The Varying Effects of Drugs

156
FIGURE
Chapter 4 Consciousness
4.8
Agonists and Antagonists
In Part A, a molecule of neurotransmitter
interacts with a receptor on a neuron’s
dendrites by fitting into and stimulating it.
Part B shows a drug molecule acting as an
agonist, affecting the receptor in the same
way a neurotransmitter would. Part C depicts an antagonist drug molecule blocking a natural neurotransmitter from
reaching and acting on the receptor.
Neurotransmitter
blocked by
antagonist
Neurotransmitter
Drug acting
as agonist
Drug acting
as antagonist
Naturally occurring
neurotransmitter
Agonist
Antagonist
(A)
(B)
(C)
drug that blocks receptors for a certain neurotransmitter often leads to an increase in
the number of receptors available to accept that neurotransmitter.
The Varying Effects of Drugs
Unfortunately, chemical properties that give drugs their medically desirable main
effects, such as pain relief, often create undesirable side effects as well.
One side effect may be the potential for abuse. Substance abuse
is a pattern of use that causes serious social, legal, or interpersonal problems for the user
(American Psychiatric Association, 2000). Of course, as a culture changes, the drugs that
cause a person social and legal problems may also change, as Figure 4.9 illustrates.
Substance abuse can lead to psychological or physical dependence. People displaying psychological dependence on a drug will continue to use it even though it has
harmful effects. They need the drug for a sense of well-being and become preoccupied
with getting the drug if it is no longer available. However, they can still function without the drug. Psychological dependence can occur with or without physical dependence, also known as addiction. Addiction is a physiological state in which there is not
only a strong craving for the drug but also in which using the drug becomes necessary
to prevent an unpleasant withdrawal syndrome. Withdrawal symptoms vary depending on the drug, but they often include an intense desire for the drug and physical
effects generally opposite to those of the drug itself. Eventually, drug users may develop
tolerance, a condition in which increasingly larger drug doses are required to produce
the same effect (Sokolowska, Siegel, & Kim, 2002). With the development of tolerance,
many addicts need the drug just to prevent the negative effects of not taking it. However, most researchers believe that a craving for the positive effects of drugs is what keeps
addicts coming back to them (Ciccocioppo, Martin-Fardon, & Weiss, 2004; Everitt &
Robbins, 2005; George et al., 2001).
It may be tempting to think of “addicts” as utterly different from the rest of us, but
we should never underestimate the ease with which drug dependence can develop in anyone, including ourselves. Physical dependence can develop gradually, without our awareness. In fact, scientists believe that the changes in the brain that underlie addiction may
be similar to those that occur during learning (Nestler, 2001; Overton et al., 1999).
Substance Abuse
substance abuse The use of psychoactive drugs in ways that deviate from
cultural norms and cause serious problems for the user.
psychological dependence A condition in which a person continues drug
use despite adverse effects, needs the
drug for a sense of well-being, and becomes preoccupied with obtaining it.
physical dependence (addiction) Development of a physical need for a psychoactive drug.
withdrawal syndrome A set of symptoms associated with ending the use of
an addictive substance.
tolerance A condition in which increasingly larger drug doses are needed
to produce a given effect.
157
Psychoactive Drugs
FIGURE
4.9
Changing Views of Drugs
Total beer consumed (in milliliters)
The legal and social status of a drug can
vary across cultures and over time (Weiss
& Moore, 1990). For example, in the United
States cocaine was once a respectable,
commercially available drug; today it is illegal. And alcohol, which is legal in the
United States and many other nations, is
banned in countries such as Kuwait, Iran,
and Saudi Arabia.
400
350
All addictive drugs stimulate the brain’s “pleasure centers,” regions that are sensitive to
the neurotransmitter dopamine (Nestler, 2005). Neuron activity in these areas of the brain
produces intensely pleasurable feelings. It also helps generate the pleasant feelings associated with a good meal, a “runner’s high,” gambling, or sex (Grunberg, 1994; Harris &
Aston-Jones, 1995; Reuter et al., 2005). It is no wonder, then, that addictive drugs have
the capacity for creating tremendously rewarding effects in most people (Kelley &
Berridge, 2002).
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250
200
150
100
Drug effects are not determined by biochemistry
alone. The expectations we learn through experience with drugs and/or drug users also
play a role (Bartholow & Heinz, 2006; Cumsille, Sayer, & Graham, 2000; Siegel, 2005;
Stein, Goldman, & Del Boca, 2000). Several experiments have shown that research participants who consume alcohol-free drinks that they think contain alcohol are likely to
behave in line with their expectations about alcohol’s effects. So they tend to feel drunk
and to become more aggressive, more interested in violent and sexual material, and
more easily sexually aroused (Darkes & Goldman, 1993; George & Marlatt, 1986; Lang
et al., 1975; Lansky & Wilson, 1981). And because they know that alcohol impairs memory, these participants are more vulnerable to developing false memories about a crime
they witnessed on videotape (Assefi & Garry, 2003).
Expectations about drug effects develop in part as people watch other people react
to drugs (Sher et al., 1996), and these expectations can influence how much of a drug
they themselves consume (see Figure 4.10). What they see can differ from one individual and culture to the next, so drug effects vary considerably throughout the world
(MacAndrew & Edgerton, 1969). In the United States, for example, drinking alcohol is
commonly associated with uninhibited behavior, including impulsiveness, anger, violence, and sexual promiscuity. These effects are not seen in all cultures, however. In
Bolivia’s Camba culture, people sometimes engage in extended bouts of drinking a brew
that is 89 percent alcohol (178 proof). During these binges, the Camba repeatedly pass
out, wake up, and start drinking again—all the while maintaining friendly social relations. Other studies have shown that learned expectations also contribute to the effects
of heroin, cocaine, and marijuana (Robbins & Everitt, 1999; Schafer & Brown, 1991;
Smith et al., 1992).
In short, the effects of psychoactive drugs are complex and variable. Here, we consider several major categories of psychoactive drugs that people use primarily to
Expectations and Drug Effects
50
Cheers
Newhart
TV show watched
Alcohol-positive adjectives
Neutral adjectives
FIGURE
4.10
Expectancies and Alcohol
Consumption
People may drink more when their expectancies about the positive effects of alcohol have been primed. In this study,
some participants watched Cheers (a TV
show in which people enjoy themselves
while drinking alcohol) and were exposed
to adjectives associated with positive expectancies about alcohol. They later drank
more (nonalcoholic) beer than participants
who watched a non-alcohol-related show
and were not exposed to the alcoholpositive adjectives (Roehrich & Goldman,
1995).