It has been said that "ADHD rarely travels alone." This refers to the high incident rate of having ADHD and at least one other psychiatric disorder. Some experts put this as high as 90 percent of individuals, although a more accepted estimate would be anywhere from 40 percent to 65 percent of those with ADHD will also be diagnosed with a second disorder at some point.

The following table shows the most common comorbid conditions and their rate of prevalence in the ADHD community, according to Psychiatric Times [1]:

When children are diagnosed with ADHD, the most recommended form of treatment is a combination of behavioral strategies and medication. Often, however, when other conditions are present, this treatment doesn't always bring about the results parents are looking for. In addition, the presence of related conditions in children with ADHD can signal a higher likelihood that symptoms will continue to cause impairment into adulthood.

Complications in Diagnosis

Which came first, the chicken or the egg? Often, doctors are faced with a similar dilemma when diagnosing a child with multiple disorders. For example, when a child with ADHD also has depression, is the depression a result of frustrations, academic struggles and poor social skills brought on by symptoms of ADHD or is the depression a separate diagnosis? If depression is a result of ADHD symptoms, then by treating ADHD, the depression symptoms may work themselves out and additional medication and treatment may not be necessary. If, however, the child suffers from both ADHD and a major depressive disorder, treatment of both will be needed.

Although each psychiatric disorder has its own set of unique symptoms, many times these will overlap. For example, a child with anxiety disorder may find it difficult to concentrate and anxious feelings may show up as being unable to sit still, restlessness, or hyperactivity.  This can create problems during the diagnostic process.

Many times, as one condition is treated, the symptoms of another appear. For example, a child with bipolar disorder and ADHD may first be diagnosed with ADHD. As treatment begins to reduce symptoms of inattention or impulsiveness, other symptoms, such as manic episodes or depression may be more apparent. Although both conditions were present in the beginning, some symptoms may have been masked, hidden or mistakenly attributed to the ADHD. It is only after the ADHD was controlled that the symptoms of bipolar could be seen.