The ADHD challenge
The core symptoms of ADHD frequently cause significant impairment in academic, social and behavioral functioning that adversely impact individuals’ quality of life. These symptoms often persist into adulthood, potentially compromising an individual’s functioning over many years. Understanding how ADHD impacts long-term functioning, and whether adverse long-term affects are diminished with treatment, is thus extremely important. However, despite ample evidence that treatments such as medication and behavior therapy yield substantial short-term benefits for most individuals, the impact of treatment on longer-term outcomes remains less well-established. This is an important gap in the research literature.
In last month’s issue of Attention Research Update I reviewed a paper that synthesized research on long-term academic outcomes for youth with ADHD. Key findings were that academic outcomes were generally better for treated vs. untreated youth, but generally remained significantly below outcomes attained by youth without ADHD.
What about the impact of ADHD and ADHD treatment on long-term outcomes in other important domains such as social and occupational functioning, antisocial behavior and substance use, driving, and self-esteem? Is there evidence that treatment helps? Does it help enough to normalize outcomes relative to those without ADHD?
The evidence review
These important issues were addressed in a paper titled ‘A systematic review and analysis of long-term outcomes in attention deficit hyperactivity disorder: Effects of treatment and non-treatment’. The paper was published in 2012 in BMC Medicine.
The authors began by searching for relevant studies published between 1980 and 2010. All studies compared outcomes in participants with and without ADHD or between treated and untreated participants with ADHD. A total of 351 studies were identified; these included longitudinal studies where individuals were followed for at least 2 years and cross-sectional studies where outcomes were measured in groups of participants at different ages. Only studies where outcomes were assessed in individuals at least 10-years old were included. The ages of participants in these studies extended from children to older adults.
It is important to note that the studies included were quite varied and have different methodological strengths and weaknesses. And, many were not ‘long-term’ in the sense of following individuals diagnosed in childhood to learn how they were doing as young adults; instead, the authors chose to define ‘long-term’ as 2 years or more. These issues are problematic, but being more restrictive on the studies included would have introduce different challenges, e.g., too few studies to analyze. Thus, limitations in what can be concluded from the authors work are inevitable and reflect limitations in the studies they had to draw on.
As noted above, 351 studies were included for analysis. Many of these studies included more than one outcome, so the number of outcomes compared exceeded this total. Nine different types of outcomes were examined. These outcomes, and the number of studies in which each was examined, are as follows:
- Drug use/addictive behavior — 160 studies
- Academic outcomes — 119 studies
- Antisocial behavior — 104 studies
- Social functioning — 98 studies
- Occupational functioning — 45 studies
- Self-esteem — 44 studies
- Driving outcomes — 30 studies
- Service use (emergency health care, financial assistance) — 26 studies
- Obesity — 10 studies
Across all studies, the average length of time for which researchers collected data on participants was 9 years; the range of time for which data was collected was 2 years to 40 years. As noted above, the studies included participants across a wide age-range.
Comparing results across such disparate studies is complicated, particularly given the variety of outcomes examined and the measures used to examine them. This makes it challenging to combine results across studies into a single analysis, as is frequently done in meta-analytic work. As an alternative, the authors counted how often outcomes were significantly different between the groups compared in each study, e.g., youth with and without ADHD or treated vs. untreated youth with ADHD. They then counted the number of times that outcomes were found to be significantly different.
For example, if driving outcomes were compared between treated vs. untreated individuals with ADHD in 22 studies, they counted how many times the outcome was significantly better for treated individuals and how many times there was no significant difference.
Outcomes comparing individuals with untreated ADHD to peers
A total of 333 studies compared outcomes between untreated participants with ADHD and controls; in many of these studies, multiple outcomes were compared. Overall, outcomes for individuals with untreated ADHD were significantly worse than for comparison subjects approximately 75% of the time. Information on whether this varied significantly across different outcomes, and how much worse outcomes for untreated participants tended to be, was not provided. Thus, one can’t conclude much from this summary beyond the fact that individuals with untreated ADHD tend to fare worse over the long-term in multiple domains relative to those without ADHD.
Outcomes with ADHD treatment
Treated vs. untreated ADHD was compared in 48 studies involving 76 outcomes. For 72% of the outcomes, treated individuals were doing significantly better. For the remaining 28% of outcomes, treated and untreated individuals generally did not differ although in rare instances treated individuals were doing worse.
The likelihood that treatment was linked was linked to better outcome varied considerably across the different outcomes examined. Treated individuals did better than untreated individuals for 100% of driving and obesity outcomes, 90% of self-esteem outcomes, 83% of social functioning outcomes, 71% of academic outcomes, 67% of drug use outcomes, 50% of antisocial behavior outcomes, 50% of service use outcomes, and 33% of occupational outcomes.
Thus, for all outcomes except for antisocial behavior, service use, and occupational functioning, treated individuals were likely to be doing better. For the latter 3 outcomes, however, treated individuals were doing better between one-third and one-half of the time, and about the same the rest of the time.
It is important to note that treatment varied across studies and determining the quality of treatment received was not possible. In most studies, participants received medication treatment; however, non-medical treatment and treatment that combined medication with other treatments were also common. Treatment type did not seem to be associated with the likelihood of better outcomes but details on this were not provided.
Does treatment normalize outcomes?
The results above suggest that ADHD treatment is generally associated with better outcomes. However, is treatment likely to normalize outcomes relative to individuals without ADHD?
This was examined in 42 studies that included 76 different outcomes. In most cases, outcomes were not normalized with treatment, meaning that individuals with ADHD were doing significantly worse than comparison subjects. This was found for 58 of the 76 outcomes examined. Thus, equivalent outcomes between treated participants and controls were found only 18 times.
An important caution
The above results suggest that treatment generally provides long-term benefits to individuals with ADHD but that it does not typically ‘normalize’their outcomes. Because the studies considered by the authors included ones from both North America (US + Canada) and Europe, the authors also examined whether treatment outcomes varied geographically. It appears that they did.
Specifically, 86% of outcomes for studies conducted in Europe were consistent with treatment benefits compared to only 50% of outcomes for North American studies. This may be because North American studies tended to use prospective designs in which individuals with ADHD who did vs. did not receive treatment were followed over time while European studies were typically retrospective studies of adults. The former would generally be considered a stronger design so one possible interpretation is that more rigorous studies were less likely to document long-term benefits of ADHD treatment.
Summary and implications
The authors’ ambitious goal in this paper was to summary existing research on long-term outcomes associated with ADHD to address 3 fundamental questions:
- Without treatment, how often do individuals with ADHD experience significantly worse outcomes than those without the disorder?
- Is there evidence that ADHD treatment improves long-term outcomes? And,
- Is there evidence that ADHD treatment generally normalizes outcomes?
To address these questions, they identified over 350 studies conducted in North America and Europe in which diverse outcomes were examined over at least a 2‑year period. A wide mix of studies and ages were included, and detailed information on the type, duration, and quality of ADHD treatment was not provided (although this may be examined in subsequent work). While this makes it difficult if not impossible to draw firm conclusions, the pattern of results obtained converge on the following:
- Without treatment, the majority of individuals with ADHD attain significantly poorer outcomes in multiple domains relative to peers.
- Treatment generally results in more positive outcomes relative to no treatment, particularly for driving, obesity, self-esteem, and social functioning. The consistently positive results found for obesity may reflect the appetite suppressing effects of stimulant medication. Antisocial behavior and occupational outcomes were less likely to show benefits with treatment.
- Although ADHD treatment generally results in better long-term outcomes relative to no treatment, even with treatment outcomes are typically not normalized. Thus, most individuals with ADHD continue to be doing less well in multiple domains than their peers.
As noted above, limitations in the research base that the authors had to drawn on limits any conclusions that can be made about the long-term impact of ADHD treatment. In addition, the authors did not consider how different types of treatment or duration of treatment effected treatment outcomes, although they indicate plans to do this in subsequent work. They also did not discuss the magnitude of treatment effects, which makes it difficult to know how often statistically significant differences between treated and untreated individuals were likely to be clinically meaningful.
Thus, despite the significant effort represented by this paper, important questions remain about the long-term impact of ADHD treatment. In fact, the authors conclude their paper by stating that the “…question remains as to whether the short-term benefits demonstrated by short-term drug or non-pharmacological treatment studies translate into long-term outcomes.”
Hopefully, subsequent work by these authors and others in the field will soon provide a more definitive answer to this basic and important question.
– Dr. David Rabiner is a child clinical psychologist and Director of Undergraduate Studies in the Department of Psychology and Neuroscience at Duke University. He publishes Attention Research Update, an online newsletter that helps parents, professionals, and educators keep up with the latest research on ADHD, and teaches the online course How to Navigate Conventional and Complementary ADHD Treatments for Healthy Brain Development.