Obsessive-compulsive disorder (OCD) is characterized by recurrent, persistent, unwanted, and intrusive thoughts, urges, or images (obsessions) and/or by repetitive behaviors or mental acts that patients feel driven to do (compulsions) to try to lessen or prevent the anxiety that obsessions cause. Diagnosis is based on history. Treatment consists of psychotherapy (specifically, exposure and response prevention), drug therapy (specifically, SSRIs or clomipramine), or, especially in severe cases, both.