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Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
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OCR for page 36
36
APPENDIX: SUMMARY OF MARIJUANA AND HEALTH
The Institute of Medicine (ION) of the National Academy
of Sciencen has conducted a 15-month study of the
health-related effects of marijuana, at the request of
the Secretary of Health and Human Services and the
Director of the National Institutes of Health. The IOM
appointed a 22-member committee to:
· analyze existing scientific evidence bearing on
the possible hazards to the health and safety of
. . .
users o : marijuana;
· analyze data concerning the possible
therapeutic value and health benefits of marijuana;
. ~. . . .
assess federal research programs In marijuana;
zoentzzy promising new research directions, and
make sugggestions to improve the quality and
usefulness of future research; and
draw conclusions from this review that would
accurately assess the limits of present knowledge and
thereby provide a factual, scientific basis for the
development of future government policy.
This assessment of knowledge of the health-related
effects of marijuana is important and timely because
marijuana is now the most widely used of all the illicit
drugs available in the United States. In 1979, more
than 50 million persons had tried it at least once.
mere has been a steep rise in its use during the past
decade, particularly among adolescents and young adults.
although there has been a leveling-off in its overall
use among high school seniors in the pas t 2 or 3 years
and a Small decline in the Percentage of seniors who use
.
it frequently. Although substantially more high school
students have used alcohol than have ever used
marijuana, more high school seniors use marijuana on a
daily or near-daily basis (9 percent) than alcohol (6
percent). Much of the heavy use of marijuana, unlike
alcohol, takes place in school, where effects on
behavior, cognition, and psychomotor performance can be
particularly disturbing. Unlike alcohol, which is
rapidly metabolized and eliminated from the body, the
psychoactive components of marijuana persist in the body
for a long time. Similar to alcohol, continued use of
marijuana may cause tolerance and dependence. For all
these reasons, it is imperative that we have reliable
ant detailed information about the effects of marijuana
use on health, both in the long and short term.
OCR for page 37
37
What, then, did we learn from our review of the
published scientific literature? Numerous acute effects
have been described in animals, in isolated cells and
tissues, and in studies of human volunteers; clinical
and epidemiological observations also have been
reported. This information is briefly summarized in the
following paragraphs.
EFFECTS ON THE NERVOUS SYSTEM AND ON BEHAVIOR
We can say with confidence that marijuana produces acute
effects on the brain, including chemical and
electrophysiological changes. its most clearly
established acute effects are on mental functions and
behavior. With a severity directly relates to dose,
marijuana impairs motor coordination and affects
tracking ability and sensory and perceptual functions
important for safe driving and the operation of other
machines; it also impairs short-term memory and Blown
learning. Other acute effects include feelings of
euphoria and other mood changes, but there also are
disturbing mental phenomena, such as brief periods of
anxiety, confusion, or psychosis.
There is not yet any conclusive evidence as to
whether prolonged use of marijuana causes permanent
changes in the nervous system or sustained impairment of
brain function and behavior in human beings. In a few
unconfirmed studies in experimental animals, impairment
of learning and changes in electrical brain-wave
recordings have been observed several months after the
cessation of chronic administration of marijuana. In
the judgment of the committee, widely cited studies
purporting to demonstrate that marijuana affects the
gross and microscopic structure of the Herman or monkey
brain are not convincing; Mach more work is needed to
settle this important point.
Chronic relatively heavy use of marijuana is
associated with behavioral dysfunction and mental
disorders in human beings, but available evidence does
not establish if marijuana use under these circumstances
is a cause or a result of the mental condition. There
are similar problems in interpreting the evidence
linking the use of marijuana to subsequent use of other
illicit drugs, such as heroin or cocaine. Association
does not prove a causal relation, and the use of
marijuana may merely be symptomatic of an underlying
.
OCR for page 38
38
disposition to use psychoactive drugs rather than a
"stepping stone" to involvement with more dangerous
substances. It is also difficult to sort out the
relationship between use of marijuana and the complex
symptoms known as the amotivational syndrome.
Self-selection and effects of the drug are probably both
contributing to the motivational problems seen in some
chronic users of marijuana.
Thus, the long-tenm effects of marijuana on the human
brain and on human behavior remain to be defined.
Although we have no convincing evidence thus far of any
effects persisting in human beings after cessation of
drug use, there may well be subtle but important
physical and psychological consequences that have not
been recognized.
EFFECTS ON THE CARDIOVASCULAR AND RESPIRATORY SYSTEMS
There is good evidence that the smoking of marijuana
usually causes acute changes in the heart and
circulation that are characteristic of stress, but there
is no evidence to indicate that a permanently
deleterious effect on the normal cardiovascular system
occurs. There is good evidence to show that marijuana
increases the work of the heart, usually by raising
heart rate and, in some persons, by raising blood
pressure. This rise in workload poses a threat to
patients with hypertension, cerebrovascular disease, and
coronary atherosclerosis.
Acute exposure to marijuana smoke generally elicits
broncho-dilation; chronic heavy smoking of marijuana
causes inflammation and pre-neoplastic changes in the
airways, similar to those produced by Smoking of
tobacco. Marijuana smoke is a complex mixture that not
only has many chemical components (including carbon
monoxide and "tar") and biological effects similar to
those of tobacco smoke. but also some unioue
ingredients.
, .
This sugges es the strong possibility that
prolonged heavy smoking of marijuana, like tobacco, will
lead to cancer of the respiratory tract and to serious
impairment of lung function. Although there is evidence
of impaired lung function in chronic smokers, no direct
confirmation of the likelihood of cancer has yet been
provided, possibly because marijuana has been widely
smoked in this country for only about 20 years, and data
have not been collected systematically in other coun-
tries with a much longer history of heavy marijuana use.
OCR for page 39
39
EFFECTS ON THE REPRODUCTIVE SYSTEM AND ON CHROMOSOMES
Although studies in animals beve shown that delta-9-THC
(the major psychoactive constituent of marijuana) lowers
the concentration in blood serum of pituitary hormones
(gonadotropins) that control reproductive functions , it
is not known if there is a direct effect on reproductive
tissues. Delta-9-THC appears to have a modest
reversible suppressive effect on sperm production in
men, but there is no proof that it has a deleterious
effect on male fertility. Effects on human female
hormonal function have been reported, but the evidence
is not convincing. However, there is convincing
evidence that marijuana interferes with ovulation in
female monkeys. No satisfactory studies of the relation
between use of marijuana and female fertility and
child-bearing have been carried out. Although
delta-9-THC is known to cross the placenta readily and
to cause birth defects when administered in large doses
to experimental animals, no adequate clinical studies
have been carried out to determine if marijuana use can
harm the human fetus. There is no conclusive evidence
of teratogenicity in human offspring, but a slowly
developing or low-level effect might be undetected by
the studies done so far. The effects of marijuana on
reproductive function and on the fetus are unclear; they
may prove to be negligible, but further research to
establish or rule out such effects would be of great
importance.
Extracts from marijuana smoke particulates ("tar")
have been found to produce dose-related mutations in
bacteria; however, delta-9-THC, by itself, is not
mutagenic. Marijuana and delta-9-THC do not appear to
break chromosomes, but marijuana may affect chromosome
segregation during cell division, resulting in an
abnormal number of chromosomes in daughter cells.
Although these results are of concern, their clinical
significance is unknown.
THE IMMUNE SYSTEM
Similar limitations exist in our understanding of the
effects of marijuana on other body systems. For
example, some studies of the immune system demonstrate a
mild, immunosuppressant effect on human beings, but
other studies show no effect.
OCR for page 40
40
THERAPEUTIC POTENTIAL
The committee also has examined the evidence on the
therapeutic effects of marijuana in a variety of medical
disorders. Preliminary studies suggest that marijuana
and its derivatives or analogues might be useful in the
treatment of the raised intraocular pressure of
glaucoma, in the control of the severe nausea and
vomiting caused by cancer chemotherapy, and in the
treatment of asthma. mere also is some preliminary
evidence that a marijuana constituent (cannabidiol)
might be helpful in the treatment of certain types of
epileptic seizures, as well as for spastic disorders and
other nervous system diseases. But, in these and all
other conditions, much more work is needed. Because
marijuana and delta-9-THC often produce troublesome
psychotropic or cardiovascular side-effects that limit
their therapeutic usefulness, particularly in older
patients, the greatest therapeutic potential probably
lies in the use of synthetic analogues of marijuana
derivatives with higher ratios of therapeutic to
undesirable effects.
The NEED FOR MORE RESEARCH ON MARIJUANA
The explanation for all of these unanswered questions is
insufficient research. We need to know much more about
the metabolism of the various marijuana chemical
compounds and their biologic effects. This will require
many more studies in animals, with particular emphasis
on subhuman primates. Basic pharmacologic information
obtained in animal experiments will ultimately have to
be tested in clinical studies on human beings.
Until 10 or 15 years ago, there was virtually no
systematic, rigorously controlled research on the human
health-related effects of marijuana and its major
constituents. Even now, when standardized marijuana and
pure synthetic cannabinoids are available for
experimental studies, and good qualitative methods exist
for the measurement of delta-9-THO and its metabolites
in body fluids, well-designed studies on human beings
are relatively few. mere are difficulties in studying
the clinical effects of marijuana in human beings,
particularly the effects of long-term use. And yet,
without such studies the debate about the safety or
hazard of marijuana will remain unresolved. Prospective
as,
OCR for page 41
41
cohort studies, as well as retrospective case-control
studies, would be useful in identifying long-term
behavioral and biological consequences of marijuana use.
The federal investment in research on the
health-related effects of marijuana has been small, both
in relation to the expenditure on other illicit drugs
and in absolute teems. The committee considers the
research particularly inadequate when viewed in light of
the extent of marijuana use in this country, especially
by young people. We believe there should be a greater
investment in research on marijuana, and that
investigator-initiated research grants should be the
primary vehicle of support.
The committee considers all of the areas of research
on marijuana that are supported by the National
Institute on Drug Abuse to be important, but we did not
judge the appropriateness of the allocation of resources
among those areas, other than to conclude that there
should be increased emphasis on studies in human beings
and other primates. Recommendations for future research
are presented at the end of Chapters 1-7 of this report.
CONCLUSIONS
The scientific evidence published to date indicates that
marijuana has a broad range of psychological and
biological effects, some of which, at least under
certain conditions, are harmful to human health.
Unfortunately, the available information does not tell
us how serious this risk may be.
The major conclusion is that what little we know for
certain about the effects of marijuana on human
health--and all that we have reason to
suspect--justifies serious national concern. Of no less
concern is the extent of our ignorance about many of the
most basic and important questions about the drug. Our
major recommendation is that there be a greatly
intensified and more comprehensive program of research
into the effects of marijuana on the health of the
American people.
Representative terms from entire chapter:
marijuana smoke
