation is recommended given that state-level policies regulating marijuana use and possession are rapidly shifting in the absence of good scientific information.

The International Cannabis Toolkit (iCannToolkit): a multidisciplinary expert consensus on minimum standards for measuring cannabis use

BACKGROUND

The lack of an agreed international minimum approach to measuring cannabis use hinders the integration of multidisciplinary evidence on the psychosocial, neurocognitive, clinical and public health consequences of cannabis use.

METHODS

A group of 25 international expert cannabis researchers convened to discuss a multidisciplinary framework for minimum standards to measure cannabis use globally in diverse settings.

RESULTS

The expert-based consensus agreed upon a three-layered hierarchical framework. Each layer-universal measures, detailed self-report and biological measures-reflected different research priorities and minimum standards, costs and ease of implementation. Additional work is needed to develop valid and precise assessments.

CONCLUSIONS

Consistent use of the proposed framework across research, public health, clinical practice and medical settings would facilitate harmonisation of international evidence on cannabis consumption, related harms and approaches to their mitigation.

The externalizing and internalizing pathways to marijuana use initiation: Examining the synergistic effects of impulsiveness and sensation seeking

Adolescent marijuana use has become increasingly more problematic compared with the past; thus, understanding developmental processes that increase the liability of marijuana use is essential. Two developmental pathways to adolescent substance use have been proposed: an externalizing pathway that emphasizes the expression of aggressive and delinquent behavior, and an internalizing pathway that emphasizes the role of depressive symptoms and negative affect. In this study, we aimed to examine the synergistic role of impulsiveness and sensation seeking in the two risk pathways to determine whether both high and low levels of the traits are risk factors for marijuana use. Our study included 343 adolescents (52% were girls, 78% identified as Hispanic) that oversampled high-risk youth (78% had a family history of substance use disorder), assessed biannually between the ages of 13-16 years old. Moderated mediation analyses revealed that high levels of sensation seeking indirectly predicted marijuana use through higher mean levels of externalizing behavior. The positive relationship between sensation seeking and externalizing behavior was only significant at high levels of impulsiveness. Conversely, low levels of sensation seeking indirectly predicted marijuana use through higher mean levels of internalizing behavior. The negative relationship between sensation seeking and internalizing behavior was only significant at low levels of impulsiveness. Collectively, these results demonstrate that high and low levels of both impulsiveness and sensation seeking confer increased risk of marijuana use, albeit through different mechanisms. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Sex Differences in Neuropsychological Functioning are Domain-Specific in Adolescent and Young Adult Regular Cannabis Users

OBJECTIVE

Adolescence into young adulthood represents a sensitive period in which brain development significantly diverges by sex. Regular cannabis use by young people is associated with neuropsychological vulnerabilities, but the potential impact of sex on these relationships is unclear.

METHOD

In a cross-sectional study, we examined sex differences in multi-domain neuropsychological functioning using the Cambridge Neuropsychological Test Automated Battery (CANTAB) and tested whether sex moderated the relationship between cognitive performance and age of initiation, frequency of cannabis use, amount of cannabis use, and withdrawal symptoms in at least weekly adolescent and young adult cannabis users (n = 171; aged 13-25 years; 46.2% female).

RESULTS

Male cannabis users had poorer visual recognition memory and female cannabis users showed worse attention and executive functions, with medium to large effect sizes. These sex effects persisted, when controlling for age, IQ, amount of alcohol and nicotine use, mood and anxiety symptoms, emotional stability and impulsive behavior. Earlier age of initiated use and more use were associated with worse attentional functions in females, but not males. More use was more strongly associated with worse episodic memory in males than in females. More use was associated with poorer learning in males only.

CONCLUSIONS

Domain-specific patterns of neuropsychological performance were found by sex, such that males showed poorer visual memory and females showed worse performance on measures of attention (sustained visual, multitasking) and executive functioning (spatial planning/working memory subdomains). Larger studies including healthy controls are needed to determine if the observed sex differences are more exaggerated relative to non-users.

A longitudinal study of the impact of marijuana on adult memory function: Prenatal, adolescent, and young adult exposures

More Americans are using marijuana than in previous decades but there are concerns over its long-term impact on cognitive functioning, especially memory. The literature on marijuana use and cognitive functioning is mixed, with some studies showing recovery of functioning upon abstinence from the drug and others showing long-term effects that persist. The latter seems especially true for individuals who initiate marijuana at a younger age and engage in more chronic patterns of use. The goal of the current study is to use prospectively collected data on young adults from a prenatal cohort to determine if there is an effect of early and/or current marijuana use on young adult memory, controlling for prenatal exposure to marijuana use, childhood memory deficits, and other significant covariates of memory functioning. At the 22-year follow-up phase of the Maternal Health Practices and Child Development (MHPCD) study, 524 young adults (58% Black, 42% White, 52% female) completed the Wechsler Memory Scale-III. Multiple regression analyses and structural equation modeling were used to determine the effect of marijuana exposure during gestation, early adolescence, and young adulthood on young adult memory function. Results indicated that initiating marijuana use before age 15 placed young adults at greater risk of memory deficits, even after controlling for childhood memory and current marijuana use. First trimester marijuana exposure also indirectly predicted young adult memory function via childhood memory deficits and early initiation of marijuana. These findings highlight the risk of prenatal marijuana exposure and early initiation of marijuana for long-term memory function in adulthood.

The Role of Safety Behaviors in the Relationship between Social Anxiety and Marijuana Use Problems

Background: Social anxiety has been associated with higher levels of and more problematic marijuana use. Research suggests that safety behaviors may play a role in the development and maintenance of marijuana problems. However, the safety behaviors that are most commonly associated with social anxiety have not been investigated, nor has the potential moderating role of gender on this relationship. Method: A diverse sample of regular marijuana users (N = 279) completed measures of social anxiety, safety behaviors related to social situations, and marijuana use problems. Results: Social anxiety and safety behavior use were both positively correlated with marijuana use problems. These relationships were stronger in men than in women. Among men only, tendencies to use safety behaviors to cope with social situations accounted for the relationship between social anxiety symptoms and marijuana-related problems. Discussion: The avoidant coping style that characterizes safety behaviors in social anxiety may also underlie problematic patterns of marijuana use, particularly for men. The present study is the first to report an association between safety behaviors in social situations and marijuana use problems and suggests the importance of examining the effect of reducing safety behaviors in social situations, in regular marijuana users with comorbid social anxiety.

Attitudes, Subjective Norms, and Perceived Behavioral Control Associated with Age of First Use of Cannabis among Adolescents

BACKGROUND

Prevention of early age initiation of cannabis use is a national priority, highlighting the importance of identifying cannabis-specific attitudes, norms, and perceived behavioral control in relation to initiation age.

METHODS

Data were from the NEXT Generation Health Study, a national longitudinal sample of US adolescents followed from 10th grade (N = 1850). Cannabis-specific attitudes, norms, and perceived behavioral control were assessed at 10th grade. Age of first use was reported retrospectively 2-3 years after high-school and participants were categorized as early initiators (<14 years; 3.8%), high-school (HS) initiators (14-18 years; 35.6%), post-HS initiators (>18 years; 8.3%), or never users (52.3%).

RESULTS

Relative to never users, early initiators were more likely to endorse pro-use attitudes (AOR [adjusted odds ratio] = 2.39, 95% confidence interval [CI] = 1.27-4.50), less disapproving parental attitudes toward use (AOR = 2.50, 95% CI = 1.45-4.28), higher cannabis use among friends (AOR = 3.81, 95% CI = 2.21-6.60), and higher ease of access (AOR = 2.10, 95% CI = 1.14-3.87); HS initiators were similarly more likely to report less disapproving attitudes toward use (AOR = 1.55, 95% CI = 1.25-1.91), higher cannabis use among friends (AOR = 2.81, 95% CI = 2.18-3.65), and higher ease of access (AOR = 1.66, 95% CI = 1.21-2.28).

CONCLUSIONS

Earlier cannabis initiation was associated with more favorable cannabis attitudes, subjective norms, and perceived behavioral control, highlight these variables as potential intervention targets.

Marijuana use and major depressive disorder are additively associated with reduced verbal learning and altered cortical thickness

Marijuana (MJ) use and major depressive disorder (MDD) have both been associated with deficits in verbal learning and memory as well as structural brain abnormalities. It is not known if MJ use by those with MDD confers additional impairment. The goal of this study was to examine unique and combined effects of MDD and MJ use on verbal memory and brain structure. Young adults (n=141) aged 18-25 years with MJ use and no lifetime MDD (MJ, n=46), MDD and no MJ use (MDD, n=23), MJ use and lifetime MDD (MDD+MJ, n=24), and healthy controls without MDD or MJ use (CON, n=48) were enrolled. Participants completed the California Verbal Learning Test, Second Edition (CVLT-II), a measure of verbal learning and memory. A sub-sample of 82 participants also underwent a structural magnetic resonance imaging (MRI) scan. Group differences in CVLT-II performance, cortical thickness, and hippocampal volume were assessed. We found an additive effect of MDD and MJ on memory recall. Only MDD, but not MJ, was associated with poorer initial learning, fewer words recalled, more intrusion errors, and lower percent retention. There was also an additive effect of MDD and MJ use on reduced cortical thickness in the middle temporal gyrus. Findings indicate that MJ use and MDD have additive adverse associations with verbal recall and cortical thickness in the middle temporal gyrus, suggesting that MJ use among those with MDD may be contraindicated. Prospective studies are warranted to determine whether this association may be causal.

Do Differences in Learning Performance Precede or Follow Initiation of Marijuana Use?

OBJECTIVE

Studies examining cross-sectional associations between age at marijuana initiation and memory deficits yield mixed results. Because longitudinal data are sparse, controversy continues regarding whether these deficits reflect premorbid risk factors or sequelae of early marijuana initiation; here, we examine this question in a community sample followed since birth.

METHOD

Masked examiners administered four subtests of the Wide Range Assessment of Memory and Learning (WRAML/WRAML2) from childhood until young adulthood to 119 urban, predominantly African American participants. Multivariable generalized estimated equation models measured longitudinal trajectories of learning. Participants were grouped as never users (n = 26), later initiators (≥16 years old; n = 31), and earlier initiators of marijuana use (n = 62).

RESULTS

Marijuana onset groups did not significantly differ on WRAML scaled scores or IQ in childhood, nor did they differ on WRAML scaled scores in adolescence. On most WRAML2 subtests, these groups did not significantly differ in young adulthood after taking into account sex and childhood IQ. However, on Story Memory, later initiators attained higher scaled scores in young adulthood, even after including additional covariates of anxiety, depression, postsecondary education, past-month marijuana use, and past-week high-risk drinking. They showed a significantly more positive trajectory than never users that was driven by within-group improvement after adolescence. Earlier initiators showed within-group decline in Story Memory after adolescence.

CONCLUSIONS

Differences in learning following earlier initiation of marijuana use may not be solely attributable to premorbid deficits.

Recreational cannabis use impairs driving performance in the absence of acute intoxication

BACKGROUND

Across the nation, growing numbers of individuals are exploring the use of cannabis for medical or recreational purposes, and the proportion of cannabis-positive drivers involved in fatal crashes increased from 8 percent in 2013 to 17 percent in 2014, raising concerns about the impact of cannabis use on driving. Previous studies have demonstrated that cannabis use is associated with impaired driving performance, but thus far, research has primarily focused on the effects of acute intoxication.

METHODS

The current study assessed the potential impact of cannabis use on driving performance using a customized driving simulator in non-intoxicated, heavy, recreational cannabis users and healthy controls (HCs) without a history of cannabis use.

RESULTS

Overall, cannabis users demonstrated impaired driving relative to HC participants with increased accidents, speed, and lateral movement, and reduced rule-following. Interestingly, however, when cannabis users were divided into groups based on age of onset of regular cannabis use, significant driving impairment was detected and completely localized to those with early onset (onset before age 16) relative to the late onset group (onset ≥16 years old). Further, covariate analyses suggest that impulsivity had a significant impact on performance differences.

CONCLUSIONS

Chronic, heavy, recreational cannabis use was associated with worse driving performance in non-intoxicated drivers, and earlier onset of use was associated with greater impairment. These results may be related to other factors associated with early exposure such as increased impulsivity.

A Systematic Review of Human Neuroimaging Evidence of Memory-Related Functional Alterations Associated with Cannabis Use Complemented with Preclinical and Human Evidence of Memory Performance Alterations

Cannabis has been associated with deficits in memory performance. However, the neural correlates that may underpin impairments remain unclear. We carried out a systematic review of functional magnetic resonance imaging (fMRI) studies investigating brain functional alterations in cannabis users (CU) compared to nonusing controls while performing memory tasks, complemented with focused narrative reviews of relevant preclinical and human studies. Twelve studies employing fMRI were identified finding functional brain activation during memory tasks altered in CU. Memory performance studies showed CU performed worse particularly during verbal memory tasks. Longitudinal studies suggest that cannabis use may have a causal role in memory deficits. Preclinical studies have not provided conclusive evidence of memory deficits following cannabinoid exposure, although they have shown evidence of cannabinoid-induced structural and histological alteration. Memory performance deficits may be related to cannabis use, with lower performance possibly underpinned by altered functional activation. Memory impairments may be associated with the level of cannabis exposure and use of cannabis during developmentally sensitive periods, with possible improvement following cessation of cannabis use.

The Changing Legal Landscape of Cannabis Use and Its Role in Youth-onset Psychosis

The rapidly changing landscape of cannabis in terms of availability, potency, and routes of administration, as well as the decrease in risk perception and changing norms, have contributed to an increase in the popularity of cannabis. Cannabis use is associated with a poorer recovery from a psychotic disorder, increasing the risk of relapse, rehospitalization, and lower social functioning. Data are mixed regarding cannabis use as a component cause of psychosis in people at risk for psychotic disorder. Care providers, parents, and schools must educate youth and adolescents about the risks of cannabis use.

Short-term effects of cannabis consumption on cognitive performance in medical cannabis patients

This observational study examined the acute cognitive effects of cannabis. We hypothesized that cognitive performance would be negatively affected by acute cannabis intoxication. Twenty-two medical cannabis patients from Southwestern Ontario completed the study. The majority (n = 13) were male. Mean age was 36.0 years, and mean level of education was 13.7 years. Participants were administered the same brief neurocognitive battery three times during a six-hour period: at baseline ("Baseline"), once after they consumed a 20% THC cannabis product ("THC"), and once again several hours later ("Recovery"). The average self-reported level of cannabis intoxication prior to the second assessment (i.e., during THC) was 5.1 out of 10. Contrary to expectations, performance on neuropsychological tests remained stable or even improved during the acute intoxication stage (THC; d: .49-.65, medium effect), and continued to increase during Recovery (d: .45-.77, medium-large effect). Interestingly, the failure rate on performance validity indicators increased during THC. Contrary to our hypothesis, there was no psychometric evidence for a decline in cognitive ability following THC intoxication. There are several possible explanations for this finding but, in the absence of a control group, no definitive conclusion can be reached at this time.

The effects of cannabinoid 1 receptor compounds on memory: a meta-analysis and systematic review across species

RATIONALE

While cannabis-based medicinal products have been shown to be effective for numerous neurological and psychiatric disorders, the evidence base regarding their adverse cognitive effects is poorly understood. The cannabinoid 1 receptor modulates memory performance via intracellular and extracellular mechanisms that alter synaptic transmission and plasticity. While previous literature has consistently shown that chronic cannabis users exhibit marked cognitive impairments, mixed findings have been reported in the context of placebo-controlled experimental trials. It is therefore unclear whether these compounds inherently alter cognitive processes or whether individuals who are genetically predisposed to use cannabis may have underlying cognitive deficits.

OBJECTIVE

We conducted a meta-analysis to investigate the effects of full and partial cannabinoid 1 receptor (CB1R) agonists, antagonists, and negative allosteric modulators on non-spatial and spatial memory.

METHODS

In accordance with the PRISMA guidelines, the EMBASE, MEDLINE, and PsycINFO databases were systematically searched for studies examining the effects of CB1R agonists, antagonists, and negative allosteric modulators on memory performance.

RESULTS

We systematically reviewed 195 studies investigating the effects of cannabinoid compounds on memory. In humans (N = 35 studies, comprising N = 782 subjects), delta-9-tetrahydrocannabinol (THC) (1.5-5 mg/kg) relative to placebo impaired performance on non-spatial memory tests, whereas only high THC doses (67 mg/kg) impaired spatial memory. Similarly, THC (0.2-4 mg/kg) significantly impaired visuospatial memory in monkeys and non-human primates (N = 8 studies, comprising N = 71 subjects). However, acute THC (0.002-10 mg/kg) had no effect on non-spatial (N = 6 studies, comprising 117 subjects; g = 1.72, 95% confidence interval (CI) - 0.18 to 3.63, p = 0.08) or spatial memory (9 studies, comprising 206 subjects; g = 0.75, 95% confidence interval (CI) - 1.09 to 2.58, p = 0.43). However, acute, full CB1R agonists significantly impaired non-spatial memory (N = 23 studies, 519 subjects; g = - 1.39, 95% CI - 2.72 to - 0.06, p = 0.03). By contrast, the chronic administration of CB1R agonists had no effect on non-spatial memory (N = 5 studies, comprising 146 subjects; g = - 0.05, 95% confidence interval (CI) - 1.32 to 1.22, p = 0.94). Moreover, the acute administration of CB1R antagonists had no effect on non-spatial memory in rodents (N = 9 studies, N = 149 subjects; g = 0.40, 95% CI - 0.11 to 0.92, p = 0.12).

CONCLUSIONS

The acute administration of THC, partial CB1R agonist, significantly impaired non-spatial memory in humans, monkeys, and non-human primates but not rodents. However, full CB1R agonists significantly impaired non-spatial memory in a dose-dependent manner but CB1R antagonists had no effect on non-spatial memory in rodents. Moreover, chronic THC administration did not significantly impair spatial or non-spatial memory in rodents, and there is inconclusive evidence on this in humans. Our findings highlight species differences in the effects of cannabinoid compounds on memory.

Age, period and cohort effects in frequent cannabis use among US students: 1991-2018

BACKGROUND AND AIMS

As the legal status of cannabis changes across the United States and modes of administration expand, it is important to examine the potential impact on adolescent cannabis use. This study aimed to assess changes in prevalence of frequent cannabis use in adolescents in the United States and how far this varies by age and cohort.

DESIGN

Analysis of Monitoring the Future, a nationally representative annual survey of 8th-, 10th- and 12th-grade students in the United States conducted from 1991 to 2018.

SETTING

In-school surveys completed by US adolescents.

PARTICIPANTS

A total of 1 236 159 8th-, 10th- and 12th-graders; 51.5% female, 59.6% non-Hispanic white, 12.3% non-Hispanic black, 13.4% Hispanic and 14.7% other race/ethnicity.

MEASUREMENTS

Frequent cannabis use (FCU), defined as six or more occasions in the past 30 days, stratified by sex, race/ethnicity and parental education.

FINDINGS

FCU among US adolescents increased over the study period; the peak in 2010-18 was 11.4% among 18-year-old students. This increase was best explained by both period and cohort effects. Compared with respondents in 2005, adolescents surveyed in 2018 had period effects in FCU that were 1.6 times greater. Adolescents in younger birth cohorts (those born > 1988) had a lower increase in FCU than those born prior to 1988. Results were consistent across sex, parent education and race/ethnicity, with period effects indicating increasing FCU after 2005 and cohort effects indicating a lower magnitude of increase in more recent birth cohorts. Age and parental education disparities in FCU have increased over time, whereas race/ethnicity differences have converged over time; black students were 0.67 [95% confidence interval (CI) = 0.64-0.70] times as likely to use cannabis frequently as white students from 1991 to 2000, and 1.03 (95% CI = 0.98-1.09) times as likely from 2011 to 2018 (P-value for time interaction < 0.001).

CONCLUSIONS

The prevalence of frequent cannabis use (FCU) increased from 1991 to 2018 among older adolescents in the United States. Racial/ethnic differences in FCU converged, whereas parental education differences have diverged.

Marijuana use associated with worse verbal learning and delayed recall in a sample of young adults

BACKGROUND

There is concern about the cognitive consequences of marijuana consumption.

AIM

To assess the influence of current and past marijuana use and frequency on verbal learning and memory in a sample of adults aged 21 years old.

MATERIAL AND METHODS

Marijuana use was assessed using a clinician administered interview in 654 participants (56% females), who reported frequency of use, age of first use and whether its use led to problems in their lives. The CogState International Shopping List was administered to assess learning and memory.

RESULTS

Seventy percent reported ever using marijuana, 46% consuming during the past year and 27% during the past 30 days. The latter scored significantly lower on delayed recall. Current and frequent use were significantly associated with lower accuracy in verbal learning and memory.

CONCLUSIONS

In this cohort of adults aged 21 years old, marijuana use was prevalent and related to worse verbal memory.

College degree attainment by age of first marijuana use and parental education

Background: Age of first marijuana use is a key predictor of later educational outcomes, but limited work has identified demographic factors that impact this association across continuous ages of first use. The purpose of this study was threefold: (1) to identify the age-varying prevalence of later college degree attainment as a function of age of first marijuana use; (2) to examine the age-varying association of gender and college degree attainment as a function of age of first use; and (3) to examine the age-varying association of parent education and college degree attainment as a function of age of first use. Methods: Data were from the panel portion of the Monitoring the Future (MTF) study, an ongoing longitudinal study of adolescents and young adults. Those who used marijuana by age 22 were included in analyses. Among these participants (N = 2134), 47.0% were male, 67.5% were white, 53.2% reported having at least one parent with a bachelor's degree or higher, and 44.1% attained a bachelor's degree or higher by age 25/26. Results: Intercept-only and logistic time-varying effect models (TVEMs) modeled prevalences and associations as functions of age of first marijuana use. Prevalence of college degree completion was relatively linear across age of first use; such that college degree attainment increased as age of first use increased. Results indicated that college degree attainment varied across age of first use similarly for men and women. Degree attainment differences existed based on parent education. Parental education and degree attainment were most strongly linked at an age of first use between 16 and 19 years. Conclusions: Findings suggest that age of first marijuana use has an association with academic achievement such that earlier ages of first use are associated with lower academic achievement later in adulthood. Parental education serves as a protective factor against college degree attainment in late adolescence.

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

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.

The initiation of cannabis use in adolescence is predicted by sex-specific psychosocial and neurobiological features

Cannabis use initiated during adolescence might precipitate negative consequences in adulthood. Thus, predicting adolescent cannabis use prior to any exposure will inform the aetiology of substance abuse by disentangling predictors from consequences of use. In this prediction study, data were drawn from the IMAGEN sample, a longitudinal study of adolescence. All selected participants (n = 1,581) were cannabis-naïve at age 14. Those reporting any cannabis use (out of six ordinal use levels) by age 16 were included in the outcome group (N = 365, males n = 207). Cannabis-naïve participants at age 14 and 16 were included in the comparison group (N = 1,216, males n = 538). Psychosocial, brain and genetic features were measured at age 14 prior to any exposure. Cross-validated regularized logistic regressions for each use level by sex were used to perform feature selection and obtain prediction error statistics on independent observations. Predictors were probed for sex- and drug-specificity using post-hoc logistic regressions. Models reliably predicted use as indicated by satisfactory prediction error statistics, and contained psychosocial features common to both sexes. However, males and females exhibited distinct brain predictors that failed to predict use in the opposite sex or predict binge drinking in independent samples of same-sex participants. Collapsed across sex, genetic variation on catecholamine and opioid receptors marginally predicted use. Using machine learning techniques applied to a large multimodal dataset, we identified a risk profile containing psychosocial and sex-specific brain prognostic markers, which were likely to precede and influence cannabis initiation.

Prevalence and Sociodemographic Correlates of Adolescent Use and Polyuse of Combustible, Vaporized, and Edible Cannabis Products

IMPORTANCE

Cannabis legalization and commercialization have introduced novel alternative cannabis products, including edible and vaporized cannabis that might appeal to youth and be associated with polyuse (ie, use of ≥2 different products).

OBJECTIVE

To investigate the prevalence, patterns, and sociodemographic correlates of cannabis product use across combustible, edible, and vaporized administration methods, including polyuse of cannabis via multiple administration methods.

DESIGN, SETTING, AND PARTICIPANTS

This cross-sectional survey study included 10th-grade students from 10 Los Angeles, California, area high schools from January 2 through October 6, 2015. Students were recruited from respondents in the Happiness and Health Study, an ongoing prospective cohort study in the 10 high schools. Students not in school during administration of the pencil-and-paper survey completed abbreviated surveys by telephone, internet, or mail. Data were analyzed from July 17, 2017, through July 12, 2018.

EXPOSURES

Self-reported sex, race/ethnicity, and socioeconomic status (SES). Students with high SES had parents who attained college or a higher educational level and were ineligible for free or subsidized lunch; those with low SES had parents with lower educational attainment or were eligible for free or subsidized lunch.

MAIN OUTCOMES AND MEASURES

Self-report of ever use (yes or no) and past 30-day use (yes or no) status and frequency of use (days in past 30 days) of combustible, edible, and vaporized cannabis.

RESULTS

The sample included 3177 tenth-grade students (93.5% of study enrollees); among these students, 1715 (54.0%) were girls and the mean (SD) age was 16.1 (0.4) years. Among those with available demographic data, respondents were diverse in race/ethnicity (537 [17.2%] Asian; 149 [4.8%] black; 1510 [48.3%] Hispanic; 507 [16.2%] white; 207 [6.6%] multiethnic/multiracial; and 216 [6.9%] other) and included 1654 (60.1%) with a low SES. Prevalence of ever use was highest for combustible products (993 [31.3%]), followed by edible (676 [21.3%]) and vaporized (333 [10.5%]) products. A similar pattern was found for past 30-day use (426 [13.4%] for combustible, 249 [7.8%] for edible, and 156 [4.9%] for vaporized cannabis). Among participants who reported using cannabis in the past 30 days, mean frequency of use of combustible cannabis was higher by 2.65 days (95% CI, 1.40-3.91 days, P = .001) than the mean frequency of use for edible cannabis and 1.75 days higher (95% CI, 0.59-2.90 days, P = .003) than frequency of use for vaporized cannabis. Most cannabis users (665 [61.7%]) used multiple administration methods, and 260 (8.2%) used all 3 methods. Boys had higher prevalence of ever use for vaporized (170 [11.6%] vs 163 [9.5%]) but not combustible (459 [31.4%] vs 534 [31.1%]) or edible (303 [20.7%] vs 373 [21.7%]) cannabis. Respondents with low SES had higher prevalence of ever use for combustible (614 [37.1%] vs 242 [22.0%]) and edible (408 [24.7%] vs 166 [15.1%]) but not vaporized (186 [11.2%] vs 93 [8.5%]) cannabis.

CONCLUSIONS AND RELEVANCE

Among 10th-grade students in Los Angeles, use of cannabis via alternative administration methods was of appreciable prevalence, predominately reported in conjunction with other cannabis products and unequally distributed across sociodemographic strata. Prevention programs and regulatory restrictions addressing the spectrum of cannabis products might benefit pediatric public health.

Verbal Memory Performance and Reduced Cortical Thickness of Brain Regions Along the Uncinate Fasciculus in Young Adult Cannabis Users

Introduction: Memory impairment is one of the most commonly reported effects of cannabis use, especially among those who initiate use earlier, perhaps due to the effects of delta-9- tetrahydrocannabinol on cannabinoid (CB1) receptors in the brain. Studies have increasingly investigated whether cannabis use is associated with impairments in verbal memory, and with alterations in brain structures underlying verbal memory. The uncinate fasciculus (UF), a long-range white matter tract, connects regions with densely localized CB1 receptors that are important in verbal memory. This study investigated the impact of cannabis use on UF structures and its association with memory performance in young adult cannabis users (CU) and non-using controls (CON).

Materials and Methods: Nineteen CU and 22 CON completed a verbal memory task and a neuroimaging protocol, in which diffusion tensor imaging and structural scans were collected. We compared memory performance, diffusion and tractography measures of the UF, and cortical thickness of regions connected by the UF, between CU and CON. In regions showing a significant group effect, we also examined associations between verbal memory performance, cortical thickness, and age of onset of cannabis use.

Results: Compared to non-users, CU had worse memory performance, decreased fiber bundle length in the UF, and decreased cortical thickness of brain regions along the UF such as the entorhinal cortex and fusiform gyrus. Verbal memory performance was significantly associated with age of onset of cannabis use, indicating that those who initiated cannabis use at an earlier age performed worse. Cortical thickness of the entorhinal cortex was significantly correlated with age of first use and memory performance.

Conclusion: This study provides evidence that cannabis use, especially when initiated at a young age, may be associated with worse verbal memory and altered neural development along the UF. Reductions in cortical thickness in regions implicated in memory processes may underlie weaknesses in verbal memory performance.

The Grass Might Be Greener: Medical Marijuana Patients Exhibit Altered Brain Activity and Improved Executive Function after 3 Months of Treatment

The vast majority of states have enacted full or partial medical marijuana (MMJ) programs, causing the number of patients seeking certification for MMJ use to increase dramatically in recent years. Despite increased use of MMJ across the nation, no studies thus far have examined the specific impact of MMJ on cognitive function and related brain activation. In the present study, MMJ patients seeking treatment for a variety of documented medical conditions were assessed prior to initiating MMJ treatment and after 3 months of treatment as part of a larger longitudinal study. In order to examine the effect of MMJ treatment on task-related brain activation, MMJ patients completed the Multi-Source Interference Test (MSIT) while undergoing functional magnetic resonance imaging (fMRI). We also collected data regarding conventional medication use, clinical state, and health-related measures at each visit. Following 3 months of treatment, MMJ patients demonstrated improved task performance accompanied by changes in brain activation patterns within the cingulate cortex and frontal regions. Interestingly, after MMJ treatment, brain activation patterns appeared more similar to those exhibited by healthy controls from previous studies than at pre-treatment, suggestive of a potential normalization of brain function relative to baseline. These findings suggest that MMJ use may result in different effects relative to recreational marijuana (MJ) use, as recreational consumers have been shown to exhibit decrements in task performance accompanied by altered brain activation. Moreover, patients in the current study also reported improvements in clinical state and health-related measures as well as notable decreases in prescription medication use, particularly opioids and benzodiapezines after 3 months of treatment. Further research is needed to clarify the specific neurobiologic impact, clinical efficacy, and unique effects of MMJ for a range of indications and how it compares to recreational MJ use.

ELSA 2016 Cohort: Alcohol, Tobacco, and Marijuana Use and Their Association with Age of Drug Use Onset, Risk Perception, and Social Norms in Argentinean College Freshmen

The transition from high school to college is a high-risk stage for the initiation and escalation of substance use. Substance use and its associated risk factors have been thoroughly described in developed countries, such as the United States, but largely neglected in Argentina, a South American country with patterns of a collectivist culture. The present cross-sectional study describes the occurrence of alcohol, tobacco, and marijuana use and the association between these behaviors and the age of onset of substance use and cognitive (i.e., risk perception) and social (i.e., prescriptive) variables in a large sample of Argentinean college freshmen (n = 4083, 40.1% men; mean age = 19.39 ± 2.18 years). The response rate across courses was ≥90% and was similarly distributed across sex. Participants completed a survey that measured substance use (alcohol [with a focus on heavy drinking and binge drinking behaviors], tobacco, and marijuana), age of onset of the use of each substance, perceived risk associated with various substance use behaviors, prescriptive norms associated with substance use, and descriptive norms for alcohol use (AU). The results indicated that AU is nearly normative (90.4 and 80.3% with last year and last month use, respectively) in this population, and heavy drinking is highly prevalent (68.6 and 54.9% with heavy episodic and binge drinking, respectively), especially among those with an early drinking onset (97.8 and 93.6% with last year and last month use and 87.8 and 76.3% with heavy episodic and binge drinking, respectively). The last-year occurrence of tobacco and marijuana use was 36 and 28%, respectively. Early substance use was associated with the greater use of that specific substance. The students overestimated their same-sex friend's AU, and women overestimated the level of AU of their best male friend. At the multivariate level, all of the predictors, with the exception of the parents' prescriptive norms, significantly explained the frequency of marijuana and tobacco use and frequency of hazardous drinking. Overall, despite important cultural and contextual differences between Argentina and the United States, our findings suggest that certain vulnerability factors have a similar influence across these cultural contexts.

Splendor in the Grass? A Pilot Study Assessing the Impact of Medical Marijuana on Executive Function

Currently, 25 states and Washington DC have enacted full medical marijuana (MMJ) programs while 18 states allow limited access to MMJ products. Limited access states permit low (or zero) tetrahydrocannabinol (THC) and high cannabidiol (CBD) products to treat specified conditions such as uncontrolled epilepsy. Although MMJ products are derived from the same plant species as recreational MJ, they are often selected for their unique cannabinoid constituents and ratios, not typically sought by recreational users, which may impact neurocognitive outcomes. To date, few studies have investigated the potential impact of MMJ use on cognitive performance, despite a well-documented association between recreational marijuana (MJ) use and executive dysfunction. The current study assessed the impact of 3 months of MMJ treatment on executive function, exploring whether MMJ patients would experience improvement in cognitive functioning, perhaps related to primary symptom alleviation. As part of a larger longitudinal study, 24 patients certified for MMJ use completed baseline executive function assessments and 11 of these so far have returned for their first follow-up visit 3 months after initiating treatment. Results suggest that in general, MMJ patients experienced some improvement on measures of executive functioning, including the Stroop Color Word Test and Trail Making Test, mostly reflected as increased speed in completing tasks without a loss of accuracy. On self-report questionnaires, patients also indicated moderate improvements in clinical state, including reduced sleep disturbance, decreased symptoms of depression, attenuated impulsivity, and positive changes in some aspects of quality of life. Additionally, patients reported a notable decrease in their use of conventional pharmaceutical agents from baseline, with opiate use declining more than 42%. While intriguing, these findings are preliminary and warrant further investigation at additional time points and in larger sample sizes. Given the likelihood of increased MMJ use across the country, it is imperative to determine the potential impact of short- and long-term treatment on cognitive performance as well as the efficacy of MMJ treatment itself.