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ADHD in adults: A study of clinical
characteristics, impairment and comorbidity
TERJE TORGERSEN, BJØRN GJERVAN, KIRSTEN RASMUSSEN
Torgersen T, Gjervan B, Rasmussen K. ADHD in adults: A study of clinical characteristics,
impairment and comorbidity. Nord J Psychiatry 2006;60:38 /43. Oslo. ISSN 0803-9488.
In this study, we explored the clinical characteristics, impairment and comorbidity in a sample of
45 adult patients with attention-deficit/hyperactivity disorder (ADHD). The collection of data is
based on a naturalistic, retrospective approach using medical records documenting a
comprehensive assessment of the patients. The sample was severely impaired in terms of
academic achievement, employment and criminality, and had very high levels of comorbidity,
especially alcohol and drug abuse, antisocial personality disorder and depression. Despite a high
degree of contact with child psychiatric services in childhood, very few were diagnosed with
ADHD, and many had a long period of psychiatric treatment as adults before the ADHD
diagnosis was made. ADHD is in this sample of adults associated with severe impairment and
comorbidity, and the connection between impairment and lack of proper diagnosis and
treatment is discussed.
ADHD, adults, comorbidity, impairment, psychiatry.
Terje Torgersen, M.D., Helse Nord-Troendelag HF, Sykehuset Levanger, Department of
Psychiatry, NO-7600 Levanger, Norway, E-mail: Terje.Torgersen@helse-nordtrondelag.no;
Accepted 19 July 2005.
Until 1997, treatment of adult attention-deficit/hy-
peractivity disorder (ADHD) with stimulants was
forbidden in Norway. As evidence grew during the 1990s
about the efficacy of stimulant drugs on ADHD in
adults, so did the political pressure on health politicians
in Norway to ease the legal restrictions on stimulant
drug prescription. On this background, it was decided in
1997 to allow stimulant treatment in adults. A system to
secure adequate diagnosing, treatment and follow-up of
these patients was initiated and national guidelines were
issued, all under strict control by health authorities.
Adult patients with ADHD are a relatively new group of
patients for adult psychiatric healthcare, thus there is a
need for more knowledge about prevalence, clinical
characteristics and what good clinical practice is for
this sparsely recognized group of patients.
ADHD disorder is a prevalent disorder estimated to
affect 3/9% of school-aged children (1). From prospec-
tive studies of children with ADHD, there is a growing
body of evidence that the disorder persists into adult-
hood. Despite discussions around criteria for adults,
there seems to be an agreement that ADHD persists into
adulthood in as much as 30/60% of the cases (2, 3). The
childhood male-to-female ratios of clinic-referred sam-
ples range from 9:1 to 6:1, while the ratio for population-
based studies is approximately 3:1. During adolescence
and young adulthood, relatively more females are
affected (4).
Other challenges in estimating the prevalence rate of
adult ADHD are setting the diagnosis and deciding the
comorbidity. There is no objective test to verify a
diagnosis of ADHD. The diagnostic process can be
challenging, not the least due to uncertainty pertaining
to the retrospective assessment of childhood symptoms
(5). Adding to this complexity is the fact that comor-
bidity between ADHD and other psychiatric disorders is
very common. In a recent follow-up study, Biederman et
al. (6) found comorbidity of at least one psychiatric
disorder in as much as 34% of adult women with
ADHD, and 50% of men. Affective disorders, anxiety,
obsessive/compulsive disorder, personality disorder,
learning disabilities, and drug and alcohol abuse are
the most common comorbid disorders. As there are
many shared symptoms between ADHD and some
comorbid disorders, setting a proper diagnosis can often
be obscured. Some affective disorders are frequently
accompanied by difficulties in attention and concentra-
tion. Unstable affect, short temperedness and impulsiv-
ity are common characteristics of cluster B personality
disorders (7, 8).
Stimulant drugs like methylphenidate and dextroam-
phetamine have long been considered treatment of
#2006 Taylor & Francis DOI: 10.1080/08039480500520665
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choice for children with ADHD (9, 10). Current research
provides data indicating that stimulant treatment also is
effective in adults (11/14), but more data are required to
confirm long-term efficacy (15). As stimulants are
considered illegal drugs in many countries, treatment
of adults with these medications has not been common
practice.
The Department of Psychiatry, Levanger Hospital,
has a catchment area of 90,000 inhabitants, living in
small towns and rural districts. There were no other
psychiatric clinics or private practising psychiatrists in
this area (by October 2003). This indicates that every
adult patient in this catchment area being diagnosed
with ADHD and starting treatment with stimulants
during the 5-year study period has been seen by
professionals in our hospital, and this is corroborated
by comparing with the register of the regional committee
for hyperkinetic disorders.
The aim of the present study was to investigate
psychiatric morbidity, comorbidity and impairment in
patients diagnosed with ADHD and treated with stimu-
lants in a specific catchment area during the first 5-year
period after stimulant treatment was legalized for adults.
More knowledge is needed about this understudied and
in many cases severely impaired group of patients in
order to improve treatment and care.
Methods
Subjects
The subjects in this study were 45 patients who started
treatment with stimulants during the 5-year period: 34
men and 11 women. Mean (9
/standard deviation) age
was 28.39
/6.4, range 17/46 years. All of them fulfilled
the criteria for an ICD-10 diagnosis of F90.0 Hyperki-
netic disorder. The subjects were either referred from
family doctors to the psychiatric clinic, or they were
already in the patient population of the clinic (both
outpatient and inpatient clinic).
Diagnostic assessment
A comprehensive psychiatric examination was under-
taken for all patients included in the study by an
experienced psychiatrist. The assessment was done in
accordance to a diagnostic procedure/checklist made by
regional committees of specialists in adult ADHD. The
patients had to meet the research criteria for ICD-10
F90.0 Hyperkinetic disorder. Any occurrence of ICD-10
comorbid disorders like psychosis, bipolar disorder,
other affective disorders, anxiety disorder and drug
abuse had to be checked for, using a self-made checklist
for the most common comorbid disorders to ADHD. A
structured diagnostic interview like SCID or MINI was
not done consequently. Somatic and neurological exam-
inations were done, and a comprehensive laboratory
assessment (complete blood cell count, liver and kidney
function tests, glucose, thyroidea function tests) and an
electrocardiogram were completed. Whenever possible,
parents, teachers or other relevant persons were inter-
viewed about the patients’ childhood (B
/7 years old), to
confirm whether they met criteria for ADHD in child-
hood. In 88.9% (n
/40) of the patients, it was possible to
get this information. In 46.7% (n
/21) of the cases, a full
neuropsychological test battery was completed. Twelve
(26.7%) of the patients were examined with cerebral CT
or MRI, and 12 (26.7%) with EEG. When the clinicians
confirmed the diagnosis adult ADHD, a comprehensive
summary was sent to the regional committee describing
the diagnostic process and results. The patients com-
pleted the self-rating scales Symptom Checklist 90-items
(16) and a Symptom checklist for hyperkinetic disorders
(17). They also had to verify that they had not used
illegal drugs during the last 3 months. Whenever there
was any doubt about the patients being drug-free, this
was controlled by urine analyses. The regional commit-
tee decided in every case whether the patient met criteria
for the diagnosis, and could start treatment with
stimulants or not. If the criteria were met, the only
exclusion criteria for stimulant treatment was drug use
the last 3 months, ongoing serious suicidal behaviour
and ongoing psychosis.
All relevant information about the diagnostic assess-
ment and the patient history was documented in the
medical records at our clinic.
Procedure
The data for this study were collected from the medical
records at our clinic, where the comprehensive assess-
ments described in the previous passage are documen-
ted. A list of variables was made before screening the
medical records for information. A comorbid disorder
was only diagnosed if the information in the medical
record clearly confirmed the criteria for an ICD-10
diagnosis. The number of comorbid disorders is there-
fore likely to be a minimum estimate. Particularly data
on anxiety disorders and personality disorders (except
antisocial) often were too vaguely described in the
medical records to confirm the diagnosis. Current drug
abuse was diagnosed if the patient had met criteria for
drug abuse during the last year before starting treat-
ment. The data were statistically analysed by the SPSS
(Statistical Package for the Social Sciences, version 12).
The regional ethical committee has approved the study.
Results
Research criteria for ICD-10 F90.0 Hyperkinetic dis-
order require the presence of at least six symptoms of
attention-deficit, three symptoms of hyperactivity and
one of impulsivity. Forty-four patients met criteria for
attention-deficit, 43 patients met criteria for hyperactiv-
ity and 43 patients met criteria for impulsivity, thus no
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clear subgroups could be distinguished. This means that
44 patients (97.8%) also met the criteria for DSM-IV,
314.01 AD/HD combined type. All described a chronic
course of ADHD symptoms from childhood to adult-
hood. Twenty-nine (62.2%) had been in contact with
child psychiatric services (22 men, seven women), while
only eight (17.8%) had been diagnosed with ADHD in
childhood or adolescence (seven men, one woman).
Seven of these, all men, had been medicated with
stimulants in childhood, but only for short periods
(maximum 2 years). Nine (20%) had been diagnosed
with learning disability, 15 (33%) with conduct disorder
and four (8.9%) had epilepsy in childhood.
An overview of socio-demographic data and academic
achievement is presented in Table 1. Mean age for first
contact with adult psychiatric services was significantly
different for males vs. females (t
/2.25, PB/0.05). Mean
age for receiving the ADHD diagnosis as an adult was
26.3 years, and for starting with stimulants in adult life
28.3 years. Time from the first contact with adult
psychiatric services to starting with stimulant treatment
was 4.6 years for men and women. Most patients
(64.4%) had grown up with both parents. Only 20%
had fulfilled 12 years of education or more.
Data on vocational and civil status, as well as crime,
are summarized in Table 2. Only 15.6% were employed,
while 68.8% was getting some kind of social benefit.
Twenty-five (55.6%) were living alone.
Twenty-one (46.7%) patients had one or more crim-
inal sentences. Twelve (26.7%) had a sentence for
violence, ten (22.2%) for theft, eight (17.8%) for drug-
related crimes, and seven (15.6%) had a sentence for
drunk driving. Eleven patients had two or more different
types of criminal sentences. Thirty patients (66.7%) had
received psychiatric treatment as adults before being
diagnosed with ADHD.
Thirty-nine patients (86.7%) had lifetime comorbid
disorders as scored from the medical records by the time
of receiving the ADHD diagnosis, four had one comor-
bid disorder and 35 (77.8%) had two or more. Lifetime
major depression (53.3%), antisocial personality disor-
der (44.4%), alcohol abuse (46.7%), cannabis abuse
(51.1%) and amphetamine abuse (48.9%) were the
most frequent comorbid diagnoses. An overview of
current and lifetime comorbid diagnoses is presented
in Table 3. There were no differences between men and
women.
Discussion
This sample of predominantly ADHD combined type is
severely impaired according to academic achievement,
employment, criminality and comorbidity. Despite the
fact that the patients had a high degree of contact with
child psychiatric services in childhood, the ADHD
diagnosis was missed in most cases.
Table 1. Socio-demographic data and academic achievement.
Male (n/34), mean (s) Female (n/11), mean (s) Total (n/45), mean (s)
Age at first contact adult psychiatric services 24.8 (5.8) 20.5 (4.8) 23.7 (5.8)
Age when getting ADHD diagnosis as adult 26.7 (9.7) 24.9 (5.1) 26.3 (8.8)
Age starting stimulant treatment as adult 29.4 (6.5) 25.1 (5.1) 28.3 (6.4)
n(%)
Childhood/adolescence
Living with both parents 29 (64%)
Living with one parent 12 (31%)
Living in foster home 2 (4%)
Adopted at birth 5 (11%)
Academic achievement
Less than 9 years education 3 (7%)
Between 9 and 12 years of education 33 (73%)
12 years of education or more 9 (20%)
s, standard deviation.
Table 2. Vocational status, civil status and criminality at start
of treatment with stimulants (n
/45).
n(%)
Employed 7 (16%)
Student 7 (16%)
Transitional benefit* 2 (4%)
Sick pay 3 (7%)
Vocational rehabilitation 10 (22%)
Rehabilitation allowance 11 (24%)
Disability pension 5 (11%)
Social assistance 4 (9%)
Living alone 25 (56%)
Living with partner 20 (44%)
Criminal activity
One or more criminal sentences 21 (47%)
Two types$of sentences or more 11 (24%)
$Violence 12 (27%)
$Theft 10 (22%)
$Drug-related crime 8 (18%)
$Drunk driving 7 (16%)
*Benefit to single parents.
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The predominant ADHD subtype in this sample was
the combined type. There was a high comorbidity
between ADHD and antisocial personality disorder as
well as alcohol and drug abuse. The number of subjects
fulfilling criteria for antisocial personality disorder was
twice as high as reported in other studies (3, 18, 19).
Comorbid alcohol and drug abuse are also high
compared to previous studies, showing occurrence of
comorbid alcohol abuse up to 36% (20) and comorbid
drug abuse between 27% and 46% (21). The relationship
between ADHD combined type and antisocial person-
ality disorder is consistent with findings from previous
studies on children and adults (22).
Our results indicate that a proper diagnosis of ADHD
has been missed in childhood in a substantial proportion
of the patients, meaning that these patients also did not
receive proper treatment with stimulant drugs in spite of
the high frequency of contact with child psychiatric
services. The most probable reason for this is a lack of
clinical awareness for ADHD among Norwegian child
psychiatric services when these patients were growing up.
This lack of identification and treatment is recently
described in another study (6), and in previous studies
(23, 24). It is an important finding that the average time
from first contact with adult psychiatric services to
treatment with stimulants is 4.6 years, indicating that the
lack of awareness also was significant in adult psychia-
tric services. Reasons for this finding can be the fact that
stimulants was forbidden for adults until 1997, and that
the ADHD diagnosis was neglected in adult psychiatric
services.
The women in this sample were significantly younger
than the men when they first got in contact with adult
psychiatric services, and also when being diagnosed and
starting treatment. Hyperactivity and impulsivity, con-
duct disorders and antisocial personality disorder, and
alcohol and substance abuse are often referred to as
externalizing symptoms. In this study of referred adults,
there were no significant gender differences in externa-
lizing symptoms. One interpretation is that the women in
this sample have more severe psychiatric problems,
resulting in earlier referral to psychiatric services (4,
25/27). For referred samples, the differences seem to be
smaller (4, 6), while gender differences in symptoms are
more typical for non-referred samples.
The total number of patients with comorbid disorders,
especially the number of patients having two or more
comorbid disorders in this study were high compared to
most previous studies (6, 21, 28, 29); 86.7% of the
patients in our study had at least one comorbid disorder.
Many previous studies have shown significant impair-
ment in samples of adult ADHD (18, 28, 30), and even
worse in the presence of comorbid psychiatric disorders
(31). The subjects in our study have an even higher
degree of impairment. Data on educational achievement
showed that only 20% had 12 or more years of
education, in contrast to 84% in the general population
in Nord-Troendelag county (32). These figures are
considerably lower than other studies have shown (22,
28, 33). The frequency of current employment was also
very low (15.6%), and considerably lower than other
studies have shown (33/36). By contrast, the general
unemployment rate in Nord-Troendelag county in
November 2003 was 3.6 (32).
One might speculate that the severe impairment seen
in our sample in terms of severity of symptoms and
comorbidity is, at least partly, due to lack of proper
treatment in childhood, although our study design does
not allow for any conclusions regarding this. There is,
however, some circumstantial evidence for this view.
Alcohol and drug abuse are by themselves unfavourable
indices for social impairment, and predicts low function-
ing on many aspects of life. ADHD is a risk factor for
drug abuse (2, 37). However, recent studies indicate that
Table 3. Current and lifetime comorbidity (n/45).
Current, n(%) Lifetime, n(%) Lifetime, male, n(%) Lifetime, female, n(%)
Major depression 4 (9%) 24 (53%) 17 (50%) 7 (64%)
Bipolar disorder 1 (2%) 3 (7%) 2 (6%) 1 (9%)
Panic disorder 1 (2%) 6 (13%) 3 (9%) 3 (27%)
Social phobia 8 (18%) 6 (18%) 2 (18%)
Post-traumatic stress disorder 2 (4%) 2 (6%)
Schizophrenia 2 (4%) 2 (6%)
Other psychoses 1 (2%) 1 (3%)
Tourette syndrome 1 (2%) 1 (3%)
Mentally disabled 2 (4%) 2 (6%)
Learning disabilities 10 (22%) 7 (21%) 3 (27%)
Antisocial personality disorder 20 (44%) 15 (44%) 5 (45%)
Alcohol* 15 (33%) 21 (47%) 17 (50%) 4 (36%)
Opiates* 2 (4%) 7 (16%) 6 (18%) 1 (9%)
Cannabis* 16 (36%) 23 (51%) 17 (50%) 6 (55%)
Amphetamine* 15 (33%) 22 (49%) 17 (50%) 5 (45%)
*Current
/last year.
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treatment with stimulants in childhood reduces the risk
for later drug abuse considerably, especially in adoles-
cence but also in adulthood (38). A German study (39)
reported a clinically and statistically significant reduc-
tion in the risk of drug use disorders in young adults who
were treated previously with methylphendidate. The
authors also found a linear relationship between risk
reduction and duration of stimulant treatment. There
are many theories why stimulant treatment reduces the
risk for drug abuse, and one is that stimulants indirectly
reduce the risk by diminishing conduct symptoms (40),
as conduct disorders and later antisocial personality
disorder are predictors of drug abuse. Another possible
explanation is that stimulant treatment reduces ADHD
symptoms, demoralization, poor self-esteem and aca-
demic and occupational failure, factors associated in-
dependently with risk for drug abuse (41/43).
In a review study, Hechtman & Greenfield (10) found
that children treated with stimulants for as long as
2 years showed improvement in ADHD symptoms,
comorbid oppositional defiant disorder, and academic
and school functioning. Follow-up periods into adult-
hood showed that stimulant treatment in childhood also
was beneficial for social skills and self-esteem. Higher
doses and longer treatment period predicted less comor-
bidity and better social functioning.
ADHD in adults have striking similarities with
paediatric samples regarding psychiatric and cognitive
impairment (6). If the effect of stimulants is similar in
paediatric and adult samples, as some studies suggest
(13), there is reason to believe that adult patients also
will have this long-term positive outcome. There is a lack
of studies on long-term outcome of stimulant treatment
in adults, and more research is needed before the long-
term effect is established. Particularly there is a lack of
evidence for the long-term effect of stimulants on
functional impairment, not only on symptoms.
There are some limitations to the present study. First
of all, the subjects were clinically referred psychiatric
patients. One would expect the symptom load to be high
in this population, and our results cannot be generalized
to other populations. Another limitation pertains to the
retrospective nature of diagnostic assessment, as a
diagnosis of ADHD requires the presence of symptoms
before 7 years of age. Although retrospective assessment
of psychopathology is non-optimal in adult psychiatry,
there are studies indicating that a retrospective diagnosis
of childhood-onset ADHD can be made reliably (21, 44)
Furthermore, the diagnostic criteria were verified by
corroborative information from persons with knowledge
about the patients’ childhood in a substantial number of
our subjects. Another weakness is the lack of consequent
use of structured diagnostic interviews.
The degree of functional impairment and presence of
comorbid disorders in our study seems to be surprisingly
high. It should be born in mind, however, that a
comorbid disorder was not endorsed unless the record
clearly showed that the criteria were fulfilled. This strict
procedure is more likely to yield an underestimate of the
true level of comorbidity rather than the opposite.
In conclusion, our results clearly suggest that ADHD
in adult psychiatric patients is related to a high degree of
comorbidity and functional impairment, and clinicians
must bear this in mind when diagnosing these patients
and planning treatment. Future studies should focus on
the long-term efficacy of stimulant treatment in these
patients, on symptoms, comorbidity and functional
impairment.
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Terje Torgersen, M.D., staff psychiatrist, Helse Nord-Troendelag HF,
Sykehuset Levanger, Department of Psychiatry, NO-7600 Levanger,
Norway.
Bjørn Gjervan, Cand.Polit., research associate, Helse Nord-
Troendelag HF, Sykehuset Levanger, Department of Psychiatry, 7600
Levanger, Norway.
Kirsten Rasmussen, Ph.D., professor, Department of Psychology,
Norwegian University of Science and Technology, Dragvoll, 7491
Trondheim, Norway.
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