Why Are ADHD Rates So Much Higher in the U.S.?

Chances are, you know someone with attention deficit hyperactivity disorder (ADHD), or you might have it yourself.

ADHD is a complex condition characterized by symptoms like a constant inability to pay attention, impulsiveness, trouble sleeping, and mood swings. According to the latest data from Centers for Disease Control and Prevention, an estimated 7 million children in the U.S. (11.4% of all children) have been diagnosed with ADHD, along with 15.5 million U.S. adults (6% of the adult population)—half of whom were diagnosed as kids.

These numbers aren’t fixed, however. The prevalence of diagnosed ADHD has steadily risen in the U.S. over time, and can differ significantly from state to state. Globally, ADHD rates tend to be lower than those seen in the U.S., though prevalence has been increasing in some parts of the world. The reasons for this increase in diagnosed ADHD, or the differing rates across states or countries, aren’t clear.

It’s possible that much of this increase simply reflects doctors becoming better at recognizing ADHD in children and adults over time. But ADHD is also predominantly thought to be caused by a complicated mix of genetic and environmental factors, and it’s possible that some of these factors might be on the rise. In perhaps the weakest version of that theory, Robert F. Kennedy Jr., the Secretary of Health and Human Services, appeared to imply recently—without any supporting evidence—that the rise in ADHD and other neurological conditions is being caused by food dyes or another supposed environmental toxin.

Some researchers have argued that at least part of the difference in ADHD rates can be attributed to cultural perceptions of the behaviors associated with it—particularly in children—as well as other societal factors.

For this Giz Asks, we reached out to psychologists, psychiatrists, and medical historians to get their take on why ADHD rates vary so widely from place to place. The following responses may have been lightly edited for clarity and grammar.

Kevin Antshel

A psychologist specializing in ADHD and other developmental conditions at Syracuse University.

The prevalence of ADHD in children varies between 5% and 10% depending on the region of the world. ADHD prevalence rates are generally higher in the U.S. (closer to 10%) and lower in Europe and Asia (closer to 5%). Rather than biology, there are medical, social/cultural and educational explanations as to why ADHD is more common in the U.S.

Medical: Children in the U.S. are more often screened for ADHD by primary care physicians than in some other places in the world. In addition, the Diagnostic and Statistical Manual of Mental Disorders (DSM) is used to diagnose ADHD in the U.S. and has a wider diagnostic criteria for ADHD than the International Classification of Diseases (ICD) which is used in most other parts of the world. Finally, the U.S. is one of only two countries (New Zealand is the other) which allows direct-to-consumer advertising of medications. This increased awareness of treatment options likely contributes to higher diagnosis (and medication rates). All three of these medical explanations sets the stage for ADHD to be more often diagnosed in the U.S.

Social/Cultural: In the U.S., ADHD is widely known and discussed. This increased awareness can lead to caregivers and teachers noticing inattentive and/or hyperactive- impulsive symptoms more frequently. These behaviors might then be quickly labeled as “disordered” rather than considered as within the range of typical child development. In comparison to other places in the world (especially Asia), there is somewhat lower stigma regarding ADHD in the U.S. The relatively lower level of stigma can lead to more caregivers seeking and accepting ADHD treatment. Finally, K-12 U.S. schools often emphasize self-control in the classroom (e.g., stay seated for 6+ hours per day). This emphasis on self-control may make ADHD-like behaviors more noticeable in school. All three of these social/cultural explanations sets the stage for ADHD to be more often diagnosed in the U.S.

Educational: In the U.S., an ADHD diagnosis can lead to the provision of school services, resources, and accommodations. This can lead to an inherent incentive to diagnose the condition. In my opinion, this is likely the greatest single influence on the higher ADHD prevalence rates that are commonly reported in the U.S.

Matthew Smith

Professor of health history at the University of Strathclyde’s Center for the Social History of Health and Healthcare and author of the 2011 book Hyperactive: The Controversial History of ADHD.

One of the reasons ADHD is most commonly diagnosed in the United States is that it is where it was first diagnosed. Whereas most countries began diagnosing ADHD in the 1980s and more often in the 1990s, American children were first diagnosed with what we’d recognize as ADHD in the late 1950s. That is when the term Hyperkinetic Impulse Disorder was coined. Previously, hyperactive, impulsive children were only thought to be problematic when their behaviors were very severe or associated with underlying brain damage. Of more concern to child experts were shy, inactive, withdrawn, and nervous children. In contrast, Hyperkinetic Impulse Disorder, coined in 1957, was depicted as common, occurring in most classrooms.

Following the Soviet launch of Sputnik (also in 1957), Americans grew concerned about why they appeared to be lagging behind in the Space Race. The National Defense Education Act was passed in the next year, placing more focus on core subjects, encouraging students to stay in school or college for longer, and hiring guidance counsellors to identify under-achievers. Those singled out as not meeting expectations were often diagnosed with Hyperkinetic Impulse Disorder.

At the same time, the manufacturer of the drug Ritalin was looking for a market. It was approved to treat hyperactive children in 1961, spurring an aggressive marketing campaign that promoted not only the drug, but the disorder it was meant to treat. While some of the tactics employed by drug companies were restricted in the 1970s, the advent of direct-to-consumer advertising in the 1980s and 1990s boosted the popularity of the disorder, now called ADHD, even further.

Alongside these factors, we also have to consider the environmental factors thought to contribute to ADHD behaviors, ranging from synthetic food additives and exposure to atmospheric lead, to lack of exercise and time in nature. Many of these contributing factors have been and continue to be more significant in the U.S. than in other countries.

Joel Nigg

Professor of psychiatry and co-director of the Center for Mental Health Innovation at Oregon Health & Science University’s School of Medicine.

The usual scientific opening and the boring answer: a combination of multiple secular [long-term, non-cyclical] factors. But we can name some of them.

First, laws are different. For example, in the U.S., educational laws mean that a diagnosis of ADHD can enable resources to be marshaled for children struggling in school—thus it really matters if a child has a diagnosis of ADHD and when they struggle in school, this gets looked at much more quickly than in other countries.

Second, treatment guidelines are different across countries. In some countries, medication is only rarely prescribed to children, but guidelines in other countries, including the U.S., encourage use of medication as a first line treatment due to its low cost, general efficacy, and limited availability of other options.

Third, the quality of the health care system matters. The U.S. system is patchy at best, and so it is often not possible for a child to get the support they need—what appears as ADHD may be better seen as another issue, but the resources to identify and support other issues are insufficient, and ADHD becomes the “low hanging fruit” to address.

Fourth, clinician ideas of how to diagnose ADHD, and at what threshold to do so, vary widely. Even within a single state in the U.S., we have seen that rates of identification of ADHD vary markedly from one county to another. The best studies I have seen indicate that cross-national differences in true prevalence (as distinct from case identification) are small (ranging from 2% to 4% or so), whereas case identification rates vary much more widely.

Although genetic influences are extremely important in ADHD, environmental exposures also matter to etiology. (We have not seen any evidence so far that population genetic variation is sufficient to affect prevalence). Thus, although not well demonstrated, it is likely that regional differences in relevant risk factors (for example, air pollution, ambient lead exposure, poverty and resource availability for families, maternal health during gestation and perinatal health, rates of family trauma) also account for within-country regional variation, as well as partly influencing cross-national variation in both true prevalence and case identification of ADHD or ADHD-like problems.

Stephen Hinshaw

Distinguished professor of psychology at the University of California, Berkeley and director of the Berkeley Girls with ADHD Longitudinal Study, the longest follow-up study of its kind.

ADHD is the latest name for a constellation of problems and impairments that have been professionally recognized since the advent of compulsory education. It’s controversial—particularly because, just as is the case with other mental and neurodevelopmental conditions there is no objective biological “marker” (as there is for coronary artery disease or cancer) to pinpoint its presence. Nonetheless, an individual with levels of attention dysregulation, impulse control problems, and difficulty organizing one’s life may well display, over time, impairments in academic performance, social interactions, job performance, and regulation of emotions.

And for those who might think that ADHD is a convenient label for lax parenting or difficult schools, there is a ton of evidence that the later-life issues they experience too often include low self-image, either aggressive or depressive behaviors, high risk for accidental injuries, and especially for girls, high rates of unplanned pregnancies, exposure to intimate partner violence, and self-inflicted injury (including both non-suicidal self injury and actual suicidal behavior).

Why some people have high levels of ADHD but most do not is related far more to genetic differences across individuals than to differences in family interactions or contexts. Thus, ADHD (via twin and adoption studies) is significantly heritable. Still, even if one has the genetic predisposition (spanning many genes, each operating to produce a small amount of risk), how one is parented and schooled can go a long way toward exacerbating or instead minimizing impact via building of strengths.

International studies over the past 17 years have found, intriguingly, that in countries with compulsory education, the rates of diagnosed ADHD in children and teens are remarkably consistent—comprising around 5 to 8% of the population of young people. This provides circumstantial evidence for the proposition that when youth with genetic propensities for an exploratory, impulsive style are made to go to compulsory education, a remarkably similar percentage have real difficulties with self-control.

However, two countries with rates of diagnosed prevalence well above these international rates are the U.S. and Israel—both of which have extreme levels of academic pressure to succeed. In fact, in a book I co-authored with the health economist Richard Scheffler, The ADHD Explosion, we found that the underlying major differences in ADHD diagnostic rates across U.S. states could be pinned to state-by-state differences in educational policies related to district-wide standardized test scores. That is, in states that suddenly mandated certain levels of academic performance in order to maintain state support for those districts, rates of ADHD diagnoses rose precipitously over the ensuing years—because of pressure to get such youth treated and because of policies at the time that excluded youth diagnosed with ADHD from being counted in the district’s test-score average (because these were now “special ed” kids).

Overall, despite the psychobiological reality of ADHD, when carefully assessed, it may well be that social and cultural pressures to “perform” can falsely inflate rates of diagnosis (a) when there is pressure on public schools to produce better test scores at all costs and (b) given the tendencies for many non-specialist professionals to yield a quick diagnosis in absence of the needed time and effort to make a valid diagnosis.

Finally, though you didn’t ask, there’s been a 100-year-long ignoring and discounting of the possibility that girls and women can “have” ADHD. A lot of work in my lab has shown this to be a myth: Boys ARE about twice as likely as girls to develop ADHD, but this is wildly different from the supposed 10:1 difference so often posited. Girls tend to show a less ornery and overt form of ADHD than boys—and professionals must catch up with the latest diagnostic standards.