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About ADHD: Symptoms, Causes and Diagnosis

In this section:


What is ADHD?

Attention-deficit hyperactivity disorder (ADHD) is a condition characterized by inattention, hyperactivity and impulsivity. The most commonly diagnosed behavior disorder in young people, the Center for Disease Control and Prevention (CDC) reports that ADHD affects an estimated 9 percent of children aged 3-17 and 2-4 percent of adults.

Although ADHD has its onset and is usually diagnosed in childhood, it is not a disorder limited to children—ADHD often persists into adolescence and adulthood and is frequently not diagnosed until later years.


What are the symptoms of ADHD?

There are actually thought to be three different types of ADHD, each with different symptoms: predominantly inattentive, predominantly hyperactive/impulsive and combined.

Maureen DonaisMaureen E. Donais: My Story

My son started displaying symptoms at age three, but was not diagnosed with ADHD until second grade. That window of going without treatment led to a lot of frustration and guilt—my husband and I struggled with guilt because we did not know if our son’s behavior was due to our parenting style. Educating ourselves and the community was what really helped my family through these tough times.

As a member of NAMI Salem County, N.J., I was familiar with mental health issues. I had reached out to my local NAMI for assistance when I had custody of my niece who lived with mental illness. NAMI was my sounding board, it was a comfort zone, it was where I could vent about frustrations or fears and be myself. It was helpful to know that other families were going through similar circumstances. Together we needed to be hopeful and not dwell on the negatives—and that’s what NAMI does best.

The biggest challenge was getting my husband to understand that this was a medical problem, not a discipline problem. Through education, he came to understand and thus became very supportive, especially in terms of medication-based treatment. Once our son started medication, he was like a light bulb with an on and off switch—we now call his medicine his “good day” pill. Read more.

Those living with the predominantly inattentive type often:

  • fail to pay close attention to details or make careless mistakes in schoolwork, work or other activities;

  • have difficulty sustaining attention to tasks or leisure activities;
  • do not seem to listen when spoken to directly;

  • do not follow through on instructions and fail to finish schoolwork, chores or duties in the workplace;

  • have difficulty organizing tasks and activities;

  • avoid, dislike or are reluctant to engage in tasks that require sustained mental effort;

  • lose things necessary for tasks or activities;

  • are easily distracted by extraneous stimuli; and are forgetful in daily activities.

Those living with the predominantly hyperactive/impulsive type often:

  • fidget with their hands or feet or squirm in their seat;

  • leave their seat in situations in which remaining seated is expected;

  • move excessively or feel restless during situations in which such behavior is inappropriate;

  • have difficulty engaging in leisure activities quietly;

  • are "on the go" or act as if "driven by a motor;"

  • talk excessively;

  • blurt out answers before questions have been completed;

  • have difficulty awaiting their turn; and

  • interrupt or intrude on others.

Those living with the combined type, the most common type of ADHD, have a combination of the inattentive and hyperactive/impulsive symptoms.

It is also important to note that ADHD is a condition that often coexists with other conditions. Read more about ADHD and coexisting conditions.


While we don’t know for sure what causes ADHD, we do know that ADHD probably results from a combination of genetic and environmental factors. ADHD is a brain-based disorder and is strongly inherited, but parenting styles do not cause ADHD.

Genes are passed on to us from our parents and provide instruction for how our body develops and grows. Studies of twins prove that ADHD does run in families and more research is being done into what specific genes may make people more likely to develop ADHD. An NIMH research study showed that children with a certain gene have thinner brain tissue in the parts of the brain linked to attention. However, the research showed that this difference was not permanent and that as the children with this gene got older, the brain developed a normal level of thickness and their ADHD symptoms also got better.

Environmental factors found in our day-to-day lives can influence our health. Research studies have shown that there is a possible link between cigarette smoking and alcohol consumption during pregnancy and ADHD in children. Another study showed that preschoolers exposed to high levels of lead may have a higher risk of developing ADHD.


Diagnosing ADHD requires a comprehensive evaluation and cannot be done with one single test. A licensed health professional will compile information about the child’s academic, social and emotional functioning as well as rule out physical factors that could be causing symptoms similar to ADHD. Other factors such as anxiety, depression and some learning disorders may cause similar symptoms as ADHD and may coexist with ADHD.

Parents and teachers can provide an important history of the child’s behavior and when appropriate, as can the child. While the health professional will pay more attention to a child’s behavior in more structured settings, the child’s age must also be taken into account. It is important to note if the child’s behavior interferes with their day to day life and how often the behavior occurs. The Diagnostic and Statistical Manual IV is an important tool that needs to be included in the evaluation. In order to diagnose ADHD in adults, childhood history as well as current symptoms must be considered. For more information on diagnosis, visit NIMH and the National Resource Center on ADHD.