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Marijuana is
not a completely benign substance. It is a powerful
drug with a variety of effects. However, except for
the harms associated with smoking, the adverse effects
of marijuana use are within the range of effects tolerated
for other medications. The harmful effects to individuals
from the perspective of possible medical use of marijuana
are not necessarily the same as the harmfull physical
effects of drug abuse. When interpreting studies purporting
to show the harmful effects of marijuana, it is important
to keep in mind that the majority of those studies
are based on smoked marijuana, and cannabinoid effects
cannot be separated from the effects of inhaling smoke
from burning plant material and contaminants. |
For most people, the primary adverse effect of acute marijuana
use is diminished psychomotor performance. It is, therefore,
inadvisable to operate any vehicle or potentially dangerous
equipment while under the influence of marijuana, THC, or
any cannabinoid drug with comparable effects. In addition,
a minority of marijuana users experience dysphoria, or unpleasant
feelings. Finally, the short-term immunosuppressive effects
are not well established but, if they exist, are not likely
great enough to preclude a legitimate medical use.
The chronic effects of marijuana are of greater concern for medical
use and fall into two categories: the effects of chronic smoking,
and the effects of THC. Marijuana smoking is associated with abnormalities
of cells lining the human respiratory tract. Marijuana smoke, like
tobacco smoke, is associated with increased risk of cancer, lung
damage, and poor pregnancy outcomes. Although cellular, genetic,
and human studies all suggest that marijuana smoke is an important
risk factor for the development of respiratory cancer, proof that
habitual marijuana smoking does or does not cause cancer awaits
the results of well-designed studies.
A second concern associated with chronic marijuana use is
dependence on the psychoactive effects of THC. Although few
marijuana users develop dependence, some do. Risk factors
for marijuana dependence are similar to those for other forms
of substance abuse. In particular, antisocial personality
and conduct disorders are closely associated with substance
abuse. A distinctive marijuana withdrawal syndrome has been
identified, but it is mild and short-lived. The syndrome includes
restlessness, irritability,mild agitation, insomnia, sleep
EEG disturbance, nausea, and cramping.
Patterns in progression of drug use from adolescence to adulthood
are strikingly regular. Because it is the most widely used
illicit drug, marijuana is predictably the first illicit drug
most people encounter. Not surprisingly, most users of other
illicit drugs have used marijuana first. In fact, most drug
users begin with alcohol and nicotine before marijuana - usually
before they are of legal age. In the sense that marijuana
use typically precedes rather than follows initiation of other
illicit drug use, it is indeed a “gateway” drug.
But because underage smoking and alcohol use typically precede
marijuana use, marijuana is not the most common, and is rarely
the first, “gateway” to illicit drug use.
There is no conclusive evidence that the drug effects of marijuana
are causally linked to the subsequent abuse of other illicit drugs.
An important caution is that data on drug use progression cannot
be assumed to apply to the use of drugs for medical purposes. It
does not follow from those data that if marijuana were available
by prescription for medical use, the pattern of drug use would remain
the same as seen in illicit use.
Division of Neuroscience, Institute of Medicine, Washington,
2002.
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