ingestion of substances, physiological changes due to
acute or chronic use of substances, and physiological
adaptations to the level of exposure to the substances.
Physiological reactivity occurs in response to the sub-
stance and results in metabolic changes in the body. Sub-
stances activate the pleasure-reward system in the brain,
which often results in euphoria. Acute or chronic sub-
stance abuse can cause neurotoxicity and damage to vital
organs. Commonly experienced cognitive impairments
include difficulties with short-term and working mem-
ory; problems with executive cognitive functions related
to decision making, problem solving, impulse control,
and abstraction; and, in some cases, difficulties with bal-
ance and motor functions. Existing evidence suggests
that some physiological changes are reversible, including
cognitive impairment, after a period of abstinence.
Psychological processes include behavioral, cogni-
tive, and emotional responses to substance use.
Behavioral processes operate according to learning prin-
ciples. Classical conditioning in substance abuse occurs
when particular stimuli are paired or associated with
substance use. In substance abuse research, these stim-
uli are often referred to as cuesor triggers.Substance use
may occur at an automatic level when cues trigger sub-
stance use so quickly that the individual may be momen-
tarily unaware of actions. Common triggers or cues
include places, situations, things, physical senses (sen-
sations, sights, sounds, smells, and tastes), emotions, or
events that become paired with substance use and may
trigger cravings or desires to use.
Operant conditioning operates when substance use
is reinforced or punished. Positive reinforcement is
conceptualized as a consequence following a behavior
that is rewarding or pleasurable and makes it likely that
the behavior will be repeated. Substance use can have
rewarding properties that positively reinforce the
behaviors related to substance use. In addition, sub-
stance use can be negatively reinforced. Negative rein-
forcement occurs when an aversive consequence is
lifted or withdrawn, which in effect reduces an aversive
experience. Because the aversive consequence is with-
drawn or reduced, it makes it more likely that the
behavior will be repeated. An example of this process is
when someone uses substances because it has reduced
pain or discomfort previously (negatively reinforced) as
opposed to using substances because it has caused
euphoria in the past (positive reinforcement). An excel-
lent and common example of substance use being neg-
atively reinforced among users is when they described
using substances to “self-medicate” symptoms. The
behavior described as self-medication alludes to ahistory where the substance use may have caused aver-
sive symptoms to subside. Research has demonstrated
that punishment can effectively stop or reduce sub-
stance use over the short term but that for long-term
changes to occur punishment must be followed by
learning new behavior and having that reinforced.
Substance abuse is difficult to change because it is
reinforced on a variable schedule. Since substances
are sometimes reinforcing and sometimes not, the
user cannot predict when substance use will be rein-
forcing and continues using substances in the hope
that the next event will be reinforcing. Variable rein-
forcement is one process that contributes to the transi-
tion from recreational use to substance abuse.
Observational learning also is a powerful predictor
of substance use. Youths and young adults are very
much influenced by observing and then modeling the
behaviors of significant others in their lives. Before
adolescence, youths tend to model the substance use
behavior of their parents. Researchers have noted that
substance abuse tends to be intergenerational in family
systems. The assumption for many years was that this
intergeneration “transmission” of substance abuse must
be genetic. However, recent research has identified that
at least part of the intergenerational phenomenon in
family systems appears to be learned behavior, princi-
pally from observing and modeling parents who misuse
substances. As youths move into the teen years and
early adulthood, peer groups tend to influence sub-
stance use more than parents. In addition, researchers
have found that adolescents and young adults tend to
overestimate the substance use of peers and at the same
time underestimate their own substance use.
Cognitive factors related to addictive processes
include expectancies about substance use, motivation to
change, and self-efficacy. Expectancies are beliefs about
the expected effects of substance use. Expectancies can
develop through personal experience or observational
learning. As an example of the latter, to sell their prod-
ucts advertisers of alcohol beverages often advertise that
alcohol makes people sexy or socially attractive, beliefs
that are assumed by youths who observe the advertise-
ments. Positive expectancies refer to beliefs that sub-
stance use will provide a desirable outcome, whereas
negative expectancies refer to beliefs that substance use
will lead to an undesirable outcome. Positive expectan-
cies have been found to predict continued and some-
times increased substance use, whereas negative
expectancies have been linked to reductions.
Motivation to change determines whether a user
will consider and ultimately change substance use.Substance Use Disorders——— 779S-Cutler (Encyc)-45463.qxd 11/18/2007 12:44 PM Page 779