The Effects of Cannabis Use on Cognitive Function in Healthy Aging: A Systematic Scoping Review

The Use of Cannabis-Based Medicine in Selected Neurological Disorders

Cannabis-based medicine (CBM) is used in a wide variety of different neurological disorders. While the use of CBM in the treatment of pain, AIDS wasting, loss of appetite, and spasticity is well established, CBM application in movement disorders and neurodegenerative disorders is still an emerging topic. The purpose of this chapter is to summarize current evidence behind the use of CBM in selected neurological diseases, mainly movement and neurodegenerative disorders. The best evidence for efficacy of CBM is for Tourette syndrome resulting in an improvement of tics and psychiatric comorbidities. In this indication, delta-9-tetrahydrocannabinol (THC)-containing CBMs are recommended. There is limited evidence that CBMs are also effective in Parkinson's disease in which they may improve tremor, but also non-motor symptoms such as pain and sleeping problems. With respect to other neurodegenerative diseases, there is limited evidence that CBMs may improve behavioral symptoms in Huntington's disease. In addition, it has been speculated that CBMs may have neuroprotective effects, but this has not yet been confirmed in the clinical setting.

Lysosomal cholesterol accumulation in aged astrocytes impairs cholesterol delivery to neurons and can be rescued by cannabinoids

Cholesterol is crucial for the proper functioning of eukaryotic cells, especially neurons, which rely on cholesterol to maintain their complex structure and facilitate synaptic transmission. However, brain cells are isolated from peripheral cholesterol by the blood-brain barrier and mature neurons primarily uptake the cholesterol synthesized by astrocytes for proper function. This study aimed to investigate the effect of aging on cholesterol trafficking in astrocytes and its delivery to neurons. We found that aged astrocytes accumulated high levels of cholesterol in the lysosomal compartment, and this cholesterol buildup can be attributed to the simultaneous occurrence of two events: decreased levels of the ABCA1 transporter, which impairs ApoE-cholesterol export from astrocytes, and reduced expression of NPC1, which hinders cholesterol release from lysosomes. We show that these two events are accompanied by increased microR-33 in aged astrocytes, which targets ABCA1 and NPC1. In addition, we demonstrate that the microR-33 increase is triggered by oxidative stress, one of the hallmarks of aging. By coculture experiments, we show that cholesterol accumulation in astrocytes impairs the cholesterol delivery from astrocytes to neurons. Remarkably, we found that this altered transport of cholesterol could be alleviated through treatment with endocannabinoids as well as cannabidiol or CBD. Finally, according to data demonstrating that aged astrocytes develop an A1 phenotype, we found that cholesterol buildup is also observed in reactive C3+ astrocytes. Given that reduced neuronal cholesterol affects synaptic plasticity, the ability of cannabinoids to restore cholesterol transport from aged astrocytes to neurons holds significant implications in aging and inflammation.

Sex Differences in the Association Between Cumulative Use of Cannabis and Cognitive Function in Middle Age: The Coronary Artery Risk Development in Young Adults Study

Background: Cannabis use may impair cognitive function (CF) differently in men and women, due to sex-specific differences in neurobiological mechanisms and environmental risk factors. Objective: Assess sex differences in the association between cumulative exposure to cannabis and cognitive performance in middle age. Methods: We studied participants from the Coronary Artery Risk Development in Young Adults (CARDIA) Study, including Black and White men and women 18-30 years old at baseline followed over 30 years. Our cross-sectional analysis of CF scores at year 30 was stratified by sex. We computed categories of cumulative exposure in "cannabis-years" (1 cannabis-year=365 days of use) from self-reported use every 2 to 5 years over 30 years. At years 25 and 30, we assessed CF with the Rey Auditory Verbal Learning Test (verbal memory), the Digit Symbol Substitution Test (processing speed), and the Stroop Interference Test (executive function). At year 30, additional measures included Category and Letter Fluency Test (verbal ability) and the Montreal Cognitive Assessment (global cognition). We computed standardized scores for each cognitive test and applied multivariable adjusted linear regression models for self-reported cumulative cannabis use, excluding participants who used cannabis within 24 h. In a secondary analysis, we examined the association between changes in current cannabis use and changes in CF between years 25 and 30. Results: By year 30, 1,352 men and 1,793 women had measures of CF; 87% (N=1,171) men and 84% (N=1,502) women reported ever cannabis use. Men had a mean cumulative use of 2.57 cannabis-years and women 1.29 cannabis-years. Self-reported cumulative cannabis use was associated with worse verbal memory in men (e.g., -0.49 standardized units [SU] for ≥5 cannabis-years of exposure; 95% CI=-0.76 to -0.23), but not in women (SU=0.02; 95% CI=-0.26 to 0.29). Other measures of CF were not associated with cannabis. Changes in current cannabis use between years 25 and 30 were not associated with CF in men or women. Conclusions: Self-reported cumulative cannabis exposure was associated with worse verbal memory in men but not in women. Researchers should consider stratified analyses by sex when testing the association between cannabis and cognition.

Changes in modes of cannabis consumption pre- and post-legalization and their correlates among adults in Ontario, Canada: 2017-2022

Background: Despite an increase in the varieties of cannabis products available for consumption, limited evidence is available about the patterns of cannabis consumption methods before and after legalization.Objectives: To examine the changes in modes of cannabis use and their correlates among adults in Ontario, Canada both prior to and following cannabis legalization in 2018.Methods: Data were utilized from the 2017 to 2022 Centre for Addiction and Mental Health's (CAMH) Monitor study, a repeated cross-sectional survey of adults 18 years of age and older (n = 2,665; 56% male). The surveys employed a regionally stratified sampling design using computer-assisted telephone interviews and web surveys. Multinomial regression was performed to examine different modes of cannabis use.Results: The exclusive use of cannabis through ingestion methods increased from 4.0% in 2017 to 16.6% in 2022 (p < .001). However, the exclusive use of inhalation-based cannabis decreased from 49.4% in 2017 to 25.5% in 2022 (p < .001). Relative to inhalation-based modes, adults were about five times more likely to use ingestion-based modes in 2020 [RRR = 4.65 (2.94-7.35)] and 2022 [RRR = 4.75 (2.99-7.55)] than in 2019, after accounting for sociodemographic factors.Conclusions: Ingestion-based cannabis use among adults increased fourfold between 2017 and 2022, a period during which recreational cannabis use was legalized in Canada. The increase was especially evident after the legalization of cannabis edibles.

The Impact of Cannabis Use on Cognition in People with HIV: Evidence of Function-Dependent Effects and Mechanisms from Clinical and Preclinical Studies

PURPOSE OF REVIEW

Cannabis may have beneficial anti-inflammatory effects in people with HIV (PWH); however, given this population's high burden of persisting neurocognitive impairment (NCI), clinicians are concerned they may be particularly vulnerable to the deleterious effects of cannabis on cognition. Here, we present a systematic scoping review of clinical and preclinical studies evaluating the effects of cannabinoid exposure on cognition in HIV.

RECENT FINDINGS

Results revealed little evidence to support a harmful impact of cannabis use on cognition in HIV, with few eligible preclinical data existing. Furthermore, the beneficial/harmful effects of cannabis use observed on cognition were function-dependent and confounded by several factors (e.g., age, frequency of use). Results are discussed alongside potential mechanisms of cannabis effects on cognition in HIV (e.g., anti-inflammatory), and considerations are outlined for screening PWH that may benefit from cannabis interventions. We further highlight the value of accelerating research discoveries in this area by utilizing translatable cross-species tasks to facilitate comparisons across human and animal work.

Characteristics of Cannabis and Opioid Users Among Older U.S. Veterans and Their Health Outcomes: A Longitudinal Perspective

Medical cannabis use among U.S. Veterans has continued to rise. However, data on cannabis use by older Veterans is generally less available. This study aims to understand the characteristics of older Veterans who enrolled in the Medical Cannabis Patient Program in Illinois and analyze their health outcomes and co-use of cannabis and opioids using longitudinal survey data. Overall, participants reported positive outcomes for pain, sleep, and emotional problems because of cannabis use in two survey periods. Approximately, 62% and 85% respondents reported no change in memory and falls, respectively, with only 3% and 1% reporting a negative outcome for the conditions in both surveys. About 20.4% of those who indicated cannabis use only in the initial survey started to co-use opioids in the follow-up survey, while 44.1% of those who indicated the use of both substances in the initial survey reported no longer using opioids in the follow-up survey. However, these changes were not statistically significant (α = 0.05 ) . The logistic regression showed that both clinical and contextual factors affected co-use. In conclusion, older U.S. Veterans may be using cannabis to alleviate their pain and other chronic conditions. More research is needed to understand the effect of cannabis use on reducing or substituting opioids.

The Role of Cannabis and The Endocannabinoid System in Sleep Regulation and Cognition: A Review of Human and Animal Studies

OBJECTIVES

Both sleep and cognition are partially modulated by the endocannabinoid (ECB) system. Cannabis has been reported to have effects on sleep and cognition. This review aims to summarize the recent literature on the ECB system, the role of cannabis and the ECB system on sleep regulation and cognition. Further, this review will identify existing gaps in knowledge and suggest potential targets for future research.

METHODS

We performed this review in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Reports were identified by searching PubMed/MEDLINE, Embase, CINAHL, Web of Science, and PsycINFO for articles published through September 2021 for studies with data available on aspects of cognition, cannabis, or the ECB system, and sleep or circadian rhythms (CRs).

RESULTS

We identified 6 human and 6 animal studies to be eligible for inclusion in this review. Several human studies found that cannabis use is not associated with changes in sleep quality or cognitive function. However, individual cannabinoids appeared to have independent effects on cognition and sleep; THC alone decreased cognitive performance and increased daytime sleepiness, whereas CBD alone had no effect on sleep or cognition. Animal studies demonstrated that manipulation of the ECB system altered activity and cognitive function, some of which appeared to be dependent on the light/dark cycle.

CONCLUSION

The sleep-wake cycle and CRs are both likely modulated by the ECB system, potentially resulting in effects on cognition, however this area is critically understudied.

Association Between Cannabis Use and Subjective Cognitive Decline: Findings from the Behavioral Risk Factor Surveillance System (BRFSS)

BACKGROUND

Cannabis consumption has rapidly increased in the United States due to more states legalizing non-medical and medical use. There is limited research, however, investigating whether cannabis may be associated with cognitive function, particularly across multiple dimensions of cannabis use.

OBJECTIVE

The objective of this study was to examine whether cannabis consumption reason, frequency, and method are associated with subjective cognitive decline (SCD).

METHODS

Data were obtained from 4,744 U.S. adults aged 45 and older in the 2021 Behavioral Risk Factor Surveillance System (BRFSS). SCD was a self-reported increase in confusion or memory loss in the past year. Odds of SCD by cannabis use reason, frequency, and methods (e.g., smoke, eat, vaporize) were examined using multiple logistic regression after imputing missing data, applying sampling weights, and adjusting for sociodemographic, health, and substance use covariates.

RESULTS

Compared to non-users, non-medical cannabis use was significantly associated with 96% decreased odds of SCD (aOR=0.04, 95% CI=0.01-0.44, p<.01). Medical (aOR=0.46, 95% CI=0.06-3.61, p=.46) and dual medical and non-medical use (aOR=0.30, 95% CI=0.03-2.92, p=.30) were also associated with decreased odds of SCD, although not significant. Cannabis consumption frequency and method were not significantly associated with SCD.

CONCLUSION

The reason for cannabis use, but not frequency and method, is associated with SCD. Further research is needed to investigate the mechanisms that may contribute to the observed associations between non-medical cannabis use and decreased odds of SCD.

Evidence on the acute and residual neurocognitive effects of cannabis use in adolescents and adults: a systematic meta-review of meta-analyses

BACKGROUND

Cannabis is among the most consumed psychoactive substances world-wide. Considering changing policy trends regarding the substance, it is crucial to understand more clearly its potential acute and residual adverse effects from a public health viewpoint. Cognitive function is one of the targeted areas with conflicting findings. This meta-review measured the magnitude of acute and residual effects of cannabis on cognition in adolescents and adults provided by meta-analyses and evaluated quality of evidence.

METHODS

A systematic search was performed in PubMed, PsycINFO, Web of Science and Google Scholar. Meta-analyses were included if they quantitatively examined the performances of users from the general population on cognitive tasks.

RESULTS

The search retrieved 10 eligible meta-analyses (71 effects sizes, n = 43 761) with evidence ranging from low to moderate quality, which were categorized into domains of cognitive functions: executive functions (k = 7), learning and memory (k = 5), attention (k = 4), processing speed (k = 5), perceptual motor function (k = 2) and language (k = 2). Verbal learning and memory displayed the most robust evidence and were most impaired by acute cannabis intoxication that persisted after intoxication passed. Small-to-moderate acute and residual   adverse effects were reported for executive functioning. Cannabis use led to small deficits in inhibitory processes and flexibility, whereas small-to-moderate deficits were reported for working memory and decision-making. Evidence regarding processing speed and attention has shown that cannabis administration induced small-to-moderate adverse effects and residual neurocognitive deficits were observed in heavy cannabis-using youths. Results showed no significant difference between cannabis users and non-users on language, and small-to-moderate effects for simple motor skills.

CONCLUSION

Meta-analytical data on the acute effects of cannabis use on neurocognitive function have shown that cannabis intoxication leads to small to moderate deficits in several cognitive domains. These acute impairments accord with documented residual effects, suggesting that the detrimental effects of cannabis persist beyond acute intake.

Differences in Inhibitory Control and Resting Brain Metabolism between Older Chronic Users of Tetrahydrocannabinol (THC) or Cannabidiol (CBD)—A Pilot Study

Δ9-Tetrahydrocannabinol is the main psychoactive component of cannabis and cannabidiol is purportedly responsible for many of the medicinal benefits. The effects of Δ9-tetrahydrocannabinol and cannabidiol in younger populations have been well studied; however, motor function, cognitive function, and cerebral glucose metabolism in older adults have not been extensively researched. The purpose of this study was to assess differences in cognitive function, motor function, and cerebral glucose metabolism (assessed via [¹⁸F]-fluorodeoxyglucose positron emission tomography) in older adults chronically using Δ9-tetrahydrocannabinol, cannabidiol, and non-using controls. Eight Δ9-tetrahydrocannabinol users (59.3 ± 5.7 years), five cannabidiol users (54.6 ± 2.1 years), and 16 non-users (58.2 ± 16.9 years) participated. Subjects underwent resting scans and performed cognitive testing (reaction time, Flanker Inhibitory Control and Attention Test), motor testing (hand/arm function, gait), and balance testing. Δ9-tetrahydrocannabinol users performed worse than both cannabidiol users and non-users on the Flanker Test but were similar on all other cognitive and motor tasks. Δ9-tetrahydrocannabinol users also had lower global metabolism and relative hypermetabolism in the bilateral amygdala, cerebellum, and brainstem. Chronic use of Δ9-tetrahydrocannabinol in older adults might negatively influence inhibitory control and alter brain activity. Future longitudinal studies with larger sample sizes investigating multiple Δ9-tetrahydrocannabinol:cannabidiol ratios on functional outcomes and cerebral glucose metabolism in older adults are necessary.

Cannabis and Prescription Drug Use Among Older Adults With Functional Impairment

INTRODUCTION

Psychoactive substance use may be risky for adults with functional impairments. This study investigates cannabis use and prescription opioid and tranquilizer/sedative (mis)use among adults aged ≥50 years reporting functional impairments in the U.S.

METHODS

This cross-sectional analysis of adults aged ≥50 years from the 2015-2019 cohorts of the National Survey on Drug Use and Health estimates the prevalence of past-year medical and nonmedical cannabis use and prescription opioid and tranquilizer/sedative use and misuse according to the number of functional impairments reported. The adjusted odds of medical and nonmedical use or misuse of each substance in relation to any impairment, the number of impairments, and specific impairments were estimated using logistic regression. Analyses were conducted in December 2020.

RESULTS

Compared with those reporting no impairments, those reporting any impairment were more likely to report the use of cannabis and the (mis)use of prescription opioids and tranquilizers/sedatives (all p<0.05). Prevalence of (mis)use increased for each drug as the number of impairments increased (all p<0.001). Having any impairment was associated with increased odds for medical cannabis use (AOR=2.28, 95% CI=1.57, 3.30) but not for nonmedical use and with increased odds for misuse of prescription opioids (AOR=1.62, 95% CI=1.38, 1.91) and tranquilizers/sedatives (AOR=1.59, 95% CI=1.20, 2.11). Impaired thinking was associated with increased odds for the use and misuse of each substance, and impaired ability to do errands was associated with increased odds for prescription opioid misuse (AOR=1.34, 95% CI=1.01, 1.78).

CONCLUSIONS

Prescription drug misuse is linked to functional impairments among adults aged ≥50 years and may pose a potential risk for this vulnerable population.