Symptoms and causes

The primary features of attention-deficit/hyperactivity disorder include inattention and hyperactive-impulsive behavior. ADHD symptoms start before age 12, and in some children, they're noticeable as early as 3 years of age. ADHD symptoms can be mild, moderate or severe, and they may continue into adulthood.

ADHD occurs more often in males than in females, and behaviors can be different in boys and girls. For example, boys may be more hyperactive and girls may tend to be quietly inattentive.

There are three subtypes of ADHD:

  • Predominantly inattentive. The majority of symptoms fall under inattention.
  • Predominantly hyperactive-impulsive. The majority of symptoms are hyperactive and impulsive.
  • Combined. The most common type in the U.S., this is a mix of inattentive symptoms and hyperactive-impulsive symptoms.

While the exact cause of attention-deficit/hyperactivity disorder is not clear, research efforts continue. Factors that may be involved in the development of ADHD include:

  • Genetics. ADHD can run in families, and studies indicate that genes may play a role.
  • Environment. Certain environmental factors, such as lead exposure, may increase risk.
  • Development. Problems with the central nervous system at key moments in development may play a role.

Risk factors for attention-deficit/hyperactivity disorder may include:

  • Blood relatives, such as a parent or sibling, with ADHD or another mental health disorder
  • Exposure to environmental toxins — such as lead, found mainly in paint and pipes in older buildings
  • Maternal drug use, alcohol use or smoking during pregnancy
  • Premature birth

Although sugar is a popular suspect in causing hyperactivity, there's no reliable proof of this. Many issues in childhood can lead to difficulty sustaining attention, but that's not the same as ADHD.

Attention-deficit/hyperactivity disorder can make life difficult for children. Children with ADHD:

  • Often struggle in the classroom, which can lead to academic failure and judgment by other children and adults
  • Tend to have more accidents and injuries of all kinds than do children who don't have ADHD
  • Tend to have poor self-esteem
  • Are more likely to have trouble interacting with and being accepted by peers and adults
  • Are at increased risk of alcohol and drug abuse and other delinquent behavior