ADHD, or attention-deficit/hyperactivity disorder, is one of the most common mental health conditions among children in the U.S. And the diagnosis rate of this brain disorder—characterized by a difficulty focusing attention, restlessness, and impulsive behaviors—appears to have increased over the past 20 years, according to a new study published in JAMA.
The study is based on data collected by the National Center for Health Statistics at the Centers for Disease Control and Prevention (CDC) annually from 1997 to 2016. Researchers found that the prevalence of ADHD diagnoses in children and adolescents (ages 4 to 17) rose from 6.1 percent in 1997–1998 to 10.2 percent in 2015–2016. That's about a 67 percent increase. An increase was seen across the board, regardless of sex, race, ethnicity, family income, and geographic location, although it varied a bit among these subgroups.
This uptick in ADHD diagnoses isn’t exactly out of the blue, though. Previous research shows it’s part of a continuing trend. “It’s not just a sudden spike,” study coauthor Lane Strathearn, Ph.D., a developmental and behavioral pediatrics professor and director of the Division of Developmental and Behavioral Pediatrics at the University of Iowa’s Carver College of Medicine, tells SELF. “Over the past two decades, we’ve seen a gradual but progressive increase in the number of children diagnosed [with ADHD].” For example, the National Survey of Children’s Health found a 42 percent increase in diagnoses of 4- to 17-year-olds between 2003 and 2011.
So why are so many children reportedly diagnosed with ADHD today? Increased awareness of the disorder and access to medical care could be a factor.
“It may not be so much that ADHD itself has increased, but that the diagnosis of it has increased,” clinical psychologist Faye Dixon, Ph.D., clinic director at the UC Davis MIND Institute ADHD Clinic, tells SELF.
Experts point to a number of possible reasons for this increase, including an increase in health care access. The study authors credit the Affordable Care Act with potentially widening access to care, especially among minority and lower-income communities. “Kids who were being underserved medically before may now have access to resources they didn’t,” Dixon says, including things like ADHD screenings and referrals for clinical evaluations.
Researchers also believe we’ve simply become better at understanding the condition.
“Almost definitely, increased awareness and decreased stigma are major factors,” John Leikauf, M.D., a child and adolescent psychiatrist at Stanford Children’s Health, tells SELF. “There’s been greater public awareness—more good information out there that both parents and teachers are paying attention to,” Dixon adds. What’s more, doctors themselves are better trained to recognize symptoms and diagnose the condition than they were 20 years ago, Thomas J. Power, Ph.D., director of the Center for Management of ADHD at the Children's Hospital of Philadelphia, tells SELF.
In addition to a general increase in knowledge about ADHD, we’ve come to better understand how the condition manifests in girls in particular. The stereotypical presentation of a child with ADHD used to involve a hyperactive boy running around and disrupting class. And while boys are still diagnosed with ADHD more than twice as often as girls (14 percent of boys vs. 6.3 percent of girls, according to this recent study, the rate at which girls are diagnosed has doubled in the last 20 years from 3.1 percent to 6.3 percent (the rate in boys increased from 9 percent to 14 percent).
This disparity tracks with our increased understanding of ADHD in girls versus boys. “Professionals are more tuned in [now] to the way that ADHD manifests in girls,” Power says. While ADHD looks different in every child, boys classically demonstrate noticeable hyperactivity, while “girls often manifest their ADHD in less overt, more subtle ways,” Power says. “Their behavior tends to be less disruptive,” he explains, meaning they’re less likely to get the attention of a concerned teacher or parent than a boy who won’t sit still or stop talking. More often, he says, ADHD will negatively impact a girl’s learning and academic performance as opposed to her behavior in the classroom.
Some experts are worried that this study reflects an overdiagnosis of ADHD in the U.S.
Because there is no simple blood test or brain scan to detect ADHD, a proper diagnosis requires a comprehensive evaluation using a number of collaborative sources, Dixon says. This includes interviews with both the child and the parent (and potentially the teacher), symptom rating scales, observation by a doctor, and cognitive or academic assessments. “Performing a valid diagnostic appraisal takes real time,” Stephen P. Hinshaw, Ph.D., psychology professor at UC Berkeley, and psychiatry professor and vice chair the Department of Psychiatry at the UCSF Weill Institute for Neurosciences, tells SELF.
But it's possible that sometimes doctors may make a diagnosis too quickly or based on incomplete information, Power says. “Many non-specialists—pediatricians for kids [and] general practitioners for adults—are confronted with parents [and] individuals seeking an ADHD diagnosis,” Hinshaw says. “Within a 10 to 12 minute evaluation, and especially given the increased recognition of ADHD these days, it's quite possible that ADHD is a convenient diagnosis for individuals with a variety of conditions,” such as depression or anxiety.
It should also be noted that the data in this study could contain some "false positives" due to the way it was conducted, which relied solely on parent interviews rather than medical records or clinical evaluations, Dixon says. So some parents may have responded “yes” even if their child never got a formal diagnosis. “For instance, it’s not uncommon for physicians to say something like, ‘Your child may meet the diagnostic criteria for ADHD,’ or ‘We need to rule out a diagnosis of ADHD,’” Power says.
“The diagnostic rates that are reported here seem high to me,” Power tells SELF. “There’s no evidence to suggest that children are at greater risk of ADHD today… or that children are different biologically now with regard to the risk of ADHD. That doesn’t mean that’s not what happened, but we don’t have evidence yet.”
Other experts we spoke with, however, wonder if the incidence of ADHD is truly increasing. Strathearn tells SELF he's “a little bit weary about putting this increase just down to greater awareness or diagnosis." He tells SELF that increased awareness may only explain so much of the trend, which continues to rise even though ADHD has been in the mainstream conversation for years now. “We’ve been studying this for a while now,” he says. “I think we’ve reached the saturation point for that in terms of physician understanding and recognition of the problem. And even in the community—most people know about ADHD, they know friends who are on medication.”
If more kids are actually experiencing ADHD today than they were before, then the question becomes why that is.
What we know is that ADHD is caused by a mix of genetic and environmental factors and interactions between those things. “The best estimates we have right now indicate that most of the risk for ADHD is genetic, about 70 to 80 percent,” Dr. Leikauf says. (A review published in Molecular Psychiatry this year analyzed 37 twin studies and found a mean heritability of 74 percent.) The genetics are complicated, though, because each different gene contributes only a small amount of risk, Dr. Leikauf says. As Strathearn puts it, “There are markers that are associated with ADHD, but there’s no one marker that explains more than a small proportion of all the cases.”
Then there is the environmental component, which is even less well understood. “Only about 20 to 30 percent of the risk seems to come from the environment,” Dr. Leikauf says. Although genetics account for the majority of the risk, Strathearn points out that if we are seeing a true rise in ADHD, it seems likely that environmental factors play a role in the recent rise, “because genetics don’t change that quickly,” he says, i.e. over the course of 20 years.
There hasn’t been as much research into the environmental component as there has been into the genetic one, Strathearn says, although a number of lines of inquiry have been opened. The evidence we do have is not strong, because it’s difficult to single out any one factor as having a direct influence on a child's risk of developing ADHD.
There are several environmental risk factors that research has associated with an increased risk of developing ADHD, though nothing has been shown to be a definitive cause.
The environmental risk factor with the strongest evidence may be preterm birth and low birth weight. Hinshaw calls very low birth weight “a clear risk factor for ADHD.” A rigorous meta-analysis published in Pediatrics in 2017, which pooled data from 12 studies and 1,787 infants, found that babies born “very” and “extremely” preterm or at very and extremely low birth weights were about three times more likely to develop ADHD than children born full term at normal weight. (As Hinshaw points out, improvements in neonatal intensive care in the past couple decades means that more children born at extremely low birth weights are surviving.)
Other studies have suggested that exposure to toxins (like lead or smoking during pregnancy and traumatic brain injuries may play a role. It's also possible that some of these environmental factors may interact with genetics to increase a child’s risk, Hinshaw says. For example, “It may also be the case that increasing numbers of toxins in the environment—some of which interact with genetic risk for ADHD in certain cases—are leading to greater numbers of cases.”
One thing all ADHD experts can agree upon is that we need more research to figure out exactly what’s going on.
In light of data like this newest report, a clear understanding of ADHD may be more important than ever. We need to get better at figuring out why people develop ADHD and how to properly diagnose it while also making sure we’re not over- or mis-diagnosing it.
In addition to better diagnostic tools and more treatment options, learning more about the role of environmental factors could lead to possible preventions—especially for children who may be genetically predisposed to the condition.
”It’s very hard to change the genetics, but if there are environmental factors coming in play, that gives us the possibility to intervene and potentially prevent some of these developmental outcomes in the long term,” Strathearn says. “And in the long term, I think that gives us a lot of hope.”