Reprint Series SCIENCE
24 July 1981, Volume 213, pp. 465-466
Cognition and Long-Term Use of Ganja (Cannabis)
Jeffrey Schaeffer, Therese
Andrysiak, and J. Thomas Ungerleider
Copyright 1981 by the American Association for the
Advancement of Science
Cognition and Long-Term Use of Ganja (Cannabis)
Abstract. Neuropsychological variables and urine cannabinoid
metabolites were
evaluated in ten subjects born, raised, and educated in the
United States and having histories
of heavy or prolonged use of cannabis.
No impairment of cognitive function was found.
Cannabinoid metabolites in
excess of 50 nanograms per milliliter were present in the ten
urine
samples. The tetrahydrocannabinol content of cannabis exceeded 8.0 percent.
Several studies have attempted to characterize the mental or cognitive
functioning of persons
with histories of heavy and prolonged use of ganja
(cannabis). Generally, investigators have
concluded that heavy and
prolonged use has not led to impairment of mental and cognitive
functions
consistent with brain or cerebral dysfunction (1-4).
Although several studies
have shown decrements in neuropsychological
performance among those with brief or sporadic
patterns of cannabis use here
in the United States (5-9), comparable studies of prolonged
heavy use in
this country have not been performed. Thus, the only available literature
is based on studies conducted in foreign countries (Jamaica, Greece, Egypt,
and Costa
Rica).
We had the opportunity to observe a group of long-term heavy users of
ganja in
both a Southern state and a Caribbean island. The ganja was used
by this group for religious
purposes and symbolized the sacrament of
communion–"the Green Herb of the Bible."
It was used, as we observed, even
during the extensive neuropsychological evaluations that we
completed, in a
continuous and ritualistic manner throughout virtually all waking hours.
Very large cigarettes (or "spliffs") and pipes, containing ganja mixed with
tobacco,
were regularly shared by members of the group (10).
We examined ten subjects (seven males and
three females) ranging in age
from 25 to 36 years. The mean number of years of education was
13.5 (all
were born, raised, and educated in the United States), and all were
Caucasian.
None had any history of disease that could be related to central
nervous system dysfunction.
By their own report, they used between 2 and 4
ounces of the ganja-tobacco mixture per day,
with a reported mean duration
of use of 7.4 years (the time since joining this particular
church). All
subjects actively engaged in daily work, largely agricultural and business,
and led active and spiritually oriented lives (10). It was not possible to
collect control
data in this environment, as all church members continuously
smoked ganja. Thus, comparisons
were made with the published standards and
normative data for the psychometric instruments
used.
Subjects in this study agreed to provide approximately 15 ml of fresh
urine for
enzyme immunoassay of cannabinoid metabolite content. Specimens
were preserved with
approximately 4 mg of sodium azide per 15 ml of urine
that was collected. Urine samples for
each of the ten individuals studied
were obtained immediately before each subject began a
series of selected
neuropsychological tests designed to assess a broad range of cognitive
A modified version of the Michigan Neuropsychological Test Sequence was
used (11-13). Each subject was administered exactly the same group of tests
in exactly the
same order. General intellectual functioning was assessed on
the basis of a prorated version
of the Wechsler Adult Intelligence Scale
(Table 1) (14). Additional neuropsychological tests
included the
following: Benton Visual Retention Test (administration C) (15), Rey
Auditory-Verbal Learning Test (16), Symbol-Digit Modalities Test (17),
Hooper Visual
Organization Test (18), Raven’s Progressive Matrices Test
(19), and Trailmaking Test (forms A
and B) (20). The following cognitive
functions were assessed: language areas of function,
nonlanguage areas of
function, memory, complex multimodal learning, and general
intellectual
functioning. Auditory and visual memory functions included remote (years
and months), recent (weeks, days, hours, minutes), and immediate events
(within seconds).
urine samples. The
assay is a semiquantitative immunochemical test designed
to detect a level of at least 50 ng
of 11-nor-delta-9-tetrahydrocannabinol
cabboxylic acid per milliliter of urine with greater
than 95 percent
confidence. Each of the ten urine samples contained concentrations of
cannabinoids at 50 ng/ml (one subject) or well above this level (nine
subjects).
None of
the neuropsychological test data indicated impairment of
cognitive functioning. Language areas
of function, nonlanguage areas of
function, memory, complex multimodal learning, and general
level of
intellectual functioning were all completely unimpaired, compared with
standardized-normative information available for each test (Table 1).
The mean IQ scores
(Table 1) are all in the superior to very superior
range of intellectual functioning, ranging
from the upper 6.7 percent to the
upper 2.2 percent of the population (14). Scores obtained on
all of the
other psychometric tests were also well within the normal range for age
(11-20). There was nothing found in any of the ten subjects’ protocols that
might suggest
impaired mental functioning due to brain or cerebral
dysfunction resulting from heavy and
prolonged use of ganja.
While several previous studies have reported transient cognitive
impairment resulting from the acute effects of cannabis, primarily with
respect to
attention-concentration and visuomotor (hand-eye) coordination
(8, 9, 22, 23), none of the
studies involving prolonged and heavy use of
ganja have shown any systematic decrements in
mental abilities suggestive of
impairment of brain or cerebral function and cognition (14).
metabolites, observed the
inhalation of cannabis by all subjects studied,
and analyzed samples of this cannabis for THC.
Analysis of cannabis mixed
with tobacco (by gas chromatography) yielded a delta-9-THC content
of 4.14
percent (half cannabis, half tobacco); thus the THC content of the pure
cannabis
exceeds 8.0 percent.
We observed no transient decrements in cognitive functioning that
often
accompany intermittent or sporadic use of cannabis. The development of
tolerance
to one or more of the constituents of cannabis may explain this
phenomenon.
Although the
obtained IQ scores were high, one could speculate that
perhaps cannabis had produced a priori
declines in IQ scores for all ten
subjects, as well as scores on other neuropsychological
measures. It was
possible for us to obtain early school academic achievement test data on
two
of our subjects. These data included equivalent IQ conversion scores
virtually
identical to those we measured for those subjects. We realize
that these conversion or
equivalent IQ scores derived from early school
achievement test data are not to be equated on
a one-for-one basis with
current scores. However, we do believe that IQ score ranges provide
a
reasonable degree of equivalency. These achievement test scores were
obtained some 15
to 20 years earlier, long before either subject began the
use of cannabis, by their report to
us.
Finally, we stress the commitment of the ten subjects to their religious
sect and
way of life. They told us and others (10) that members of the
church do not use substances
(drugs, alcohol, or psychoactive herbs other
than ganja, and we observed them to maintain a
regular diet consisting
primarily of vegetables, fruit, and small amounts of meat. All ten
subjects
(as well as other members of the church) appear to be healthy and highly
functional individuals adhering to a strict religious doctrine.
JEFFREY SCHAEFFER
Department of Psychiatry and
Biobehavioral Sciences. University of
California School of
Medicine,
Los Angeles 90024, and
Neuroscience Associates Incorporated,
Los Angeles
90048
THERESE ANDRYSIAK
J. THOMAS UNGERLEIDER
Department of Psychiatry
and
Biobehavioral Sciences, University of
California School of Medicine
Table 1. Summary of neuropsychological data (means ± standard
deviations).
Test Number
Scaled
correct score
Wechsler Adult Intelligence Scale
Information 26.2 ± 3.12
16.5 ± 2.55
Arithmetic 15.2 ± 2.10 14.3 ± 1.95
Similarities 20.8 ± 2.30 14.2 ±
1.97
Digit symbol 69.6 ± 8.73 13.8 ± 2.49
Block design 42.7 ± 5.96 13.8 ± 2.39
Picture arrangement 29.1 ± 5.30 13.0 ± 2.98
Verbal IQ* 129.0 ± 10.87
Performance IQ*
124.2 ± 13.07
Full-scale IQ* 128.4 ± 10.36
Other instruments
Benton 8.8 ±
1.02
Rey 14.9 ± 0.32
Symbol-digit 60.4 ± 10.25
Hooper 28.7 ± 1.06
Raven
35.2 ± 0.79
Trailmaking (in
seconds) 28.8 ± 6.88¡
Form A 53.5 ± 15.28¡
Form B
*Prorated. ¡No errors.
References
1. V. Rubin and L.
Comitas, Ganja in Jamaica (Mouton, The Hague,
1975).
2. M. C. Braude and S. Szara, Eds.,
Pharmacology of Marijuana
(Raven, New York, 1976).
3. R. L. Dornbush and A. Kokkevi, in
(2), p. 421.
4. C. Stefanis, J. Boulougouris, A. Liakos, in (2), pp. 659-665.
5. I. M.
Frank, P. J. Lessin, E. D. Tyrrell, P. M. Hahn, Szara, in
(2), pp. 673-679.
6. S. Y.
Hill and D. W. Goodwin in (7), p. 139.
7. S. Cohen and R Stillman, Eds., The Therapeutic
Potential of
Marijuana (P1enium, New York, 1976).
8. L. L. Miller, in (7), pp.
271-292.
9. R. T. Jones and N. Benowitz, in (2), p. 627.
10. M. C. Dreher, personal
communication (March 1980).
11. A. Smith, in Drugs, Development and Cerebral Function. W.
L.
Smith, Ed. (Thomas. Springfield, Ill., 1972), pp. 27-68.
12. _____ and C. W.
Burkland, paper presented at the annual meeting
of the American Psychological Association,
1967.
13. _____, Science 153, 1280 (1966).
14. D. Wechsler, Manual for the Wechsler
Adult Intelligence Scale
(Psychological Corporation, New York, 1955).
15. A. Benton,
Revised Visual Retention Test: Clinical and
Experimental Applications (Psychological
Corporation, New York,
ed. 4, 1974).
16. M. Lezak. Neuropsychological Assessment (Oxford
Univ. Press, New
York, 1976).
17. A. Smith, Symbol Digit Modalities Test Manual
(Western
Psychological Services, Los Angeles, 1973).
18. E. Hooper, The Hooper Visual
Organization Test (Western
Psychological Services, Los Angeles, 1973).
19. J. C. Raven,
Guide to Using the Coloured Progressive Matrices
(Lewis, London, 1965).
20. R. M.
Reitan, Percept. Motor Skills 8, 271 (1958).
21. Cannabinoid Urine Assay: Emit Cannabinoid
Assay (Syva, Palo
Alto, 1980).
22. R. A. Harshman, H. Crawford, E. Hecht, in (7), pp.
205-254.
23. "Human effects," in Marihuana Research Findings (National
Institute of Drug Abuse Monorgaph No. 14, Government Printing
Office, Washington, D.C., 1977),
p. 128.
23 September 1980; revised 9 January 1981
Individual results for
Carl Olsen
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