Researchers may classify ADHD as a neurological, psychological, or psychiatric condition. They may also classify the condition as a developmental disorder.

ADHD affects the development of the brain, causing a person to display certain behaviors and psychological states that do not generally present in neurotypical people.

Some sources classify ADHD as a neurological disorder on the basis that it affects neurodevelopment. Others characterize it differently — for example, as a psychiatric disorder or a neurobehavioral disorder.

Historically, doctors used the term psychological to refer to conditions involving specific mental states, such as emotions, thoughts, and behaviors, which present through human interactions. Neurological was the term for medical conditions that have a more clear-cut origin in the brain. Finally, psychiatric conditions were those that originated in the brain but had no obvious biological explanation.

Researchers increasingly assert that this distinction is meaningless. Neurological conditions can have behavioral or emotional components, while psychological conditions can affect the body. Thus, ADHD is a neurological, psychological, and psychiatric condition.

Regardless of how researchers classify ADHD, they tend to emphasize its neurological roots, including the way it changes brain chemistry. ADHD is, therefore, also a developmental disorder.

Keep reading to learn more about defining ADHD as a neurological condition, as well as the differences between neurological, psychological, and psychiatric conditions.

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Researchers have identified several ways in which the brains of people with ADHD differ from those of people without the condition. These differences relate to:

  • Brain volume: People with ADHD have slightly lower brain volumes than neurotypical people. A 2017 study found that these volume differences affected several areas of the brain, including the accumbens nucleus, caudate nucleus, hippocampus, amygdala, putamen, and amygdala. The differences were most significant among children.
  • Brain composition: ADHD changes the behavior of gray matter and white matter in the brain and reduces the volume of gray matter. It may also change the behavior and structure of the prefrontal, occipital, and parietal lobes. Gray matter is where most neuroprocessing occurs, while white matter communicates these processes to the rest of the body.
  • Neural networks: Brain signals travel through the brain in networks. ADHD has a link with changes in these networks that may affect functioning. In a 2021 study, people with ADHD had changes in neural networks in their gray and white matter. These changes correlated with deficits in working memory and attention.
  • Neurotransmitters: Neurotransmitters are chemicals that carry signals across a nerve synapse. People with ADHD have different levels of several neurotransmitters, including norepinephrine and dopamine. Dopamine plays a key role in pleasure, motivation, and reward, and ADHD drugs often act on this neurotransmitter.

Although several studies provide evidence of brain differences between people with ADHD and neurotypical people, these brain differences are not consistent and vary from person to person. In addition, it is not possible to generalize the results from large studies to an individual person.

As experience can change the brain, it is difficult to know whether:

  • these brain differences cause ADHD
  • ADHD causes these brain differences
  • the experiences of people with ADHD alter the behavior of their brain

Furthermore, other medical and psychiatric conditions — such as diabetes and substance use disorders — may also affect the brain. Due to this, it remains unclear whether these subtle brain differences are due to ADHD or something else.

Learn more about brain differences in people with ADHD.

Several other neurological disorders affect the development of the brain, altering behavior and brain function early in life. They include:

  • autism spectrum disorder, which affects mental health, social relationships, and communication
  • cerebral palsy
  • intellectual disability, which affects the ability to learn across many domains
  • learning disabilities, which affect specific domains of learning, such as reading
  • conduct disorder, which causes problematic or aggressive behavior
  • hearing and vision impairments, which alter or eliminate the ability to hear or see

People with ADHD often have other neurodevelopmental disorders. A 2020 study of 336 adults with a new diagnosis of ADHD or autism found that 72.8% had at least one other mental health condition.

According to the Centers for Disease Control and Prevention (CDC), 14% of children with ADHD have autism, and 1% have Tourette’s syndrome. Psychological diagnoses are even more common, with 52% having a behavioral or conduct issue, 33% experiencing anxiety, and 17% having depression.

A 2020 article paper emphasizes that there is no clear line between neurodevelopmental disorders and other psychiatric conditions. The paper reports that bipolar disorder and schizophrenia share a genetic link to neurodevelopmental disorders and may exist on a continuum with them.

This continuum suggests that neurodevelopmental disorders share some common genetic origins and that various developmental processes may result in different neurodevelopmental disorders. The overlapping genetics of these diagnoses may help explain why they often occur together.

The difference between neurological and psychological conditions is not clear, as a continuum of disorders affects the brain and behavior. Conditions that most doctors consider neurological, such as Parkinson’s disease, can also affect psychological states and behavior.

Similarly, psychological conditions can affect the body, such as when depression causes physical pain or autistic people develop tics.

Some researchers now argue that the line between neurology and psychology is arbitrary and not based on real differences between the two groups of conditions.

Even for those who accept the difference, though, ADHD has both psychological and neurological characteristics. It correlates with specific differences in brain structure and chemistry but also changes psychological states, causing impulsive, hyperactive, and inattentive behaviors.

However, because it is typically psychologists and psychiatrists who treat the symptoms of ADHD, most people view it as a psychological or psychiatric condition.

ADHD is a neurodevelopmental condition, which means that it affects a person’s development, altering their psychology and their behavior. Adults and children with ADHD display differences in their brains compared with people with typical development.

They are also more likely to have other neurodevelopmental disorders. This fact points to a neurological origin for ADHD. However, as the distinction between neurological and psychological conditions is murky, and the science may not support it, it is possible to classify ADHD as a neurological condition, a psychological disorder, or both.

People seeking treatment for ADHD typically seek support from a psychologist, psychiatrist, or therapist rather than a neurologist. Neurologists typically treat conditions such as Parkinson’s disease and brain injuries, not psychological disorders.