Psychological Reports, 1990, 67, 947-952.
O Psychological Reports 1990
MENTAL PERFORMANCE IN LONG-TERM HEAVY CANNABIS USE: A PRELIMINARY REPORT '
Human Cognitive Neuropsychology Laboratory Universig of Seville, Spain Summary.-Mental performance of 23 male chronic cannabis users was measured on the 1958 Wechsler Adult Intelligence Scale and compared with scores of a control group. Analysis showed significant differences on nine of the 14 scores especially those indicating capacity for compromise, the elaboration of adequate judgments, and the capacity of verbalization and communjcation.
Various authors have reported that acute consumption as well as chronic consumption of cannabis derivatives affects behavior and thinking or judgment (Stone, 1973). Individuals with personal psychopathological antecedents are more vulnerable to the disintegration of the personahty than others (Mandell & Geyer, 1980). The acute consumption of such substances provokes mood changes, usually euphoric, alterations of the meaning of the time and visual or auditory perception, and in high doses, depersonalization and derealization (Isbell, Gorodetsky, Jasinski, Claussen, Spulak, & Korte, 1967). Clark (1968) reported acute consumption produces deterioration of complex reaction time and memory for digits. Weil, Zinberg, and Nelsen (1968) stated that consumption intoxicated mildly, and in a later analysis they indicated that individuals high on marijuana have subtle difficulties in speech; use of this substance interferes with retrieval of information from memory (Weil & Zinberg, 1969). A temporal disintegration and deterioration of immediate memory was observed by Melges, Tinklenberg, Hollister, and Gillespie (1970). Acute consumption decreased motor performance significantly (Manno, Kiplinger, Haine, Bennett, & Forney, 1970). According to Abel (1971), cannabis even produced interference in learning processes because its derivatives affect acquisition processes that contribute to the storage of information although these substances do not apparently affect the recovery of information from memory. When free recall is used, however, the recognition processes are affected. Dornbush, Fink, and Freedman (1971) support the results obtained on memory: marijuana affects short-term memory and reaction time. Chronic consumption of cannabis derivatives has also been stuhed. One 'Preparation of this paper was supported by the Consejerla de Educacibn y Ciencia (Junta de Andalucla) Consolidaci6n de Grupos de Investigaci6n y Desarrollo Tecnol6gico (BOJA 15/8/90). Requests for reprints should be sent to JosC Le6n-Carribn, Departamento de Psicologia Evolutiva y de la Educacibn, Bhsica y Metodologia, Universidad de Sev~Ua,Avda. San Francisco Javier s/n, 41005 Sevilla, Spain.
of the first reports by Soueif (1967) in Egypt indicated that the users of this drug showed alterations in memory and thought throughout a conversation. These results coincided with observations made later by Mendhiratta, Wigg, and Verma (1978) that the users of these drugs suffered from motor-perceptive disorders, deterioration of memory, and difficulties in concentration. The possibility that chronic consumption of cannabis produces cerebral damage has also been noted by several authors (Campbell, Evans, Thomson, & Williams, 1971; Kolansky & Moore, 1972); although Tulving, Thuling, Risberg, and Warkentin (1986), in studying regional cerebral blood flow in long-term heavy cannabis users, found no significant abnormalities in flow. The global CBF reduction seen in the early phase of detoxification is most likely the consequence of the dysfunction in the central nervous system accompanying chronic cannabis use. Moreover, Lebn-Carribn and Vela-Bueno (1990) found that chronic consumption of these substances can affect cognitive styles and the brain, altering the Basic Rest Activity Cycle between the cerebral hemispheres. The study described here concerns how chronic consumption of cannabis derivatives affects mental execution and intellectual skdls, focussing on heavy users who have never been diagnosed or treated for psychiatric problems and appear to function normally in their social community.
Subjects
To carry out this study we tested a group of cannabis users and a control group. The criteria for belonging to the cannabis group were that each was a regular smoker or user of cannabis derivatives (hashish), male, in the age range between 18 and 27 yr., with more than six mo. of daily consumption, right lateral dominance, no consumption of other drugs, no personal or family psychopathological antecedents, education below the last year of high school in Spain, preferably employed or unemployed workers, who had the same socioeconomic and cultural status, i.e., they all were friends and lived on the same street in the same neighbourhood, and had no left-handed family members. The control group had basically the same characteristics except for the fact that they had never smoked or used cannabis. The mean consumption rate of smokers was 2.5 cigarettes daily, and the mean length of consumption was 4.5 yr. From a sample of 181 individuals 45 subjects were selected and agreed to take part, 23 for the cannabis group and 24 for the control group. For various reasons such as previous psychopathology, use of other drugs, etc. 134 were excluded. Procedure
The Wechsler Adult Intelligence Scale (WAIS) was administered accord-
CANNABIS USE AND MENTAL PERFORMANCE
949
ing to the instructions for administration, assessment, and interpretation proposed by Wechsler (1958). All subjects were administered a questionnaire about drug use, a questionnaire on psychopathology, a clinical interview, and the Lateral Dominance Examination of the Halstead-Reitan Neuropsychological Test Battery. The means and standard deviations for each variable for each group were calculated, and the significance of differences between group means were estimated by Student's t.
The means and standard deviations for all WAIS measures by the control group and the smokers' group are given in Table 1. Analysis indicated significant differences between the two groups on nine of the 14 variables. TABLE 1 MEANSAND STANDARD DEVIATIONS FOR23 CANNABIS SMOKERSA N D 24 CONTROL SL~ECTS
WAIS Subscales
Cannabis M SD
Control M
t
P
SD
Information Comprehension
Arithmedc Similarities Digit Span
Vocabulary Digit Symbol Picture Completion Block Design Picture Arrangement Object Assembly Verbal IQ Performance IQ F d Scale IQ
Cannabis users showed that total IQ was lower than that of nonusers (t = 9.75, p < ,001) and that Verbal IQ and the Performance IQ were much lower (t = 8.21, p > ,001 and t = 7.68, p < .001, respectively). The largest significant difference between the groups on the different subtests of the test can be seen on Comprehension, on which the smokers obtained a lower score than the control group (t= 9.13, p < .001). We also observed that the group of hashish users obtained a lower score than was expected for their age, which could be understood as a pathological sign because, according to the general manual for the whole test, they should have obtained higher scores. Vocabulary and Object Assembly are the other subtests on which significantly lower scores were noted for smokers (t = 4.01, p < .001 and t = 3.98, p < .OO1, respectively).
O n six of the 14 WAIS measurements cannabis users showed lower mean scores than the control group (p
O Psychological Reports 1990
MENTAL PERFORMANCE IN LONG-TERM HEAVY CANNABIS USE: A PRELIMINARY REPORT '
Human Cognitive Neuropsychology Laboratory Universig of Seville, Spain Summary.-Mental performance of 23 male chronic cannabis users was measured on the 1958 Wechsler Adult Intelligence Scale and compared with scores of a control group. Analysis showed significant differences on nine of the 14 scores especially those indicating capacity for compromise, the elaboration of adequate judgments, and the capacity of verbalization and communjcation.
Various authors have reported that acute consumption as well as chronic consumption of cannabis derivatives affects behavior and thinking or judgment (Stone, 1973). Individuals with personal psychopathological antecedents are more vulnerable to the disintegration of the personahty than others (Mandell & Geyer, 1980). The acute consumption of such substances provokes mood changes, usually euphoric, alterations of the meaning of the time and visual or auditory perception, and in high doses, depersonalization and derealization (Isbell, Gorodetsky, Jasinski, Claussen, Spulak, & Korte, 1967). Clark (1968) reported acute consumption produces deterioration of complex reaction time and memory for digits. Weil, Zinberg, and Nelsen (1968) stated that consumption intoxicated mildly, and in a later analysis they indicated that individuals high on marijuana have subtle difficulties in speech; use of this substance interferes with retrieval of information from memory (Weil & Zinberg, 1969). A temporal disintegration and deterioration of immediate memory was observed by Melges, Tinklenberg, Hollister, and Gillespie (1970). Acute consumption decreased motor performance significantly (Manno, Kiplinger, Haine, Bennett, & Forney, 1970). According to Abel (1971), cannabis even produced interference in learning processes because its derivatives affect acquisition processes that contribute to the storage of information although these substances do not apparently affect the recovery of information from memory. When free recall is used, however, the recognition processes are affected. Dornbush, Fink, and Freedman (1971) support the results obtained on memory: marijuana affects short-term memory and reaction time. Chronic consumption of cannabis derivatives has also been stuhed. One 'Preparation of this paper was supported by the Consejerla de Educacibn y Ciencia (Junta de Andalucla) Consolidaci6n de Grupos de Investigaci6n y Desarrollo Tecnol6gico (BOJA 15/8/90). Requests for reprints should be sent to JosC Le6n-Carribn, Departamento de Psicologia Evolutiva y de la Educacibn, Bhsica y Metodologia, Universidad de Sev~Ua,Avda. San Francisco Javier s/n, 41005 Sevilla, Spain.
of the first reports by Soueif (1967) in Egypt indicated that the users of this drug showed alterations in memory and thought throughout a conversation. These results coincided with observations made later by Mendhiratta, Wigg, and Verma (1978) that the users of these drugs suffered from motor-perceptive disorders, deterioration of memory, and difficulties in concentration. The possibility that chronic consumption of cannabis produces cerebral damage has also been noted by several authors (Campbell, Evans, Thomson, & Williams, 1971; Kolansky & Moore, 1972); although Tulving, Thuling, Risberg, and Warkentin (1986), in studying regional cerebral blood flow in long-term heavy cannabis users, found no significant abnormalities in flow. The global CBF reduction seen in the early phase of detoxification is most likely the consequence of the dysfunction in the central nervous system accompanying chronic cannabis use. Moreover, Lebn-Carribn and Vela-Bueno (1990) found that chronic consumption of these substances can affect cognitive styles and the brain, altering the Basic Rest Activity Cycle between the cerebral hemispheres. The study described here concerns how chronic consumption of cannabis derivatives affects mental execution and intellectual skdls, focussing on heavy users who have never been diagnosed or treated for psychiatric problems and appear to function normally in their social community.
Subjects
To carry out this study we tested a group of cannabis users and a control group. The criteria for belonging to the cannabis group were that each was a regular smoker or user of cannabis derivatives (hashish), male, in the age range between 18 and 27 yr., with more than six mo. of daily consumption, right lateral dominance, no consumption of other drugs, no personal or family psychopathological antecedents, education below the last year of high school in Spain, preferably employed or unemployed workers, who had the same socioeconomic and cultural status, i.e., they all were friends and lived on the same street in the same neighbourhood, and had no left-handed family members. The control group had basically the same characteristics except for the fact that they had never smoked or used cannabis. The mean consumption rate of smokers was 2.5 cigarettes daily, and the mean length of consumption was 4.5 yr. From a sample of 181 individuals 45 subjects were selected and agreed to take part, 23 for the cannabis group and 24 for the control group. For various reasons such as previous psychopathology, use of other drugs, etc. 134 were excluded. Procedure
The Wechsler Adult Intelligence Scale (WAIS) was administered accord-
CANNABIS USE AND MENTAL PERFORMANCE
949
ing to the instructions for administration, assessment, and interpretation proposed by Wechsler (1958). All subjects were administered a questionnaire about drug use, a questionnaire on psychopathology, a clinical interview, and the Lateral Dominance Examination of the Halstead-Reitan Neuropsychological Test Battery. The means and standard deviations for each variable for each group were calculated, and the significance of differences between group means were estimated by Student's t.
The means and standard deviations for all WAIS measures by the control group and the smokers' group are given in Table 1. Analysis indicated significant differences between the two groups on nine of the 14 variables. TABLE 1 MEANSAND STANDARD DEVIATIONS FOR23 CANNABIS SMOKERSA N D 24 CONTROL SL~ECTS
WAIS Subscales
Cannabis M SD
Control M
t
P
SD
Information Comprehension
Arithmedc Similarities Digit Span
Vocabulary Digit Symbol Picture Completion Block Design Picture Arrangement Object Assembly Verbal IQ Performance IQ F d Scale IQ
Cannabis users showed that total IQ was lower than that of nonusers (t = 9.75, p < ,001) and that Verbal IQ and the Performance IQ were much lower (t = 8.21, p > ,001 and t = 7.68, p < .001, respectively). The largest significant difference between the groups on the different subtests of the test can be seen on Comprehension, on which the smokers obtained a lower score than the control group (t= 9.13, p < .001). We also observed that the group of hashish users obtained a lower score than was expected for their age, which could be understood as a pathological sign because, according to the general manual for the whole test, they should have obtained higher scores. Vocabulary and Object Assembly are the other subtests on which significantly lower scores were noted for smokers (t = 4.01, p < .001 and t = 3.98, p < .OO1, respectively).
O n six of the 14 WAIS measurements cannabis users showed lower mean scores than the control group (p
