I have a family member who has ADHD.

The actual disorder of ADHD is the same in adults as it is with children. It is an inability to stay on task. This is not the same thing as being lazy. People who have ADHD are very motivated and want to be productive. They are easily distracted by any (and what feels like every) novel sensory input. A flash of light, a sudden flash of intuition, a strange noise, or someone walking past the person unexpectedly can shove their mind off task.

From WebMD

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Attention deficit hyperactivity disorder (ADHD) and attention deficit disorder (ADD) have symptoms that may begin in childhood and continue into adulthood. ADHD and ADD symptoms can cause problems at home, school, work, and in relationships.
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Most people don’t outgrow ADHD. An adult who’s ADHD is untreated (or inadequately treated) doesn’t usually have the hyperactivity. That symptom turns into restlessness. An adult with ADHD will continue to have problems finishing tasks and remembering to do tasks.

This inability to complete tasks can absolutely interfere with work. In addition, if a task is boring or mundane to a person with ADHD, he will be less likely to complete it. This can make landing and keeping a job very difficult.

ADHD in adults manifests differently than ADHD in children, as hyperactivity tends to decrease with age (for some but not all).

Although the exact prevalence in adults is unknown, studies thus far reveal that the condition probably exists in about 2 to 4 percent of adults, and is marked by the inability to maintain concentration, difficulty getting work done, procrastination, and organization problems.

A person’s inability to focus, sit still, concentrate, or follow instructions can greatly impair academic development or negatively affect their professional career.

Developing self-regulation is the biggest problem adults face when they have ADHD. This is often not expected of young children but is expected of adults. This self control affects an adult's ability not just to perform tasks, but to determine when they need to be done.

Individuals with ADHD have difficulty with certain brain activity, particularly in the area that is responsible for monitoring the behaviors that control planning and organization. This can be extremely frustrating to the ADHD adult.

When combined with ADHD, other learning disabilities can cause extreme frustration for adults or teens struggling at college or in the workplace. A few symptoms, such as disorganization, weak executive functioning, and inefficient use of strategies can be seen in ADD, ADHD, and other learning disabilities.

Although learning disabilities are common in adolescents with ADHD, they do not affect intelligence. People with ADHD span the same IQ range as the general population.

Attention Deficit and Hyperactivity Disorder (ADHD) is different for children and adults. For children, the symptoms of ADHD can begin to appear before seven years old. Boys are infected with this sickness in childhood. When the sickness is left undiagnosed and left without therapy, the child can bring this disorder until adulthood. People with ADHD cannot be reliable for work. They have to be brought to a different place such as exposure to nature for “green therapy.”

ADHD can be outgrown in adulthood provided that the treatment begins before this stage of development. Since this medical condition can begin before seven years old, it can be hard to determine if the child has ADHD. Children are naturally restless and hyperactive. Perhaps, ADHD is manifested when the child is unusually restless.