Adult ADHD is ADHD that has been identified in adulthood versus childhood. Most often, ADHD symptoms manifest in early childhood, and become apparent to parents, teachers, or pediatricians during routine check-ups. Sometimes, ADHD symptoms will not be identified even if they are present. This occurs for a variety of reasons. At times, there are stressors within the family system or mood symptoms present (e.g., depression) that can “mask” the presence of ADHD symptoms. At other times, very intelligent children who are hardworking can “push through” their inattention and do well in school, even though they may have ADHD symptoms that cause them to work harder than other kids without the diagnosis. Also, when children have a primary inattentive type of ADHD with no hyperactive-impulsive symptoms, inattention may not be noticed as readily because overt disruptive behaviors are not present. Whatever the case may be, these “missed” childhood cases can become problematic in adulthood because an individual is struggling to focus within the workplace, or perhaps is struggling within the home environment because of poor organization and planning. When these adult cases are identified in adulthood, they are called “adult ADHD.” Finally, in rare cases and for unknown reasons, symptoms of ADHD may begin to manifest in adulthood when they were not present in the person’s childhood. These cases may result from head trauma, medical conditions, environmental toxin exposure, or age-related cognitive decline. Regardless of the origin, these manifestations of ADHD are referred to as “Adult-onset ADHD.”