Comorbid Psychiatric Disorders in Adults
with ADHD
by Russell A. Barkley, Ph.D., and Kevin R.
Murphy, Ph.D.
This article was reprinted with permission
from The ADHD Report, 15 (2) April 2007.
Adults with ADHD have been found in prior
studies to have a greater risk for various
psychiatric disorders. Chief among these are
oppositional defiant disorder (ODD) and
conduct disorder (CD). Approximately 24-35%
of clinic-referred adults diagnosed with
ADHD have ODD and 17-25% have CD, either
currently or over the course of their earlier
development (Barkley,Murphy, & Kwasnik, 1996;
Biederman, et al., 1993; Murphy & Barkley,
1996;Murphy, Barkley, & Bush, 2002; Spencer,
2004). These figures for clinic-referred
adults are below those reported in studies of
ADHD children, particularly studies of
hyperactive children followed to adulthood,
where levels of ODD and CD may be double or
triple these rates reported for adults
diagnosed with ADHD (see Barkley, 2006, for a
review; Barkley, Fischer, Edelbrock, &
Smallish, 1990; Fischer, Barkley, Smallish, &
Fletcher, 2002; Weiss & Hechtman, 1993).
Among parents of children having ADHD who
also meet criteria for ADHD, disruptive
behavior disorders are also significantly
more common (McGough et al., 2005; Minde, et
al., 2003). For instance, one study found
that 53% have had ODD and 33% have had CD
sometime in their lives (Biederman et al.,
1993), figures closer to those seen in
follow- up studies of hyperactive or ADHD
children. Antisocial Personality Disorder is
often an associated adult outcome in a large
minority of those children or adolescents who
have both ADHD and CD; thus it is not
surprising to find that 7-44% of
clinic-referred adults diagnosed with ADHD
also qualify for a diagnosis of this
personality disorder (Biederman et al., 1993;
Shekim, Asarnow, Hess, Zaucha, & Wheeler,
1990; Torgersen, Gjervab, & Rasmussen, 2006).
Even among those who do not qualify for this
diagnosis, many receive higher than normal
ratings on those personality traits
associated with this personality disorder
(Tzelepis, Schubiner, & Warbase, 1995).
Substance dependence and abuse are known to
occur to a more frequent degree among
hyperactive or ADHD children who develop CD
by adolescence or Antisocial Personality
Disorder by adulthood (Barkley, 2006;
Tercyak, Peshkin, Walker, & Stein, 2002).A
recent study of a large general population
sample likewise found an association between
ADHD and antisocial disorder (Kessler, et
al., 2006). Adults clinically diagnosed with
ADHD seem to be no exception to this rule
linking ADHD, antisocial activities, and drug
use disorders. Studies have found lifetime
rates of alcohol dependence or abuse
disorders ranging between 21% and 53% of
adults diagnosed with ADHD, whereas 8-32% may
manifest some other form of substance
dependence or abuse disorder.
Tzelepsis and colleagues (1995) reported that
36% of their 114 adults with ADHD had
experienced dependence on or abuse of
alcohol, 21% for cannabis, 11% for cocaine or
other stimulants, and 5% for poly-drug
dependence. Moreover, at the point of their
initial evaluation, 13% met criteria for
alcohol dependence or abuse within the past
month. Likewise, Torgersen and colleagues
(2006) found that 45% of their sample of 45
adults with ADHD in Norway had lifetime
alcohol abuse (33% currently), 51%for
cannabis (36%currently), 49% for amphetamines
(33% currently), and 16% for opiates (4%
currently). Parents of ADHD children who have
ADHD have also been found to have elevated
risks for substance use disorders, primarily
involving alcohol (McGough et al., 2005;
Minde et al., 2003).
More recently, cigarette smoking has shown an
association with increased symptoms of ADHD
in a general population sample of adults
(Kollins, McClernon, & Fuemmeler, 2005)
consistent with longitudinal studies of ADHD
children that find them to carry an increased
risk for smoking by adolescence (Milberger,
Biederman, Faraone, Chen, & Jones, 1997;
Molina, Smith, & Pelham, 1999; Tercyak,
Peshkin,Walker,&Stein, 2002; Whalen, Jamner,
Henker, Delfino, & Lozano, 2002). The highest
risks for substance use disorders appears to
be among those adults with ADHD who may also
have comorbid CD, antisocial personality
disorder, or bipolar disorder (Wilens, 2004).
Approximately 25% of children with ADHD have
an anxiety disorder (see Barkley, 2006;
Tannock, 2000). Most studies of ADHD in
adults likewise find an over-representation
of these disorders. The corresponding figure
among adults is 24% to 43% for Generalized
Anxiety Disorder and 52% for a history of
Overanxious Disorder (Barkley et al., 1996;
Biederman et al., 1993; Minde et al., 2003;
Shekim et al., 1990). Torgersen and
colleagues (2006) found that 13% of their
adults with ADHDhad lifetime panic disorder
and 18% lifetime social phobia. But not all
studies of ADHD in adults have found it to be
associated with anxiety disorders. Our own
prior research (Murphy & Barkley, 1996;
Murphy et al., 2002) did not find anxiety to
be over-represented in our clinical sample of
adults with ADHD. Neither did Roy-Byrne and
colleauges (1997) in comparison to a clinical
control group. The prevalence of anxiety
disorders among adults with ADHD who are
relatives of clinically diagnosed ADHD
children, however, is 20%, again suggesting
some comorbidity with ADHD (Biederman et al.,
1993). Parents of children with ADHD who
themselves have ADHD likewise have
significantly more anxiety disorders than do
those parents in a control group (McGough et
al., 2005; Minde et al., 2003). In
conclusion, there is some inconsistency in
findings concerning the comorbidity of ADHD
in adults with adult anxiety disorders, but
the weight of the evidence favors some
association, as it does in childhood ADHD.
Major depression does seem to have some
inherent affinity with ADHD children,
especially those having CD (Angold, Costello,
& Erkanli, 1999). Similarly, approximately
16% to 31% of adults meeting ADHD diagnostic
criteria also have Major Depressive Disorder
(Barkley et al., 1996; Biederman et al.,
1993; Roy-Byrne et al., 1997; Tzelepis et
al., 1995). Indeed, one study of Norwegian
adults with ADHD reported a lifetime
prevalence of 53% and current prevalence of
9% for major depression (Torgersen et al.,
2006). Dysthymia, a milder form of
depression, has been reported to occur in
19-37% of clinic-referred adults
diagnosed with ADHD (Murphy et al., 2002;
Roy-Byrne et al., 1997; Shekim et al., 1990;
Tzelepis et al., 1995). Some follow-up
studies have not been able to document an
increased risk for depression among
hyperactive children followed to adulthood
(see earlier). However, the Milwaukee
follow-up study of a large sample of
hyperactive children found a prevalence of
28% for
major depression by young adulthood- a
finding quite consistent with the studies on
clinic-referred adults diagnosed with ADHD.
Even so, a few studies comparing
clinic-referred ADHD adults to adults seen at
the same clinic without ADHD have not found a
higher incidence of depression among the ADHD
adults (Murphy & Barkley, 1996; Roy-Byrne et
al., 1997). Rucklidge and Kaplan (1997)
reported one of the few studies of women with
ADHD and found them to report more symptoms
of depression, anxiety, stress, low
self-esteem, and a more external locus of
control than did women in the control group
but psychiatric diagnoses were not reported
in this study. In a study of parents of ADHD
children who also have ADHD,
Minde et al. (2003) did not find a greater
prevalence of major depression relative to a
control group of parents (15% vs. 8%), but
the study used small samples limiting its
representation of parents with ADHD and its
statistical power to detect group differences.
It also did not find elevated rates of
antisocial personality disorder which, as
discussed above for CD, might be a potential
moderator between ADHD and depression. In
contrast, the much larger study of ADHD
parents having ADHD children by McGough and
colleagues (2005) did find greater mood
disorders than in their comparison group. In
general, some relationship between ADHD in
adults and risk for depression appears to
exist, as it does in children with the
disorder.
The relationship of ADHD in adults to bipolar
disorder has not been well-studied. Follow-up
studies of children with ADHD into adulthood
typically do not report elevated rates of
this disorder by adult outcome (Barkley,
2006; Barkley, Fischer, Smallish, &
Fletcher, 2002). But other studies of
children with ADHD have found elevated risk
(6-27%) (Barkley, 2006; Biederman, 2004) for
bipolar disorder. Studies by Biederman and
colleagues have also reported an elevated
risk for this disorder in clinic-referred
adults (11-14%) (Biederman, 2004). In the
Norwegian sample studied by Torgersen and
colleagues, (2006), the prevalence was 7% for
lifetime disorder and 2% currently;
comparable to follow-up studies of
hyperactive/ADHD children into adulthood
(Fischer et al., 2002) and close to the base
rate for the general population. The
relationship of ADHD to bipolar disorder in
adults is therefore in need of more research
before some confidence can be placed in this
pattern of comorbidity.
Obsessive-Compulsive Disorder (OCD) was
initially reported to occur in 14% of
clinically diagnosed adults with ADHD (Shekim
et al., 1990). However, Tzelepis and
colleagues (1995) were unable to replicate
this finding and reported only4%of their
adults met diagnostic criteria for OCD.
Roy-Byrne and colleagues (1997) likewise
reported a 4.3-6.5% prevalence rate, which
was not significantly different from their
clinical control group. Spencer (1997) found
that OCD was more common (12%) only among
those adults with a comorbid tic disorder
whereas the figure for those ADHD adults
without tics was approximately 2%. Thus, OCD
does not appear to be significantly
associated with ADHD in clinic-referred
adults unless tic disorders or Tourette
Syndrome are also present.
To summarize, past research suggests a higher
than expected association between ADHD in
adults and comorbid ODD, CD, antisocial
personality disorder, substance use
disorders, and probably depressive disorders
(major depression and dysthymia). The link
between ADHD and substance use disorders is
likely mediated by the association of ADHD
with CD or antisocial personality. So may
be the link between ADHD and major
depression. The relationship between adult
ADHD and adult anxiety disorders and between
ADHD and bipolar disorder is less well
established. There seems to be no elevated
risk for OCD among adults with ADHD.
COMORBID PSYCHIATRIC DISORDERS IN THE UMASS
PROJECT
In several previous issues, we have reported
various results from a large study of adults
with ADHD. The results of our work in its
entirety will appear later this year in a new
book entitled The Science of ADHD in Adults:
Clinic-Referred Adults vs. Children Grown Up
(Barkley, Murphy, & Fischer, Guilford, in
press). This project constitutes one of the
most comprehensive evaluations of adults with
ADHD. In this project, we extensively
evaluated146 adults with ADHD on numerous
measures of adaptive functioning across many
domains of major life activities. We compared
them to both a
community control group of 109 adults and a
clinical control group of 97 adults seen at
the same ADHD clinic but not diagnosed with
the disorder. These adults had a mean age of
32 to 37 years, depending on the group, with
47-68% of each group being male.
For this article, we report on the
comorbidity for psychiatric disorders in our
groups using the Structured Clinical
Interview for DSM-IV Disorders (SCID;
Spitzer, Williams, Gibbon, & First, 1995).
The results are shown in Table 1 (not shown
here). We found that both the ADHD group and
the clinical control group were more likely
to have experienced major depression either
currently, in the past, or at any time in
their life compared to the clinical control
group. The occurrence of depression in the ADHD
group is comparable to that seen in some
prior studies and is certainly elevated over
that seen in the Community control group
(Marks, Newcorn, & Halperin, 2004; Spencer,
Wilens, Biederman, Wozniak, & Harding-
Crawford, 2000). But it was not elevated over
that seen in other non-ADHD patients
presenting to the same clinic as the ADHD
adults. It is therefore not clear from our
results that major depression is a specific
comorbidity for ADHD in adults or whether it
reflects a nonspecific association with
clinic-referral status.
The fact that ADHD
relatives of children with ADHD also have
elevated rates of depression does suggest
some familial/ genetic association between
the disorders, as does the literature on
comorbidity between the disorders in
epidemiological samples of children (Angold
et al., 1999). Our Clinical control group
certainly had elevated symptoms of ADHD
relative to the control group even though
they were not eventually diagnosed in this
study as ADHD. The risk for major depression
may therefore be elevated in adults having
elevated levels of ADHD symptoms even though
they may not qualify for the diagnosis on all
diagnostic criteria or in clinical judgment.
The results of Roy-Byrne and colleagues
(1997) are supportive of such an
interpretation given that they also found
equally elevated levels of major depression
in their clinical control groups and ADHD
group. So there may be true comorbidity
between these two dimensions of
psychopathology that would be consistent with
the present findings of elevated rates of
depression in both our ADHD and Clinical
controls.
But the difference between ADHD and
the Clinical controls does not rise to the
level of significance. We did find an
increased risk for current dysthymia in the
ADHD group relative to both the Clinical and
Community control groups. The Clinical
control group also showed a higher risk for
dysthymia than the Community control group
but not to the degree shown in the ADHD
group. Rates of past dysthymia were not
significantly different among the groups, but
because of the greater risk of current
dysthymia, both the ADHD and Clinical groups
had a significantly greater risk of having
ever had dysthymia than did the Community
group.
Past studies found that 17-37% of adults with
ADHD experienced dysthymia (see above), and
our resultsaccord with the higher end of this
range (37% current dysthymia)-a figure nearly
three times as great as that seen in the
Clinical control group. Thus, not only is the
risk of major depression elevated in adults
with ADHD, but this iseven more so with its
milder variant of dysthymia. Such an
association of ADHD with risk for depressive
disorders was recently found in two large
epidemiological studies of a general
population sample of adults suggesting that
there is true comorbidity between ADHD and
these disorders (Kessler et al., 2006;
Secnik, Swensen,&Lage, 2005) just as there is
in childhood epidemiological samples (Angold
et al., 1999).
As in some past studies discussed above, we
also found a greater risk of generalized
anxiety disorder currently in adults with
ADHD to about the same extent as these past
studies and in keeping with the risk reported
in some studies of children with ADHD (around
25%). As with major depression, this rate of
comorbidity was not significantly
different from the rate seen in the Clinical
control group (14%), with both groups
differing from the low rate seen in the
Community control group (1%). The rate for
past occurrence of this disorder did not
differ among the groups and was exceptionally
low. But as a result of current anxiety
disorder, the lifetime occurrence of this
disorder was also elevated in both the ADHD
and Clinical control groups. Such a result
again could suggest that generalized anxiety
disorder may not be so much a specific
elevated risk for those with ADHD as a more
general risk for clinic-referred samples.
Similar results were reported by Roy-Byrne
and colleagues (1997). But both studies would
also be consistent with the view, noted
above, that the elevated level of ADHD
symptoms in the control group likely elevates
their risk of anxiety disorder even though
such cases are not eventually diagnosed as
meeting all diagnostic criteria for ADHD. An
elevated association between anxiety
disorders and ADHD has been found in
epidemiological studies of children (Angold
et al., 1999) implying some elevated risk of
comorbidity even after controlling for
associations with a third disorder, such as
depression. It has also been recently
reported in two large epidemiological studies
of adults (Kessler et al., 2006; Secnik et
al., 2005). In short, the greater the level
of ADHD symptoms that exist in a patient, the
greater the risk for depression and anxiety
disorders.
This still does not explain why longitudinal
studies of hyperactive/ ADHD children do not
show elevated rates of anxiety disorders at
adult outcome. That is a finding in need of
clarification. We did not find any elevated
association of adult ADHD with bipolar
disorder in comparison to either the Clinical
or Community control groups. This is
consistent with follow-up studies of children
with ADHD to adulthood, with some studies of
clinic-referred adults discussed earlier, and
with the large epidemiological study of
Kessler and colleagues (2006). Our results
and those of these other studies therefore
disagree with those by Biederman (2004;
Spencer et al., 2000) and the recent
epidemiological study by Secnik and
colleagues (2005) that reported such an
elevated risk for comorbidity (4.5% vs.
0.6%). Why these discrepancies across studies
exist is not clear but continues to leave
this association of disorders in some doubt.
Consistent with all prior studies of adults
with ADHD, whether using clinic-referred or
epidemiologically derived samples, we did not
find an increased risk for OCD in our ADHD
group relative to our Clinical or Community
groups. We did, however, find such an
elevated risk in our Clinical control group
relative to the two other groups. The
totality of results to date therefore
indicates no elevated risk of OCD in adult
patients with ADHD.
Both our ADHD group and Clinical control
group demonstrated an elevated risk for
alcohol dependence or abuse disorders
currently (18 and 12%, respectively) compared
to the Community control group, and as a
consequence also showed an elevated rate of
lifetime risk for these disorders. Such
findings are in keeping with prior studies
showing that adults with ADHD do have higher
rates of such disorders compared to community
control groups (Murphy et al., 2002). But so,
too, do clinic-referred adults who do not
qualify for a clinical diagnosis of ADHD
(Roy-Byrne et al., 1997). Once again, such
findings may suggest that increased alcohol
use disorders may not be a specific
comorbidity for adult ADHD as for adult
clinic-referral status. But they could also
be consistent with some association between
elevated ADHD symptoms and risk for these
disorders given such elevated symptoms in the
Clinical control group. Supporting this
latter interpretation were the findings of
two large epidemiological studies (Kessler et
al., 2006; Secnik et al., 2005). But this
association with substance use disorders may
depend on comorbidity with a third set of
disorders, that of ODD, CD, and antisocial
personality as discussed above.
This point was supported in a study of
non-referred ADHD relatives of ADHD children
(McGough et al., 2005) that showed an initial
association of ADHD with substance use
disorders. McGough and colleagues (McGough et
al., 2005) assessed psychiatric comorbidity
in the parents of children with ADHD who were
participating in a study of the genetics of
the disorder. The study evaluated 435 parents
who completed rating scales and structured
diagnostic interviews. Parents who also had
ADHD were more likely to have experienced
psychopathology over their lifetime with 87%
(versus 64% of non-ADHD parents) having at
least one other disorder and 56% (versus 27%
of non-ADHD parents) having at least two
other disorders. Specifically, ADHD was
associated with higher rates of disruptive
behavior disorders, substance use, and mood
and anxiety disorders. Males were more likely
to have exhibited disruptive behavior
disorders while female sex and ODD increased
the risk of anxiety and depression. When male
sex, disruptive behavior, and socioeconomic
status were controlled, ADHD did not confer a
higher risk for substance use disorders,
suggesting that these factors, and
not ADHD itself, convey the higher risk for
substance use disorders.
We also found an increased risk for current
cannabis dependence and abuse disorders in
our ADHD group compared to our Community
group, consistent with our prior study
(Murphy et al., 2002). But this risk was also
elevated in the Clinical control group as
well, which did not differ from the ADHD
group in this respect. But the ADHD group did
show an increased rate of past such disorders
compared to both control groups. As a
consequence, the ADHD group had an elevated
risk for lifetime occurrence of these
disorders compared to both control groups.
Our findings suggest a specific comorbidity
between ADHD and cannabis use disorders. As
we discuss in our book in the chapter on
health and lifestyle risks, the ADHD group
had an increased likelihood of smoking and
that served to mediate this risk for greater
cannabis use. In other words, it is among the
adults with ADHD who smoke cigarettes that
one is likely to find the increased risk for
cannabis use as well.
There were two other disruptive behavior
disorders that were prominent in the
literature noted above on comorbidity with
ADHD: ODD and CD. The SCID does not have
modules for these particular disorders. But
we did obtain reports of these symptoms on
our self-report rating scales of
retrospectively recalled childhood ADHD. From
these scales, we were able to determine if
participants met symptom thresholds for these
two disorders retrospectively sometime during
childhood. The proportion of each group
having ODD was ADHD = 50% (N = 71), Clinical
= 18% (17), and Community = 2% (2) (χ2 =
78.96, df = 2, p < .001).
Consistent with all prior studies discussed
above, the ADHD group had a markedly greater
risk for ODD than did either of the two
control groups, making it clear that ADHD and
ODD are specifically associated with each
other. The Clinical control group also had a
greater rate than the Community group but
fell well below that seen in the ADHD group.
Concerning past occurrence of CD,we found
that 25% of the ADHD group and 16% of the
Clinical group qualified for this diagnosis,
retrospectively, while the rate for the
Community control group was 7%. The ADHD and
Clinical groups
did not differ significantly from each other
in this respect, but both differed from the
Community control group. Our results are
certainly consistent with past studies
comparing ADHD and community control samples
which found a higher risk for CD in
association with ADHD, but they suggest that
this risk is also elevated in non-ADHD clinic
referred samples, though not to the degree
seen in ADHD samples. Again, this may have to
do with the elevated occurrence of ADHD
symptoms even in the Clinical control group.
Epidemiological studies have also found an
association of ADHD with these other
disruptive disorders (Kessler et al., 2006;
Secnik et al., 2005), as did the study of
non-referred ADHD adult relatives among ADHD
children reported by McGough and colleagues
(2005).
To summarize, for the most part, our results
are relatively consistent with past studies
on comorbidity. We found that relative to
Community controls, ADHD was associated with
an increased risk for depression, dysthymia,
generalized anxiety disorder, alcohol
and cannabis dependence and abuse disorders,
and a childhood history of ODD and CD. But it
was not associated with any higher risk for
OCD or for bipolar disorder. Dysthymia,
cannabis use disorders, and ODD were also
significantly elevated in the ADHD relative
to the Clinical control group, implying that
these disorders may be specifically
associated with ADHD beyond their elevated
association with clinic-referred adults not
having ADHD.
For practitioners, these results mean that
additional treatments will need to be added
to the management package developed for
clinic-referred adults with ADHD that focus
on the comorbid disorder. Current treatments
for ADHD, such as the stimulants and
atomoxetine, are quite effective for ADHD
management but do not treat comorbid mood
disorders. These disorders will require
separate pharmacological and
cognitive-behavioral management and therapy.
Some research suggests that comorbid anxiety
disorders may be associated with poor
stimulant response though others have not
necessarily found such an association
(Connor, 2006). Recent evidence (personal
communication, Eli Lily Co.) suggests that
atomoxetine does not adversely affect anxiety
in children with comorbid ADHD and anxiety
disorders and may result in significant
improvements in anxiety symptoms. This work
needs to be replicated with adults with ADHD
having anxiety disorders. Certainly, comorbid
drug use disorders will require additional
psychosocial detoxification and/or
rehabilitation treatments apart from those
treatments addressing the adult's ADHD.We
believe these results show that comorbidity
in adults with ADHD is the norm, not the
exception, and that such comorbid disorders
have a significant impact on tailoring
treatment packages for the adult with ADHD.
Dr. Barkley is Editor of the ADHD Report and
is a Research Professor of Psychiatry, State
University of New York Upstate Medical
Center, Syracuse, NY and a Clinical Professor
of Psychiatry, Medical University of South
Carolina, Charleston, SC.
Dr. Murphy is on the Editorial Board of The
ADHD Report and is Director of the Adult ADHD
Center of Central Massachusetts,
Northborough, MA.
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