Personality is an overarching organized pattern of temperament, character, and psyche that determines how a person relates to, thinks about, and behaves in their environment. Personality is constructed from childhood onwards and is considered to be a product of and interaction between genetic and environmental factors. Personality disorders (PDs) refer to a category of mental health disorders characterized by persistent patterns of maladaptive personality traits. They tend to onset in adolescence with the maturation of an individual's personality. They involve distorted thinking patterns, problems with interpersonal relationships, and difficulty with emotional control and responses. Individuals with PD have stable personalities, despite their variance from culturally typical personalities. This is a major distinguishing feature that separates PD from mental illness, for which behavioral variance is prevalent and medications can be useful in some circumstances for curtailing disadvantageous behaviors.

There are 10 recognized PDs divided into clusters A, B, and C. All 10 PDs have a combined prevalence of approximately 10% in the general population. They are associated with male sex, low socioeconomic class, and poor education, although there are different epidemiologic patterns for specific PDs. There is a very high rate of PD among patients presenting for psychiatric evaluation.

Cluster A disorders are typified by behaviors and thoughts that would be considered odd or eccentric; this cluster includes schizoid PD (detached and limited range of emotions), schizotypal PD (limited social attachments but also distorted thinking, such as magical thinking), and paranoid PD (distrustful). Such patients may present with medication noncompliance (paranoia regarding rationale for prescription) and approach their medical problems with metaphysical explanations.

Cluster B disorders are typified by excessive emotional and dramatic responses and include antisocial PD (lack of respect to rules or empathy toward others), borderline PD (impulsive behaviors along with unstable and erratic interpersonal relationships), histrionic PD (excessive emotional responses, especially in efforts to get attention), and narcissistic PD (lack of empathy to others and grandiosity). These patients might present to medical personnel after self-injurious behavior or present histories with exaggerated seriousness (eg, near-death experiences).

The Cluster C grouping includes avoidant PD (excessive shyness, poor self-image, hypersensitivity), dependent PD (passivity in decision-making and submissiveness), and obsessive-compulsive PD (a need for control and perfection). This cluster is driven by underlying anxieties. These patients may have extreme difficulty making medical decisions, often deferring to the provider or a significant other, may feel criticized by health suggestions such as losing weight, or may be inflexible to changing treatment directions in light of new data.

Patients with these disorders may have an increased risk of various general medical conditions.