Anxiety is a feeling of fear, worry, uneasiness, or dread. It may be associated with physical problems or drugs and is often prompted by feelings of helplessness or loss of self-esteem. Generalized anxiety disorder (GAD) is characterized by chronic excessive and uncontrollable worry about various life circumstances, often with no basis. It may be accompanied by muscle tensing, restlessness, dyspnea, palpitations, insomnia, irritability, or fatigue.

Panic disorder is a form of anxiety disorder marked by episodes of intense fear. A person with panic disorder may isolate himself or herself or avoid social situations for fear of having a panic attack or in response to attacks. A phobia is an extreme, persistent fear of a specific object or situation. It may center on social situations; particular objects, such as animals or blood; or activities, such as flying or driving through tunnels. Obsessive-compulsive disorder (OCD) is a condition marked by recurrent thoughts or images that are persistent and intrusive. To relieve anxiety about these thoughts or images, the person with OCD engages in repetitive behavior that interferes with normal daily activities, although he or she knows that such behavior is unreasonable. OCD is associated with perfectionism and rigidity in behavior.

Attention deficit–hyperactivity disorder (ADHD) is difficult to diagnose because many of its symptoms overlap or coexist with other behavioral disorders. ADHD commonly begins in childhood and is characterized by attention problems, easy boredom, impulsive behavior, and hyperactivity. ADHD has been correlated with alterations from the norm in brain structure and metabolism. It is treated with stimulant drugs, primarily methylphenidate (Ritalin).

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