ADHD Long-term Outcomes: Comorbidity, Secondary Conditions, and Health Risk Behaviors
June 9, 1999
Rachel G. Klein, Ph.D.
Joseph Biederman, M.D.
Estimates of comorbidity, secondary conditions, and health risk behaviors among those with Attention-Deficit/Hyperactivity Disorder (ADHD) are quite high and range from 30 to 60 percent for highly comorbid conditions. ADHD is a very prevalent childhood disorder with a number of commonly comorbid conditions that present or develop in time with significant additional social, learning, and psychological impairment. Little rigorous scientific study of comorbidity etiology, risk factors, or prevention has been completed and the studies available have relied heavily on clinic-based populations rather than on population-based sampling. Comorbid conditions and health risk behaviors associated with ADHD are often not identified or treated appropriately and come with significantly more social cost burden, increased risk for poor educational attainment, and compromised social integration. A public health perspective must be applied to this disorder in a manner that acknowledges and addresses the high risk for comorbidity, secondary conditions, and participation in significant health risk behaviors associated with impulsive and inattentive behavior.
In an effort to delineate the issues in the long-term outcomes for ADHD individuals as well as the gaps in such research, a one-day meeting was hosted by Division of Birth Defects, Child Development, and Disability and Health (proposed)/NCEH with two researchers experienced in the long-term study of ADHD and the NCEH ADHD work group comprised of DDB staff. Prior to the meeting Division of Birth Defects, Child Development, and Disability and Health (proposed) had identified and provided to all participants an outline of the specific issues and questions related to comorbidity and ADHD from a lifespan perspective. The questions and discussion that ensued resulted in the following points during this one day meeting:
Please note that all answers are the summarized sentiments of the participants invited to this meeting and not those of the CDC. Statements herein are not, in any way, to be interpreted as promissary for inclusion in any ADHD research agenda setting nor are they ADHD policy statements by the Centers for Disease Control and Prevention, National Center for Environmental Health. This meeting was exploratory in nature and the results are provided here in an attempt to share the most information with the public.
Q1. What are the most costly, common comorbid disorders and health risk behaviors associated with ADHD (see list)?
Disruptive Behavior Disorders
Health Risk Behaviors:
Abnormal risk-taking and impulsive behaviors
Risk for injury (what types)
In presentations of the long-term research/follow-up from Drs. Klein and Biederman, the following additional points regarding comorbidity were noted:
Increased likelihood of adult psychopathology to include continued impairment attributable to ADHD was present in a significant proportion of subjects; however, remission is hard to estimate given varied operationalizations of the criteria for ADHD and the question of whether impairment in life functioning should be the marker for adult ADHD. It is commonly estimated that at least half of children with ADHD will chronically have the disorder, with some estimates as high as 85% of those children retaining the impairments associated with the disorder well into adulthood.
Other comorbidity, secondary conditions, and health risk behaviors seen in their follow-up studies included:
Antisocial Personality Disorder (ASPD);
Substance Use Disorder (SUD);
Conduct Disorder (CD) which is gender-specific (Biederman reported 22% of boys exhibiting CD-like antisocial behavior while only 8% of the girls did so);
A significant rate of major depression among boys, and significantly higher rates of anxiety among both boys and girls;
Significantly higher arrest rates (more frequently for aggressive offenses, more frequently charged, and convicted) and a propensity toward recidivism;
Higher rates of smoking in children with ADHD (boys have a two-fold increased risk for smoking and a two-year earlier onset for contemplating smoking);
Adults smokers with ADHD are a difficult group to wean from nicotine addiction (there are current studies working with adults with ADHD and a nicotine antidote).
Impulsivity and poor decision-making may contribute to susceptibility or attraction to substance use but it may be more dependent on the comorbid conditions than on ADHD. However, it should be noted that medication does not enhance or increase drug use among ADHD children. In fact, unmedicated ADHD children have the highest substance abuse rate.
Q2. How strong of a risk factor is childhood ADHD for the development of later psychiatric comorbidity or secondary conditions such as childhood disruptive disorder and adult antisocial disorders? (Consider by what mechanism ADHD predisposes one to later psychopathology and to what extent ADHD is a reliable marker for its development?)
The Developmental Decay Theory posits that ADHD may be the antecedent of disruptive behavior disorder and ultimately ASPD rather than a single, distinct disorder. Potential for the development of other conditions is quite high.
Early development of CD almost requires that ADHD be present in early youth; however, adolescent onset of CD does not appear to have the same developmental trajectory.
Data show the combined subtype as having more comorbidity and poorer long-term outcomes; however, more research of the inattentive subtype may find this group highly comorbid, too, but with more cognitive dysfunction rather than behavioral non-conformity.
ADHD youth start smoking and using illicit substances earlier than their normal peers.
ADHD youth with learning disabilities have particularly negative educational paths and those with comorbid disorders or high levels of impulsivity have additional socialization impediments.
Maternal smoking during pregnancy is potentially a significant risk factor for the development of ADHD and other psychopathology in offspring.
The Isle of Wight study in Great Britain identified several risk factors associated with the mental health of children, including low social class, parental discord, family conflict, maternal-natal health, and paternality. These environmental factors may also contribute to the expression of comorbidity in ADHD.
Q3. Discuss the role of ADHD in the propensity to participate in health risk behaviors. Do we know, given ADHD, what are the risk factors or pathways leading to participation in risky behaviors?
There are three predictors of ADHD persistence and continued impairment: family history, comorbidity, and adversity. The more predictors there are, the more the likelihood of persistence. Impulsivity is one of the most significant predictors of poor outcomes in ADHD and contributes to health risks in youth.
Adversity itself is not a risk factor, but it is involved in fueling and maintaining the disorder. Studies in monkeys have shown that even minor stress impairs prefrontal cortex function and this finding could shed light on potential population differences and risks.
The disorder is characterized by impulsivity and irrational decision-making and these core characteristics are likely to cause accidents of all kinds. Adolescents with ADHD are particularly at risk on the roadway.
ADHD is not a condition associated with low fertility and the risk for many ADHD teens to impregnate or be impregnated by other teens is high. Sexual activity among ADHD persons is one area of potential risk in which little work has been done.
Increased rates of smoking in children with ADHD may be related to attempts to self medicate: smoking activates the nicotine receptors releasing dopamine, the deficit of which is thought to drive ADHD impairments.
The most difficult adult group to wean from smoking is adults with ADHD. Research efforts are currently underway that will work with ADHD adults and a nicotine antidote.
Q4. Is there basic descriptive epidemiology on ADHD and these conditions? (Consider how they vary by race, gender, age, SES, and which comorbid conditions or behaviors persist throughout the lifespan)
ADHD is a disorder with many etiologies and, even though the phenotype is narrowly defined, there are genetic origins and environmental factors that, as yet, we do not have a handle on.
Population-based studies are lacking in American research of ADHD, but the finding that ADHD must be present in early childhood for the development of early CD comes from a British study that was population-based.
Literature and research of ADHD in minority populations is almost non-existent.
Research in other countries and a few American studies suggest that SES might be related to the prevalence of ADHD, if it is related to disadvantage.
Q5. Are comorbid conditions being appropriately diagnosed and treated in individuals with ADHD?
The sentiment of the experts present at the meeting was that comorbidity is not being properly diagnosed and often goes untreated.
There is little diagnostic precision for comorbid psychiatric conditions and general practitioners often associate depression and anxiety with the vicissitudes of life, even in those patients without ADHD, and consequently, they go unrecognized as comorbid conditions.
The focus of treatment for those individuals who present with significant behavioral comorbidity is placed on the antisocial behavior, rather than on the ADHD, which is often ignored. This may be especially pertinent when considering ADHD youth in the juvenile correction setting.
Additionally, there is a wider circle of children with incomplete syndromes (ADHD), not otherwise specified, who are missing from ADHD diagnoses and whose impairments may not be identified or treated appropriately.
Q6. Are there effective interventions for comorbidity or the prevention of secondary conditions in those with ADHD? (Consider for which conditions and/or associated health risk behaviors)
Although there was no evidence to date that either ADHD or CD could be prevented, that does not mean that attempts to develop prevention strategies should not occur.
It was noted that we may find that we are able to address juvenile violence with treatment, a possibility which may change the course of some comorbidity, such as substance abuse and other psychopathology.
Current interventions for many of the comorbid disorders consist of psycho-pharmacological therapies and have some success, but the benefits of combination therapies (medication and other therapies) should be considered, depending on the child's symptoms.
This is an area that needs more research and consideration.
Q7. Do current available interventions appreciably alter long-term outcomes for these individuals?
Research to date has not addressed this question in terms of school performance, interpersonal relationships, and job functioning/underachievement among ADHD adults. ADHD adults do have difficulty in these domains, but it is not known if current treatments in childhood relate to more positive outcomes in such areas of adult functioning.
There do not appear to be significant differences in the rate of employment of persons with ADHD and those who do not have the disorder, although those with ADHD have lower levels of employment, and their job performance is usually impaired.
Q8. To what extent do comorbid conditions and health risk behaviors pose a burden on society? (Consider effects and costs on social systems, family, school, juvenile justice system, workforce, risk of substance abuse, and injury throughout the lifespan)
ADHD also has a large impact on the juvenile justice system and on adult jails. Persons with ADHD are impulsive, and this impulsive behavior relates to their risk for irrational actions that may result in incarceration.
Resources need to be targeted toward those with comorbid conditions since these individuals have the worst outcomes and pose the largest amount of burden to our social systems.
The health risk behaviors associated with ADHD pose social burden in a particularly dangerous way. Driving accidents among ADHD adolescents and adults are a public health concern and one that CDC may have a prevention role in.
Little research has attempted to quantify the cost of ADHD along much less comorbid cases in terms of disruption to families, employment loss, and the cost of under-achievement.
Cost to social systems such as education, juvenile justice, and medical services would not be difficult to ascertain and CDC may have the skills to provide this information where it is currently unavailable or lacking.
Q9. What is the current state of Public Health research in this area? What are the gaps in your opinion and what can CDC do?
CDC is uniquely situated to advance the study of the health economic impact of ADHD, and to conduct a financial assessment of what the condition is costing society.
CDC could develop driver education programs for ADHD teens, for parents, and for schools.
CDC could develop a 10-minute screening tool that would help physicians (similar to screeners such as the Child Behavior Checklist, the ADHD Attention Scale, and the Conduct Disorder Delinquency Scale) to identify potential cases of ADHD and comorbid conditions early and routinely.
The first step in the public health method is to identify the problem. CDC could lead efforts to find an easy, reasonable, and reliable way to identify ADHD and comorbidity.
CDC could develop information packages or other health communication materials for the parents of ADHD children.
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