About one-quarter of all American adults suffer from a mental health disorder in any given year, according to the National Institute of Mental Health (NIMH). The psychologist's handbook for diagnosis, the "Diagnostic and Statistical Manual of Mental Disorders, 4th edition" (DSM-IV), lists more than 300 disorders in its pages, reports AllPsych. Most of the listed disorders are rare, however. The most common mental disorders are anxiety disorders, mood disorders and ADHD.
Anxiety Disorders
Approximately 18 percent of American adults suffer from some form of anxiety disorder, according to the NIMH. The agency also reports that most people who have one anxiety disorder have others simultaneously. They may also suffer from depression and/or substance use disorders in addition to anxiety, says the government report Healthy People 2010. The most common form of anxiety disorder is specific phobia, which afflicts 8.7 percent of adults in America. During a specific phobia, a person fears a particular item or situation, such as dogs or being in enclosed spaces. Social phobia is also relatively common, causing people to avoid social or performance situations or else to endure them with extreme distress. The next most common anxiety disorder is post-traumatic stress disorder (PTSD), the NIMH reports. This disorder appears after a trauma, such as war or rape, and causes hyperarousal and fear of situations that are reminiscent of the trauma. Other anxiety disorders are, in order of prevalence: generalized anxiety disorder, panic disorder, obsessive-compulsive disorder (OCD) and agoraphobia.
Mood Disorders
Mood disorders are the second most common form of mental health disorder in America, affecting about 9.5 percent of adults, the NIMH reports. Mood disorders break down into two general categories: unipolar and bipolar. Unipolar disorders include major depressive disorder (MDD) and dysthymic disorder. Both involve low mood, decreased interest in activities, sleep disturbances and a lowered sense of self-worth. These symptoms are more severe yet shorter-lasting in MDD than dysthymic disorder. Healthy People 2010 notes that in developed nations, major depression causes the greatest disability in the society. Bipolar disorder involves periods of depression alternating with episodes of mania, which includes sleeping less, talking more, having racing thoughts and showing poor judgment.
Attention-Deficit Hyperactivity Disorder
Another common mental disorder is attention-deficit hyperactivity disorder (ADHD). Although it is one of the most common disorders of childhood, about 4 percent of American adults also suffer from it, the NIMH reports. Individuals with ADHD show signs of inattention, including failure to listen and follow through, and/or symptoms of hyperactivity/impulsivity, such as fidgeting and interrupting others.
