The effect of long-term chronic marijuana use on neuropsychological functioning

A longitudinal examination of the relationship between cannabis use and cognitive function in mid-life adults

BACKGROUND

The relationship between cannabis use and cognitive function in mid-life has rarely been examined despite verbal learning deficits in young adults.

METHOD

A longitudinal cohort study of 1,897 Australians recruited at 40-46 years of age and followed up 4 years (94%) and 8 years (87%) later. Random effects regression was used to assess within- and between-person associations between cannabis use and cognitive function across waves of data, and examine whether age-related changes in cognitive performance were modified by cannabis use. The first list of the California Verbal Learning Test (immediate and delayed recall), Symbol Digit Modality Test, Digit Backwards, simple and choice reaction time tasks, were administered at each wave. The Spot-the-Word test was used to assess premorbid verbal ability. Self-reported cannabis use in the past year (no use, < weekly use,≥weekly use) was assessed at each wave.

FINDINGS

Participants who used cannabis≥weekly had worse immediate recall (b=-0.68, p=0.014) and showed a trend toward worse delayed recall (b=-0.55, p=0.062) compared to non-users after adjusting for correlates of cannabis use and premorbid verbal ability. These effects were due to between-person differences. There were no significant within-person associations between cannabis use and recall, nor was there evidence of greater cognitive decline in cannabis users with age.

CONCLUSIONS

Mid-life cannabis users had poorer verbal recall than non-users, but this was not related to their current level of cannabis use, and cannabis use was not associated with accelerated cognitive decline.

Gone to Pot - A Review of the Association between Cannabis and Psychosis

Cannabis is the most commonly used illicit drug worldwide, with ~5 million daily users worldwide. Emerging evidence supports a number of associations between cannabis and psychosis/psychotic disorders, including schizophrenia. These associations-based on case-studies, surveys, epidemiological studies, and experimental studies indicate that cannabinoids can produce acute, transient effects; acute, persistent effects; and delayed, persistent effects that recapitulate the psychopathology and psychophysiology seen in schizophrenia. Acute exposure to both cannabis and synthetic cannabinoids (Spice/K2) can produce a full range of transient psychotomimetic symptoms, cognitive deficits, and psychophysiological abnormalities that bear a striking resemblance to symptoms of schizophrenia. In individuals with an established psychotic disorder, cannabinoids can exacerbate symptoms, trigger relapse, and have negative consequences on the course of the illness. Several factors appear to moderate these associations, including family history, genetic factors, history of childhood abuse, and the age at onset of cannabis use. Exposure to cannabinoids in adolescence confers a higher risk for psychosis outcomes in later life and the risk is dose-related. Individuals with polymorphisms of COMT and AKT1 genes may be at increased risk for psychotic disorders in association with cannabinoids, as are individuals with a family history of psychotic disorders or a history of childhood trauma. The relationship between cannabis and schizophrenia fulfills many but not all of the standard criteria for causality, including temporality, biological gradient, biological plausibility, experimental evidence, consistency, and coherence. At the present time, the evidence indicates that cannabis may be a component cause in the emergence of psychosis, and this warrants serious consideration from the point of view of public health policy.

Effects of cannabis on cognitive function in patients with multiple sclerosis

BACKGROUND

While neuropsychological deficits have been reported in healthy individuals who use street cannabis, data in patients with multiple sclerosis (MS) are lacking. Given that MS is associated with cognitive deterioration, the aim of this study was to determine the neuropsychological effects of cannabis use in this population.

METHODS

Two groups, each of 25 patients with MS (cannabis users and nonusers), were administered the Minimal Assessment of Cognitive Function in MS battery of neuropsychological tests, the Hospital Anxiety and Depression Scale (HADS), and the Structured Clinical Interview for the DSM-IV Axis I Disorders (SCID-I). Group-matching and regression analysis were used to control for the effects of age, sex, education, premorbid intelligence, disability, and disease course and duration on cognitive function.

RESULTS

Cannabis users performed significantly more poorly than nonusers on measures of information processing speed, working memory, executive functions, and visuospatial perception. They were also twice as likely as nonusers to be classified as globally cognitively impaired. There were no between-group differences on the HADS measures of depression and anxiety or lifetime SCID-I psychiatric diagnoses.

CONCLUSION

This cross-sectional study provides empirical evidence that prolonged use of inhaled or ingested street cannabis in patients with MS is associated with poorer performance on cognitive domains commonly affected in this population. Whatever subjective benefits patients may derive from using street cannabis (e.g., pain and spasticity relief) should be weighed against the associated cognitive side effects.

Abnormal cerebellar morphometry in abstinent adolescent marijuana users

Functional neuroimaging data from adults have, in general, revealed frontocerebellar dysfunction associated with acute and chronic marijuana (MJ) use. The goal of this study was to characterize cerebellar volume in adolescent chronic MJ users following 1 month of monitored abstinence. Participants were MJ users (n=16) and controls (n=16) aged 16-18 years. Extensive exclusionary criteria included history of psychiatric or neurologic disorders. Drug use history, neuropsychological data, and structural brain scans were collected after 28 days of monitored abstinence. Trained research staff defined cerebellar volumes (including three cerebellar vermis lobes and both cerebellar hemispheres) on high-resolution T1-weighted magnetic resonance images. Adolescent MJ users demonstrated significantly larger inferior posterior (lobules VIII-X) vermis volume than controls, above and beyond effects of lifetime alcohol and other drug use, gender, and intracranial volume. Larger vermis volumes were associated with poorer executive functioning. Following 1 month of abstinence, adolescent MJ users had significantly larger posterior cerebellar vermis volumes than non-using controls. These greater volumes are suggested to be pathological based on linkage to poorer executive functioning. Longitudinal studies are needed to examine typical cerebellar development during adolescence and the influence of marijuana use.

Acute and non-acute effects of cannabis on brain functioning and neuropsychological performance

Cannabis has an ancient history of human use and is currently one of the most commonly used drugs worldwide. Understanding its impact on neurobehavioral functioning is of significant public health concern. In recent decades, substantial progress has been made in understanding the impact of cannabis use on neurobehavioral functioning. This has been fueled, in part, by characterization of an endocannabinoid signaling system in the brain through which cannabis exerts its psychoactive effects. Acute intoxication with cannabis causes marked changes in subjective mental status, brain functioning, and neuropsychological performance. Some of these changes are consistently detected and well characterized, yet others are not. Changes in brain functioning and neuropsychological performance are also reported after abstinence, but appear to be mild, circumscribed, and transient. On the other hand, functional neuroimaging often reveals subtle differences in the brain functioning of abstinent cannabis users compared with controls. The persistence and clinical significance of these differences, however, remains to be determined. Neuropsychological deficits and differences in brain functioning are most consistently observed only among frequent, heavy users, who are those most likely addicted to cannabis. The dire impact of drug addiction on a person's life and everyday functioning suggests that the large number of individuals addicted to cannabis experience substantial negative effects from its use. This manuscript reviews the scientific literature on the aforementioned topics in detail, providing evidence for converging findings, and highlighting areas in need of further investigation.

Neuropsychological functioning in adolescent marijuana users: subtle deficits detectable after a month of abstinence

In adults, studies examining the long-lasting cognitive effects of marijuana use demonstrate subtle deficits in attention, executive function, and memory. Because neuromaturation continues through adolescence, these results cannot necessarily generalize to adolescent marijuana users. The goal of this study was to examine neuropsychological functioning in abstinent marijuana using and demographically similar control adolescents. Data were collected from 65 adolescent marijuana users (n=31, 26% females) and controls (n=34, 26% females) 16-18 years of age. Extensive exclusionary criteria included independent psychiatric, medical, and neurologic disorders. Neuropsychological assessments were conducted after>23 days of monitored abstinence. After controlling for lifetime alcohol use and depressive symptoms, adolescent marijuana users demonstrated slower psychomotor speed (p<.05), and poorer complex attention (p<.04), story memory (p<.04), and planning and sequencing ability (p<.001) compared with controls. Post hoc analysis revealed that the number of lifetime marijuana use episodes was associated with poorer cognitive function, even after controlling for lifetime alcohol use. The general pattern of results suggested that, even after a month of monitored abstinence, adolescent marijuana users demonstrate subtle neuropsychological deficits compared with nonusers. It is possible that frequent marijuana use during adolescence may negatively influence neuromaturation and cognitive development.

Nonacute (residual) neuropsychological effects of cannabis use: a qualitative analysis and systematic review

Because there is a possibility that cannabis or cannabis-like molecules might be used as treatments for certain conditions in the future, it becomes important to consider the possible adverse effects of these compounds. In this paper, the authors review the evidence for persisting effects of nonacute cannabis use on the central nervous system, as reflected by alteration in neuropsychological performance. From the 40 articles that met criteria for inclusion in this review, the authors could not detect consistent evidence for persisting neuropsychological deficits in cannabis users; however, 22 of the 40 studies reported at least some subtle impairments. The inability to reach a firm conclusion results largely from methodological limitations inherent in most studies. These are considered in detail to inform future studies on (nonacute) consequences of cannabis consumption on cognitive abilities.

Demographic effects on the Trail Making Test in marijuana abusers

Demographic effects on the Trail Making Test (TMT), a test often used for screening for cognitive impairment, were examined in a sample of marijuana abusers in drug abuse treatment programs. A sample was drawn from electronic files of data from the Drug Abuse Treatment outcome Study (DATOS). The DATOS was a naturalistic, prospective cohort study that collected data from 1991-1993 in 96 programs in 11 cities in the United States. The number of marijuana abusers' scores available for analysis were 259. Data were analyzed to determine the effects of sex, ethnicity, age, and education variables on the two parts of the TMT in this large treatment sample of marijuana abusers. The variables of age and education level were statistically significantly related to TMT parts A and B, and ethnicity was statistically significant for part B of the TMT. R-Square values for overall models were moderate (A = .15, B = .18) suggesting that demographic effects on the TMT are weak.

Personality profile and neuropsychological test performance in chronic cocaine-abusers

Little is known about the association between personality disorders and neuropsychological test performance in chronic cocaine users. The aims of the present study were to (1) pinpoint the specific neuropsychological characteristics of chronic cocaine abusers, (2) analyze their personality profile, and (3) explore the association between personality traits and neuropsychological test performance. A sample of 42 drug-abusers (mean age = 34.15; SD = 6.73; mean educational level = 11.44; SD = 2.01) was selected from a state rehabilitation facility and was compared to a control group (mean age = 34.53; SD = 9.01; mean educational level = 12.29; SD = 1.31). The following information was collected for each subject: (1) A clinical history adapted from Horton (1996). (2) The Personality Assessment Inventory (PAI) (Morey, 1991). (3) A neuropsychological test battery including: Arithmetic and Digits subtests from the WAIS-R, California Verbal Learning Test, Trial Making Test, Verbal Fluency tests, Rey-Osterrieth Complex Figure, Wisconsin Card Sorting Test, Benton Visual Retention Test, Stroop Neurological Screening Test and Hooper Visual Organization. Thirty-seven of the drug-dependent subjects obtained an abnormal score in at least one PAI scale. The personality profile of the drug-dependent subjects found via the PAI pointed to a Borderline/Antisocial personality, frequently associated with mania features. In six of the drug-abusers, a normal personality profile was observed. Neuropsychological test performance scores were within the low average or borderline range. The most abnormal scores were observed in attention, memory, and executive functioning tests. The results did not show any robust association between personality profile and neuropsychological test performance.

Beyond the theoretical rhetoric: a proposal to study the consequences of drug legalization

Drug legalization is a frequently-debated drug control policy alternative. It should come as little surprise, therefore, that the arguments in favor of both legalization and prohibition have resulted in a conceptual stalemate. While theoretical deliberations are unquestionably valuable, they seem to have propelled this particular issue to its limit. To date, no works have suggested any empirical studies that might test the framework and potential consequences of drug legalization. In the current study, the arguments surrounding the drug legalization debate are synthesized into a proposal for future research. Such a proposal illustrates that the core elements surrounding drug legalization are not only testable, but that the time may be right to consider such an empirical effort.

The relationship of neuropsychological functioning to measures of substance use in an adolescent drug abusing sample

The purpose of this research was to investigate the relationship between recent and long term substance use on adolescents' neuropsychological functioning. Subjects were 77 adolescents who were referred for outpatient treatment for drug and conduct problems. Subjects were administered the Luria-Nebraska Neuropsychological Battery-III, structured interviews to assess substance use, and urine tests. Subjects were divided into neuropsychologically impaired and nonimpaired groups. Results indicated no significant group differences for: self-reports of lifetime use of alcohol, cannabis, and hard drugs; self or collateral reports of recent (past 30 days) use of alcohol, cannabis, and hard drugs; or urinalysis detection of alcohol, cannabis, and hard drugs. Correlations between these dependent measures of substance use and neuropsychological functioning were also nonsignificant (all ps > .05). Although neuropsychological impairment was observed for some subjects in this sample, it was unrelated to their cannabis, hard drug, or alcohol use. These results are consistent with those found in the adult literature, given the relatively short period of time that these youth have used such substances. However, given the severity of their absolute levels of substance usage, they may be at greater risk for developing future neuropsychological problems, related directly to the ingestion of alcohol and illicit drugs, and to their secondary effects (e.g., head traumas, malnutrition).

Traumatic brain injury, depression and cannabis use--assessing their effects on a cognitive performance

Patient RB is presented as a demonstration of the need for a more thorough understanding of the interactions of patient variables. RB had a history of traumatic brain injury along with current mood disorder and cannabis use. It was unclear initially whether or not his cognitive impairment was a permanent result of the brain injury, or a temporary effect of his mood and/or drug use. The literature offers few guidelines or precedents for understanding such complex cases or suggesting at which level it may be most appropriate to intervene. The impact of cannabis use in this individual appeared to have a detrimental effect on his mood. Treating RB's mood disorder resulted in larger cognitive gains than would have been anticipated in the literature. Specific neuropsychological tests are identified as being particularly sensitive to the cognitive changes in mood disorders.

Marijuana and Job Performance: Comparing the Major Streams of Research

Though some estimate that marijuana use has cost U.S. companies billions of dollars in lost productivity, the relationship between use of marijuana and job performance is far from clear. In this paper, I review studies on this topic from four different methodological perspectives and discuss models to account for their apparently contradictory findings. This discussion suggests hypotheses for future research addressing possible reasons for inconsistencies in past findings.

Cognitive effects of cocaine and polydrug abuse

One hundred and eighty-three participants were divided into three groups containing: 61 cocaine-dependent; 59 polydrug-dependent; and 63 normal subjects. All were evaluated using a basic neuropsychological assessment battery. The dependent groups exhibited significantly lower scores on short-term memory, attention, and concept formation tests. Performance on some subtests correlated negatively with the length of dependency and frequency of substance use. As compared with the control group, the dependent groups exhibited significant differences in the following personal and family areas: (a) depression and anxiety traits; (b) self-aggression and lack of fear in childhood; (c) family history of substance dependency; and (d) difficulties with interpersonal relationships. The operation of predisposing developmental factors for substance dependence is suggested.

Cognitive impairments in adolescent drug-abusers

A basic neuropsychological test battery was given to 64 adolescents (57 males and seven females; mean age = 15.5) divided in two groups: (1) drug-abusers ("experimental group," n = 26), and (2) non drug-abusers ("control group," n = 38). Psychoactive substances included marijuana, "crack," solvent inhalation, gasoline sniffing, and alcohol. The following tests were used: (1) language, (2) perceptual recognition, (3) memory, and (4) praxic abilities. In general, performance was mildly (but nonsignificantly) lower in the experimental than in the control group. Only some neuropsychological test scores correlated with lifetime and amount of psychoactive drugs used. It was proposed that cognitive impairments in this sample of young drug-abusers may have been not evident because: (1) lifetime use was limited, due to the age of the subjects; and (2) in adolescents and pre-adolescents, toxic effects of drug-abuse might be manifested as a decrease in the rate of cognitive development rather than as a general cognitive decline.

Effects of chronic marijuana use on human cognition

Impairments of human cognition and learning following chronic marijuana use are of serious concern, but have not been clearly demonstrated. To determine whether such impairments occurred, this study compared performance of adult marijuana users and non-users (N = 144 and N = 72, respectively) matched on intellectual functioning before the onset of drug use, i.e., on scores from standardized tests administered during the fourth grade of grammar school (Iowa Tests of Basic Skills). Subjects were given the twelfth grade versions of these tests (Iowa Tests of Educational Development) and other, computerized cognitive tests in successive test sessions. "Heavy" marijuana use (defined by use seven or more times weekly) was associated with deficits in mathematical skills and verbal expression in the Iowa Tests of Educational Development and selective impairments in memory retrieval processes in Buschke's Test. The retrieval impairments were restricted to words that were easy to visualize. Impairments depended on the frequency of chronic marijuana use, i.e., "light" and "intermediate" marijuana use (defined by use one to four and five to six times weekly, respectively) were not associated with deficits. Intermediate use was associated with superior performance in one condition ("fuzzy" concepts) of a Concept Formation test.

Effects of long-term cannabis use on selective attention: an event-related potential study

Brain event-related potentials (ERPs) were recorded from nine long-term cannabis users during a complex auditory selective attention task and compared with nine nonuser controls. Stimuli consisted of a random sequence of tones varying in location, pitch and duration. Subjects were instructed to respond to long-duration tones of a particular pitch and location. Cannabis users' task performance was significantly worse than controls. The most striking difference between the ERPs of the two groups was in the greatly enhanced early processing negativity in the user group to short-duration stimuli which matched the target on location only. This is indicative of users engaging in unnecessary pitch processing and thus having difficulty in setting up an accurate focus of attention and in filtering out irrelevant information. The data suggest a dysfunction in the allocation of attentional resources and stimulus evaluation strategies. These results imply that long-term cannabis use may impair the ability to efficiently process information.

Neuropsychological deficits in chronic cocaine abusers

A basic neuropsychological assessment battery was given to thirty-seven chronic freebase cocaine ("crack") abusers. The following tests were used: Wechsler Memory Scale (Wechsler, 1945), Rey-Osterrieth Complex Figure (Osterrieth, 1944) (copy and immediate reproduction), Verbal Fluency (semantic and phonologic), Boston Naming Test (Goodglass, Kaplan, & Weintrab, 1983), Wisconsin Card Sorting Test (Heaton, 1981) and Digit-symbol from the WISC (Wechsler, 1974). In general, performance was lower than expected according to their age and educational level. Subjects showed significant impairment in short-term verbal memory and attention subtests. Neuropsychological test scores were correlated with lifetime amount of cocaine used, suggesting a direct relationship between cocaine abuse and cognitive impairment. A pattern of cognitive decline is proposed.

The chronic cerebral effects of cannabis use. I. Methodological issues and neurological findings

This paper examines the research evidence relating sustained use of marijuana to chronic cerebral impairment. Evidence from both American and cross-cultural studies is reviewed, with a particular emphasis on methodological problems in the research. The focus of this paper is on neurological findings while another paper focuses on neuropsychological findings. On the basis of available research, it was concluded that there is no evidence that marijuana produces gross structural cerebral changes and little evidence that it leads to functional impairment, although subtle impairment cannot be ruled out.

The chronic cerebral effects of cannabis use. II. Psychological findings and conclusions

This paper examines the research evidence on the question of whether sustained use of marijuana may produce chronic cerebral impairment as measured by neuropsychological measures. Evidence from both American and cross-cultural studies suggests that marijuana probably does not produce chronic cerebral impairment, although subtle impairment cannot be ruled out. Several suggestions for new lines of research are discussed including prospective studies, effects of cannabis use on later aging processes, and true experimental studies.