Abnormal Psychology

Substance Use Disorders 387

abuse or dependence. The gateway hypothesis is not a blueprint for all users; rather,

it is a way to understand how people who abuse substances come to end up in that

situation. In addition, even when people do come to abuse drugs or be dependent on

them, they do not necessarily go through the specifi ed sequence. In fact, some people

with substance abuse problems had a reverse pathway: They started using harder

drugs before softer ones (George & Moselhy, 2005), for example, using marijuana

before using tobacco (Humfl eet & Haas, 2004).

Factors Associated With Progressing from Entry Drugs to Hard Drugs

Two factors are associated with progressing from using entry drugs to using hard

drugs:

1. Age. The younger a person is when he or she starts to use drugs or alcohol, the
   more likely he or she will be to abuse drugs later in life—and the less likely to
   decrease drug use or stop abusing drugs (D’Amico et al., 2001; Ginzler et al.,
   2003; Kandel & Yamaguchi, 1985; McGue & Iacono, 2005; Odgers et al.,
   2008; Sung et al., 2004);


2. Quantity. In general, the more drugs a person uses at the outset, the more likely
   he or she is to continue along the road to substance dependence (Bailey, 1992;
   D’Amico et al., 2001).

Note that the common liabilities model and the gateway hypothesis may both

be correct, at least in some cases. And, in fact, they may be conceptually related: An

underlying liability may lead some individuals to start experimenting with drugs

earlier, or more intensely, than others. This earlier or more intense use of drugs may

then lead some people with the underlying common liability to shift from entry

drugs to harder drugs.

Substance Abuse as a Category or on a Continuum?

According to DSM-IV-TR, substance abuse and substance dependence

are separate categories, and a habitual drug user is diagnosed with

either substance abuse or substance dependence (or, in theory, does not

meet the criteria for either diagnosis). However, some research suggests

that the abuse/dependence distinction is artifi cial and that a more mean-

ingful way to conceptualize harmful substance use, at least of alcohol,

is on a continuum of severity (Heath et al., 2003; Langenbucher et al.,

2004; Sher, Grekin, & Williams, 2005). According to this view, substance

use, abuse, and dependence vary not qualitatively but rather quantitatively,

with dependence on the extreme end of a continuum. This continuum is

defi ned by the frequency, quantity, and duration of use (see Figure 9.3).

The more frequent the use, the larger the quantity, and the longer the use

has been going on, the more likely the use is to become abuse. And increas-

ing frequency, quantity, or duration of use can push the diagnosis beyond

abuse to dependence.

According to the continuum approach, we would determine whether any of the

Beatles abused or was dependent on Preludin, for instance, based on how much,

how often, and for how long each of them took the stimulant. This approach quan-

tifi es severity in a way that the DSM-IV-TR criteria do not (O’Malley, Johnston, &

Bachman, 1999; H. A. Skinner, 1995).

Comorbidity

As we’ve noted in earlier chapters, many people with psychological disorders

abuse substances, particularly alcohol, marijuana, cocaine, and opiates (Lingford-

Hughes & Nutt, 2000). In a study specifi cally examining the prevalence of comor-

bid disorders among people with substance use disorders, almost half of those with

alcohol abuse or dependence also had another DSM-IV-TR disorder—and almost

three-quarters of those with drug abuse or dependence had another DSM-IV-TR

disorder (Regier et al., 1993). Common comorbid disorders include mood disorders

9.3 • A Continuum of Substance Use, Abuse,

and Dependence Substance use, abuse, and

dependence may be better conceptualized as occurring

on a continuum rather than as discrete categories. Where

an individual’s use falls on the continuum would be

determined by frequency, quantity, and duration.

Figure 9.3

y

g93

Recreational

use

Dependence

(has difficulty

not using the

substance)

Abuse

(use of the

substance creates

problems)