text, we'll be using a number of specialized terms and expressions
that you may know better by other, "everyday" meanings.
To minimize confusion, we'll define terms this way:
non-nutritional chemical that alters body functions, producing
physical, psychological, or behavioral change.
Psychoactive Drug: A natural or synthetic substance
that affects mental processes or alters mood or behavior.
Drug Use: The intake of a chemical substance, whether or
not the substance is used medically or legally.
Drug Abuse: The intake of a chemical substance under circumstances
or at dosage levels that significantly increase risks of harm,
whether or not the substance is licit or illicit.
Psychological Dependence: A tendency for repeated or compulsive
use of a chemical, or involvement in an activity, because its
effects are considered pleasurable or satisfying, or because
it reduces undesirable feelings. A person may be psychologically
dependent on drugs, food, television, sex, relationships, or
A further distinction
can be drawn between gratification dependence, in which
major withdrawal symptoms are generally minor or absent, and
emotional dependence, in which serious withdrawal symptoms
appear after use stops.
Physical Dependence: Adaptation of body tissues to the continued
presence of a chemical, revealed in the form of serious, even
life-threatening withdrawal symptoms. The extent of physical
dependence and the severity of withdrawal symptoms can vary,
from drug to drug, and by amount, frequency, and duration of
Tolerance: Development of body resistance to the effects
of a chemical so that larger doses are required to reproduce
the original effect. When tolerance develops rapidly (as with
LSD), the user may be forced to stop use until tissues regain
When tolerance develops slowly and the chemical also produces
physical dependence (e.g. heroin, alcohol), the increased dose
requirements speed up and intensify the development of physical
Addiction: A state of chemical abuse characterized by a
high level of physical and/or psychological dependence.
When an addicting substance is abruptly stopped, withdrawal symptoms
appear and additional doses are necessary to ease those symptoms
or to produce the original effects.
A hallmark of addiction is continued, compulsive use despite
serious consequences -- such as health problems and the loss
of job or family.
An endless number
of schemes could be (and have been, in fact) designed to classify
the many drugs of abuse. Each grouping has its own strengths
and weaknesses, but none ever sorts all substances into "perfect"
We've chosen a relatively straightforward model that lumps substances
into three simple categories: "over-the-counter drugs,"
"prescription drugs," and "street drugs."
This is not to imply that drugs exist in only one category or
another. There's a great deal of movement across even the lines
we've selected. For example, the nonprescription stimulants caffeine
and phenylpropanolamine are listed alongside their chemical cousin
methamphetamine in the "street drugs" category, to
avoid endless redundancy and because of space limitations in
the booklet format.
In the same way, narcotic analgesics are listed as "prescription
drugs," although they're commonly bought and sold on the
street, since treatment of pain is their primary purpose.
Still, and in spite of the confusion factor, we hope that what
follows is a workable guide to the relative risks of common drugs