The evidence base for the effective treatment of personality disorders is insufficient. Most of the existing evidence on personality disorder is for the treatment of borderline personality disorder, but even this is limited by the small sample sizes and short follow-up in clinical trials, the wide range of core outcome measures used by studies, and poor control of coexisting psychopathology. Psychological or psychosocial intervention is recommended as the primary treatment for borderline personality disorder and pharmacotherapy is only advised as an adjunctive treatment. The amount of research about the underlying, abnormal, psychological or biological processes leading to the manifestation of a disordered personality is increasing, which could lead to more effective interventions. The synergistic or antagonistic interaction of psychotherapies and drugs for treating personality disorder should be studied in conjunction with their mechanisms of change throughout the development of each.

The pervasive effect of personality disorder is often overlooked in clinical practice, both as an important moderator of mental state and physical disorders, and as a disorder that should be recognised and managed in its own right. Contemporary research has shown that maladaptive personality (when personality traits are extreme and associated with clinical distress or psychosocial impairment) is common, can be recognised early in life, evolves continuously across the lifespan, and is more plastic than previously believed. These new insights offer opportunities to intervene to support more adaptive development than before, and research shows that such intervention can be effective. Further research is needed to improve classification, assessment, and diagnosis of personality disorder across the lifespan; to understand the complex interplay between changes in personality traits and clinical presentation over time; and to promote more effective intervention at the earliest possible stage of the disorder than is done at present. Recognition of how personality disorder relates to age and developmental stage can improve care of all patients.

Personality disorders are common and ubiquitous in all medical settings, so every medical practitioner will encounter them frequently. People with personality disorder have problems in interpersonal relationships but often attribute them wrongly to others. No clear threshold exists between types and degrees of personality dysfunction and its pathology is best classified by a single dimension, ranging from normal personality at one extreme through to severe personality disorder at the other. The description of personality disorders has been complicated over the years by undue adherence to overlapping and unvalidated categories that represent specific characteristics rather than the core components of personality disorder. Many people with personality disorder remain undetected in clinical practice and might be given treatments that are ineffective or harmful as a result. Comorbidity with other mental disorders is common, and the presence of personality disorder often has a negative effect on course and treatment outcome. Personality disorder is also associated with premature mortality and suicide, and needs to be identified more often in clinical practice than it is at present.