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 :
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.
Usually, the disorder that appears first is ADHD and therefore, it is frequently the first diagnosed.
The treatment of children with multiple diagnoses can be just as complicated as the diagnostic process. While medication and behavioral strategies together can improve symptoms of ADHD, this is often not the case when there is more than one diagnosis. It is important to determine whether there is a primary illness, one that is causing the majority of symptoms and the most impairment in a child's life. For example, Dr. Carol Watkins, in an article entitled, "AD/HD Co-Morbidity: What's Under the Tip of the Iceberg" discusses the presence of both ADHD and anxiety. She says "...the individual may be anxious because the AD/HD is making it difficult to succeed academically, vocationally or socially. If this is the case, treating the AD/HD may reduce the anxiety. If the anxiety is a separate entity, one must be more cautious about the use of stimulants because they can sometimes exacerbate anxiety. One may elect to treat the anxiety first, or treat the anxiety and the AD/HD at the same time. "
As you can see, adding a second, or third, diagnosis can complicate treatment. Doctors must take the time to evaluate each child, determining whether there is a "primary" diagnosis, which, when treated, will help to alleviate many of the symptoms or if each diagnosis is impairing function and must be treated as a separate illness.
In the case of separate diagnoses, the doctor must plan treatment accordingly. As Dr. Watkins indicates, some medications for ADHD can cause worsening of symptoms of other conditions, such as anxiety or bipolar disorder.
Although family doctors and pediatricians often treat children with ADHD, it may be more beneficial to consult a mental health professional for children with more than one condition.
"ADHD in Children with Comorbid Conditions: Diagnosis, Misdiagnosis, and Keeping Tabs on Both", 2007, May 3, Stephen V. Faraone, PhD., Arun R. Kunwar, M.D., MedScape CME
 "AD/HD Co-Morbidity: What's Under the Tip of the Iceberg?" 2007, Carol E. Watkins, M.D., Northern County Psychiatric Associates
"How to Treat Depression in Children with ADHD", 2006, Aug/Sept, Larry Silver, M.D, Additude Magazine
 "Treatment Resistance in Youths with ADHD and Comorbid Conditions", 2007, Oct 1, Anthony L. Rostain, M.D. MA, Psychiatric Times