Marijuana: A Continuing Concern
for Pediatricians
Committee on Substance
Abuse
ABSTRACT
Marijuana,
the common name for products derived from the plant Cannabis sativa, is the
most common illicit drug used by children and adolescents in the United States.1
Despite growing concerns by the medical profession about the physical and
psychological effects of its active ingredient, 
-9-tetrahydrocannabinol,
survey data continue to show that increasing numbers of young people are using
the drug as they become less concerned about its dangers.1
ABBREVIATION: THC, tetrahydrocannabinol.
Because
the decision of whether to use marijuana is usually made by the time a young
person reaches the age of 19 years,2,3
pediatricians must continue to be cognizant of the implications of marijuana
use. Widespread debate exists about marijuana and the possibility of legalizing
its use or at least decriminalizing its possession.4-7 Furthermore,
marijuana is being promoted for medical purposes, such as the treatment of glaucoma
and the management of nausea and anorexia related to cancer chemotherapy.4,8,9 Although these topics are beyond the scope of
this statement, evidence suggests that pediatricians should continue their
vigilant efforts to prevent the use of this drug by young people. The abuse of
marijuana by adolescents is a major health problem with social, academic,
developmental, and legal ramifications.10 Marijuana is an addictive,
mind-altering drug capable of inducing dependency.11 Pediatricians
are obligated to develop a reasoned approach to dealing with its use by
children and adolescents so they can provide appropriate care and counsel.12
EPIDEMIOLOGY
Between
1991 and 1997, the use of marijuana by young people increased dramatically.1
In 1997, 23% of eighth graders reported having used the drug at some time in
their lives, an increase in use from 10% in 1991. Among 10th
graders, the number nearly doubled from 23% in 1991 to 42% in 1997. In 1997,
50% of high school seniors reported having used marijuana compared with 37% 6
years earlier. The abuse of marijuana among teenagers has increased as the
"perceived harmfulness" of regular use has decreased and the
perception of "peer acceptance" has increased.1,2
POTENCY
The
potency of marijuana is defined as the percentage of -9-tetrahydrocannabinol
(-9-THC) in
the dry weight of the sample. Increased sophistication in the selective
breeding of marijuana plants has led to a substantial increase in the potency
of street samples during the past 2 decades. In 1975, the average potency of
THC in confiscated samples was 0.71%; by 1997, the average concentration was
3.71% -- a five-fold increase. There is wide variation in the potency of smoked
marijuana. Sensimilla (considered by many to be the finest product, produced
from the flowering tops of the female hemp plant) had an average potency of
6.6% in 1997. Marijuana sold as loose plant material (leaves, stems, and seeds)
had an average potency of 3.2%.13 In addition, the method of
consumption (smoking as a rolled cigarette or in a pipe or packed into a
hollowed-out cigar), as well as the presence of adulterating substances, affect
the potency. Because of the documented change in potency, pediatricians must be
able to address with their patients what seems to be "casual use" of
marijuana. Trends suggest that the low-dose, self-experimentation type of use
typical of the 1960s may be giving way to the high-potency -- high-reward
pattern of compulsive marijuana use prevalent during the late 1990s.14
SOMATIC
CONSEQUENCES
Marijuana
should not be considered an innocuous drug. Regular use has been associated
with cardiovascular, pulmonary, reproductive, and immunologic consequences. The
physiologic effects of marijuana use include an accelerated heart rate and a
minimal rise in blood pressure.15,16 These
effects, which seem to be secondary to -adrenergic
vascular mechanisms, are transient and usually not deleterious to the otherwise
healthy adolescent. The immediate pulmonary effect of smoking marijuana is
bronchodilation, although with long-term use the smoked particles act as an
irritant, causing bronchoconstriction and eventual airway obstruction.17-19
The chronic effects are similar to those of smoking
tobacco, and there seems to be a relationship between smoking marijuana and
neoplastic changes in the lungs.20
Heavy
marijuana use may be especially dangerous for adolescents during puberty. Such
use has been associated with diminished sperm motility, decreased sperm counts,
decreased circulating testosterone levels,21,22
irregular ovulation, and decreased pituitary gonadotropin levels.23,24
The metabolites of marijuana cross the human placenta and are also found in
human milk. Although the consequences of the presence of such metabolites in
human milk have yet to be identified,25-27
infants born to mothers who smoke marijuana during pregnancy are shorter, weigh
less, and have smaller head circumferences at birth.27,28 Marijuana
and some of its components influence the immune system and affect the body's
antitumor activities. Marijuana receptors have been identified on macrophages
and T and B lymphocytes, suggesting a molecular basis for immunosuppression by
THC.29-31
NEUROPHARMACOLOGY
The
psychoactive effects of -9-THC are receptor-mediated. The cannabinoid receptor sites in the
brain are particularly dense in the outflow nuclei of the basal ganglia, the
hippocampus, and the molecular layers of the cerebellum, implicating roles for
cannabinoids in the disruption of cognition and coordination. Sparse densities
in the lower brainstem areas controlling cardiovascular and respiratory
functions may explain why high doses of -9-THC are
not lethal.32
Anandamide,
a derivative of arachidonic acid, is an endogenous chemical in the brain that
binds with cannabinoid receptors.33 Like -9-THC, it
has been shown to affect muscle coordination, produce analgesic and
tranquilizing effects, and inhibit secretion of follicle-stimulating hormone,
prolactin, and growth hormone.34 The use of anandamide as a
marijuana antagonist has substantial effects on rats conditioned to
self-treatment with THC33,34 and has helped elucidate the mechanism
by which cannabinoids exert their biological and psychologic effects.
The
most pervasive common pathway among drugs of abuse, including cocaine, heroin,
opiates, and marijuana, is the stimulation of release of the neurotransmitter,
dopamine.35-38 This endogenous catecholamine stimulates certain
dopaminergic projections of the medial forebrain bundle--the brain's so-called
reward circuitry.39 Psychoactive drugs, including marijuana, derive
substantial abuse liability from enhancing these circuits; and it is the
psychoactive ingredient of marijuana, -9-THC,
that stimulates the release of dopamine, mediated through the cannabinoid
receptors.40,41
In
both animal and human experiments, subjects self-administer marijuana. They
predictably select high-potency marijuana over low-potency marijuana,42 supporting the hypothesis that the
reinforcing effect and abuse liability of marijuana are positively related to
the -9-THC
content.
Marijuana
is lipophilic and is stored in the brain and other fat-rich areas of the body,
forming what has been described as a "depot."43 The slow
release of marijuana and its metabolites from lipid stores may explain the
carry-over effects of marijuana on driving and other cognitive and behavioral
changes,44 as well as the absence of acute
signs of withdrawal after abrupt discontinuation of use.45
BEHAVIORAL
AND COGNITIVE CONSEQUENCES
Marijuana
affects the brain, resulting in behavioral and cognitive effects. Acutely,
marijuana produces euphoria, relaxation, and disinhibition. Persons under the
influence of the drug show impaired problem- solving skills and difficulty in
organizing thoughts and conversing. Other adverse consequences of marijuana use
include interference with coordination; the ability to judge elapsed time,
speed, and distance; the ability to track a moving object; and reaction time.46-49
There is little doubt that marijuana intoxication contributes substantially to
accidental deaths and injuries among adolescents, especially those associated
with motor vehicle crashes, and is frequently involved in incidents related to
driving while intoxicated.50,51 Regular use of marijuana also exerts
a negative effect on short-term memory, learning, and attention span. Three
methodologically strong studies presented compelling evidence that these
functions were impaired in frequent users of marijuana (defined as using 20 to
30 days per month), even up to 6 weeks after discontinuation of use,52 and noticeable impairment in attention and
memory was evident even after 24 hours of abstinence.53,54 Clearly,
young people who are frequent users of marijuana experience residual
neuropsychologic effects with an impaired ability to learn.53
An
"amotivational syndrome" has been described in chronic heavy
marijuana users. This syndrome is characterized by the inability to sustain
attention on environmental stimuli and to maintain goal-directed thinking and
behavior.55 An additional source of concern is the occasional
occurrence of dysphoric reactions that may range from mild fear to
depersonalization to frank paranoia.56,57
Finally,
marijuana use often precedes the use of other more dangerous drugs. Although
marijuana use does not necessarily predict progression to the use of
"harder" drugs, adolescents who use marijuana are 104 times as likely
to use cocaine compared with peers who never smoked marijuana.4,58 Therefore, the use of marijuana as a risk behavior
and its role as a "gateway drug" for some teenagers must be
considered.
SUMMARY
The
seriousness of the behavioral consequences of marijuana use is sufficient to
cause great concern and should prompt the pediatrician to counsel young people
against any use of the drug. Such counsel should be based on health concerns,
including the relationship of marijuana use to trauma associated with
intoxication and the effect on memory and learning during this important period
of development. Additional reasons for concern and counsel include anxieties
and uncertainties about the potential harm that marijuana use may cause to
adolescents during a period of rapid change in hormonal secretion, possible
teratogenicity, and the known consequences of long-term use. A discussion of
drug use, including the use of marijuana, should be a routine part of primary
health care clinical preventive services for every child and adolescent. An
assessment of potential drug use gives the pediatrician the opportunity to
offer anticipatory guidance before the onset of drug use, to intervene and
minimize consequences if drug use has begun, and to detect and address issues
of long-term or heavy use. Although all users should be counseled about the
dangers of the drug and the illicit nature of its use, marijuana is an
addictive drug and is capable of producing dependency. Marijuana-dependent
teenagers should be offered treatment options, rather than simply punishment,
for their illness.
COMMITTEE ON SUBSTANCE ABUSE, 1998-1999
Richard B. Heyman, MD, Chairperson
Trina M. Anglin, MD
Stuart M. Copperman, MD
Catherine A. McDonald, MD
Peter D. Rogers, MD, MPH
Rizwan Z. Shah, MD
LIAISON REPRESENTATIVES
Marie Armentano, MD
Gayle M. Boyd, PhD
National Institute of Alcohol Abuse and Alcoholism
Dorynne Czechowicz, MD
National Institute on Drug Abuse
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Pediatrics
Volume 104, Number
The
recommendations in this statement do not indicate an exclusive course of
treatment or serve as a standard of medical care. Variations, taking into
account individual circumstances, may be appropriate.
© Copyright 1999 by the
No part of this statement may be reproduced in any form or by any means
without prior written permission from the