Personality disorders and defence mechanisms

• A personality disorder is an enduring pattern of thinking, feeling, behaving and relating to others that is markedly different from what is expected in a person's culture, is inflexible and pervasive, begins by early adulthood and causes distress or impairment.
• The ten disorders are grouped into three clusters: cluster A looks odd or eccentric, cluster B dramatic, emotional or erratic, and cluster C anxious or fearful.
• No personality disorder has an approved drug treatment for its core features. Psychotherapy is the main treatment, while medication is reserved for comorbid conditions or short-term crises.
• The best studied disorder is borderline personality disorder, which can remit, and for which structured psychotherapies such as dialectical behaviour therapy are the most useful interventions.
• People with these disorders also use defence mechanisms. These are largely unconscious strategies for managing anxiety, running from immature forms such as splitting and projection towards mature forms such as humour and sublimation.

By the end of this page you should be able to:

1. Define a personality disorder and distinguish the three clusters, naming the disorders in each.
2. Explain the epidemiology and the known risk factors for personality disorders, especially borderline personality disorder.
3. Describe the biological and developmental reasoning behind these disorders.
4. Describe how defence mechanisms are arranged from immature to mature and why this matters in clinical practice.
5. Assess a patient for a personality disorder and name the structured interviews and rating scales.
6. Differentiate borderline personality disorder from mood disorders, post-traumatic stress disorder, bipolar disorder and the other personality disorders.
7. Outline the management of borderline and antisocial personality disorder following the named guidelines.
8. Recognise the prognosis and the implications for children, pregnancy and older adults.

Personality is the enduring way a person perceives, thinks about and relates to themselves and the world. Normal traits such as extroversion or caution are not disorders. They become a disorder only when the pattern is rigid, maladaptive and damaging. The pattern must not be better explained by another mental disorder, substance use or a general medical condition.

The diagnosis rests on longitudinal observation rather than a single interview. Personality functioning has several layers: traits such as temperament, characteristic ways of adapting and pursuing goals, a narrative sense of self and the dynamics of close relationships. Traits that are healthy and traits that are disturbed lie on a continuum rather than being in separate categories. This is one reason why categorical diagnoses of personality disorder are debated, and why both the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, Text Revision (DSM-5-TR) and the International Classification of Diseases, 11th revision (ICD-11) are moving towards more dimensional descriptions.

The DSM-5-TR retains ten specific personality disorders and groups them into three clusters, with a general personality disorder diagnosis for patterns that do not fit neatly. It also contains an alternative dimensional model for further study.

ICD-11 replaces the ten categories with a single diagnosis of personality disorder, rated as mild, moderate or severe, described using five trait domain specifiers (negative affectivity, detachment, dissociality, disinhibition and anankastia). An optional borderline pattern specifier is included because of its clinical utility and research base. In ICD-11, the equivalent of borderline personality disorder is therefore a personality disorder, usually moderate or severe, with the borderline pattern specifier.^[2]

The clustering is based on descriptive similarity rather than on proven shared cause. The disorders are described in the table below.^[1]

Cluster A

• Paranoid personality disorder is a pervasive distrust of others, read as malevolence without adequate evidence; suspiciousness, reluctance to confide, and grudge-bearing are common. Prevalence estimates vary across community studies (about 0.5 to 4.5%); the review cited here reported about 2.4%.^[1]
• Schizoid personality disorder is detachment from relationships, restricted emotional expression and a preference for solitary life; it affects about 0.8 to 3.1% of the general population, and sex distribution is uncertain, with some studies reporting a slight male excess and others no difference.^[1]
• Schizotypal personality disorder mixes acute discomfort in relationships with cognitive or perceptual distortions and eccentric behaviour, and overlaps genetically with schizophrenia.

Cluster B

• Antisocial personality disorder is a persistent pattern of disregarding and violating the rights of others, with deceit, impulsivity and a lack of remorse, usually evident from childhood or early adolescence onward.
• Borderline personality disorder is the commonest focus of treatment and research, and is described in detail below.
• Histrionic personality disorder is pervasive attention seeking and exaggerated emotionality, with rapidly shifting, shallow affect.
• Narcissistic personality disorder is grandiosity, a need for admiration and a lack of empathy, with fragile self-esteem underneath the grand presentation. Prevalence is about 6.2% overall, higher in men than in women.^[1]

Cluster C

• Avoidant personality disorder is social inhibition, feelings of inadequacy and hypersensitivity to negative evaluation; prevalence estimates range roughly 1.5 to 5% depending on method, with most major reviews around 1.5 to 2.5%.^[1]
• Dependent personality disorder is an excessive need to be taken care of, with submissive and clinging behaviour; prevalence is about 0.5%.^[1]
• Obsessive-compulsive personality disorder is preoccupation with orderliness, perfectionism and control at the expense of flexibility; a US survey reported 7.78%, the highest prevalence among the personality disorders in that survey, although community estimates overall range from about 2 to 8%.^[1]

Prevalence estimates for individual disorders come from community surveys and vary by country and method.

Community estimates vary by method and country. A WHO-endorsed review gives about 6.1% for any personality disorder, and 3.6%, 1.5% and 2.7% for clusters A, B and C respectively.^[1] An Indian clinical guideline that follows DSM criteria cites about 6% for any personality disorder and about 1.5% for cluster B as a whole.^[2] Global pooled estimates from a larger meta-analysis are closer to 3.8%, 2.8% and 5.0%, so the cluster figures depend strongly on instrument and method. Cluster medians in older community reviews were higher, which shows how much the figure depends on the instrument used.

• About 6% of the general population meet criteria for a personality disorder using the DSM criteria.^[2]
• Personality disorders are more common in young adulthood than later life, and are linked to male sex, unemployment, low educational attainment and previous marriage in some clusters.^[1]
• Personality disorders are clearly more common in clinical settings than in the community. The rate in general psychiatric inpatients is far higher, and in one large review borderline personality disorder alone accounts for roughly 20% of psychiatric inpatients.^[2]

Borderline personality disorder. Estimates of its prevalence range from roughly 0.5 to 5.9% of the general population.^[1] A US release based on the APA practice guideline puts it at 1.4 to 2.7% of the US population.^[5] High-quality European studies report 0.7%.^[2] It occurs in about 6% of primary care patients, usually presenting with physical symptoms, and many more people with the disorder are in contact with primary care than are identified.^[2] It is more common in young adults, women and people with low income or education.^[2]

Antisocial personality disorder. It is identified much more often in male, forensic and substance use populations than in the community. Between 20% and 55% of people with substance use disorders meet criteria, although reviews of other samples report roughly 14 to 50%, and reported rates are high among people in conflict with the law and among people who have attempted suicide.^[2]

Personality disorders do not have a single cause. The general model is an interaction between an abnormal temperament, which is substantially heritable, and an adverse environment, especially early attachment disruption and childhood adversity. Having a personality disorder is not a consequence of bad parenting alone.^[1]

• Heritability varies by disorder but is substantial. Published estimates include roughly 35 to 69% for borderline personality disorder (independent twin studies often report 35 to 45%), about 50 to 80% for psychopathic traits in the review cited here (independent twin and meta-analytic estimates are closer to 40 to 60%), about 77% in clinical samples (and about 24% in the community) for narcissistic personality disorder, and 27 to 77% for obsessive-compulsive personality disorder. Heritability for cluster A disorders is also substantial, although estimates vary with the samples and instruments used.^[1]
• Temperament refers to biologically based skills in regulating emotion. Traits such as emotional stability, conscientiousness and social dominance change over the life course, increasing until the third or fourth decade. Traits of healthy and disturbed personalities form a continuum.^[2]
• Childhood antecedents. Early internalising symptoms such as anxiety or depression in girls can predict later borderline personality disorder through a complication model, while externalising symptoms such as conduct problems in adolescence can predict it through an exposure model.^[2]
• Specific risk factors for borderline personality disorder include heritable factors, organic and neurocognitive factors such as childhood attention deficit hyperactivity disorder, pregnancy and birth complications, maternal smoking, childhood emotional abuse and neglect, prolonged separations from parents in the preschool years, and lower socioeconomic status. Heightened rejection sensitivity is linked to emotional neglect. Sexual abuse on its own increases the risk of borderline personality disorder little or not at all. Anxiety sensitivity and hostility independently increase risk.^[2]
• Neurobiology. In borderline personality disorder, serotonin function is disrupted in fronto-limbic circuits, and reductions in the volume of the hippocampus and amygdala may relate to childhood maltreatment and severity. More broadly, genetic studies implicate the serotoninergic and dopaminergic systems, and neuroimaging studies implicate the frontal and temporal lobes and the limbic-paralimbic system in personality pathology.^[1][2]
• No modifiable risk factors are established that prevent the disorder in an individual adult. Parental guidance programs and broader early-childhood interventions improve parenting and childhood behaviour problems and may reduce later behavioural disorder.^[2]

The chain runs as follows. Temperament, which is partly inherited, interacts with early environment, particularly attachment and trauma, and with neuropsychological development. This shapes how the person regulates emotion, relates to others and holds a sense of self. When these capacities fail repeatedly and rigidly, the person develops the characteristic but maladaptive interpersonal patterns of a personality disorder: for example, in borderline personality disorder, intense fear of abandonment drives frantic efforts to avoid it, splitting black-and-white images of others and sudden impulsive behaviour.

Defence mechanisms are part of this same adaptation. A person who lacks flexible, mature ways of processing conflict may rely on primitive defences such as projection or splitting, which protect the short-term sense of self but damage relationships over time.

Personality disorders present differently from episodic mental illness. The features are long-standing, pervasive across relationships and settings, and part of the person's identity rather than being perceived as foreign. Direct questioning about symptoms often meets denial; collateral history and behavioural observation are essential.

• Mood may be labile, irritable or chronically dysphoric, but it is the pattern of reactivity that matters more than severity.
• Thought content may include suspiciousness, ideas of reference, rigid perfectionism or grandiosity, depending on the disorder.
• Insight is often limited because the patterns are ego-syntonic.
• Interpersonal style can be observed during the consultation: overly charming, hostile, clingy, dramatic, guarded or emotionally flat.
• Assess risk to self and others directly but within the overall assessment rather than as a separate encounter.

Borderline personality disorder is the most studied and clinically important disorder in this group. Its core features are marked affective dysregulation, disturbed self-image and identity, unpredictable interpersonal relationships and marked impulsivity.^[2] Features are often summarised into three dimensions: impaired relatedness (chronic emptiness, unstable relationships, identity disturbance), affective dysregulation (lability, excessive anger, frantic efforts to avoid abandonment) and behavioural dysregulation (impulsivity, self-harm, suicidal behaviour).^[2]

Common presentations include:

• Frantic efforts to avoid real or imagined abandonment.
• A pattern of intense, unstable relationships that swing between idealisation and devaluation.
• Identity disturbance: a markedly and persistently unstable self-image.
• Impulsivity in at least two areas that can be self-damaging, such as spending, sex, substance use, reckless driving or binge eating.
• Repeated suicidal behaviour, gestures or threats, or non-suicidal self-injury.
• Affective instability with marked mood reactivity lasting hours to a few days.
• Chronic feelings of emptiness.
• Inappropriate, intense anger or difficulty controlling anger.
• Transient, stress-related paranoid thinking or severe dissociative symptoms.
• Splitting: others are experienced as all good or all bad, and the view can switch rapidly; people with the disorder often misread neutral faces or remarks as negative.^[2]

Affective instability is the most sensitive and specific single manifestation in psychiatric outpatients. Chronic emptiness is linked to the highest morbidity, including suicidality.^[2]

Risk and harm. Suicidal threats, gestures and attempts are common. Retrospective studies report a rate of death by suicide of roughly 8 to 12% among people with borderline personality disorder. Years of self-harm and threats may precede a completed suicide, so risk is difficult to predict and every expression must be taken seriously. Chronic risk factors include impulsivity, negative emotionality, poor functioning and chronic emptiness; acute factors include depression, substance use, an adverse life event or a recent loss.^[2]

Presentation by age. Borderline personality disorder can be diagnosed reliably in adolescence. Clinically significant features occur in about 10% of young people, and by age 16 about 1.3% meet full criteria. In people over 80 using public healthcare, prevalence is about 0.3%. In older adults the diagnosis is complicated by cognitive change, frontal or temporal degenerative disease and chronic depression, which can mimic it.^[2]

Settings. In the emergency department people present with self-harm, panic, dissociation or aggression; in outpatient clinics with relationship crises, comorbid disorder or court or employer referral; in inpatient settings the high prevalence of the disorder makes routine assessment important.^[2]

Antisocial personality disorder is characterised by a pervasive disregard for and violation of the rights of others from childhood or early adolescence. A full assessment covers antisocial behaviour, personality functioning, coping, strengths and vulnerabilities, comorbid mental disorders (including depression, anxiety, substance misuse, post-traumatic stress disorder and other personality disorders), need for psychological and social support, occupational rehabilitation and domestic violence.^[4] It is strongly comorbid with substance use and criminal justice contact.^[2]

Other cluster B, A and C disorders are described in the cluster sketch above; clinicians should build the same full longitudinal and collateral picture for each.

Anna Freud's early work established that a defence can be adaptive or maladaptive depending on the ego's maturity and flexibility. George Vaillant developed an empirical hierarchy of defensive maturity, linking mature defences to long-term psychological and social adjustment.^[6] In modern transdiagnostic models, defences are viewed as regulators of emotion and self-coherence that operate across diagnoses rather than being tied to one.

Kernberg's spectrum relates defences to personality organisation: mature defences characterise healthy personalities; neurotic and mild image-distorting defences typify neurotic structures; immature and psychotic defences are associated with borderline and psychotic organisations.^[6]

Splitting is the failure to integrate both positive and negative aspects of a person or situation, producing all-or-none thinking. It is commonly associated with borderline personality disorder. Projection attributes one's own unacceptable impulses to someone else. Acting out replaces reflection with action. Sublimation channels difficult drives into socially valued activity.

Clinically, identifying a patient's defensive style improves formulation and the therapeutic relationship, and a shift towards more mature defences predicts better outcomes across treatment orientations.^[6]

The differential for a suspected personality disorder has two parts: which other conditions could produce the same personality pattern, and which other personality disorders or cluster traits overlap.

Cluster A disorders must be distinguished from schizophrenia spectrum disorders, because transient psychotic episodes can occur in all three. Histrionic and narcissistic traits overlap and are rated by observing whether admiration-seeking or exploitativeness dominates. Avoidant and dependent disorders overlap with social anxiety.

There is no laboratory or imaging test that diagnoses a personality disorder. Diagnosis is clinical, based on longitudinal history from the patient and from informants, mental state examination and structured assessment.

A single unstructured interview is rarely adequate. Informant accounts are useful but do not necessarily increase reliability. In general or primary care, structured self-report screens such as the Personality Disorder Questionnaire (PDQ-4) support, but do not replace, clinical judgement. Assessment is complicated by current psychiatric symptoms, substance use, culture, age-related personality change and the fact that people often seek help at times of crisis.^[2]

The general diagnostic criteria must be met before assigning a specific disorder: an enduring pattern present in two or more domains (cognition, affectivity, interpersonal functioning, impulse control), inflexible and pervasive, leading to clinically significant distress or impairment, stable from at least late adolescence or early adulthood, and not better explained by another disorder. The diagnosis is confirmed more by long-term pattern than by any single symptom.

Screening and questionnaires also have a role in monitoring: structured outcome measures help track personal functioning, substance use, self-harm, depression and borderline symptoms, and the burden of symptoms can be quantified.

The overall approach is to place the person in a well-structured, consistent and hopeful programme. Crisis plans are agreed in advance. Endings and transitions are phased, because they can provoke intense reactions.

All guidelines agree that people with personality disorders must not be excluded from health or social care services because of diagnosis or behaviour, that a positive and reinforcing stance works better than a punitive one, and that comorbid disorders are treated on their own merits. People with learning or acquired cognitive impairments and personality disorders still receive the same interventions with adjustments. Any medication prescribed for comorbid conditions is reviewed for misuse, adherence and overdose risk.^[3][4]

Management follows the current NICE guideline CG78 (2009) and the APA second edition practice guideline (2024).^[3][5]

Psychotherapy is the treatment of choice.^[2] NICE advises that when offering psychological treatment one should take into account the patient's choice, severity, motivation, ability to stay within therapeutic boundaries and available support. A structured, theoretically explicit approach with supervision is essential, especially for complex and high-risk patients. Sessions are usually once or twice weekly, but the frequency is adapted to need. Brief interventions shorter than about three months specifically for borderline symptoms should not be used outside a well-structured service.^[3]

NICE specifically recommends considering a comprehensive dialectical behaviour therapy programme for women with borderline personality disorder for whom reducing recurrent self-harm is a priority.^[3] The APA recommends that a patient with borderline personality disorder be treated with a structured approach to psychotherapy that has support in the literature and targets the core features of the disorder, while noting that no single therapy emerged as a gold standard.^[5]

The commonly used evidence-based psychotherapies are:

Medication has no primary role.^[3] NICE states that drug treatment should not be used specifically for borderline personality disorder or for its individual symptoms, such as repeated self-harm, emotional instability, risk-taking or transient psychotic symptoms; antipsychotics should not be used in the medium to long term.^[3] The APA likewise finds no evidence that any pharmacotherapy treats the core symptoms, and recommends that any psychotropic treatment be time-limited, aimed at a specific measurable target symptom, adjunctive to psychotherapy, and preceded by a full review of comorbidities, prior therapies and medications; medications should be reconciled at least every six months.^{[5] [2]}

Short-term sedative medication may be used cautiously in a crisis and should not be continued longer than one week, with informed consent, a single drug at the minimum effective dose and as few tablets as possible where overdose risk is present. Antipsychotic medication is not suitable for medium- or long-term use for the personality disorder itself. Comorbid depression, anxiety or post-traumatic stress disorder is treated within a well-structured programme and major psychosis, substance dependence or severe eating disorder is referred on. Crisis management follows the patient's crisis plan: calm, non-threatening stance, empathic questioning, validating the experience, problem solving and agreed follow-up, with admission reserved for unmanageable risk. Inpatient admission should be preceded by consideration of crisis resolution or home treatment, and any admission should have an agreed purpose and end point.^[3]

NICE guideline CG77 (2009, last updated 2013) and the British Psychological Society approach emphasise prevention and engagement. No one should be excluded from services because of the diagnosis. Positive, reinforcing approaches outperform punitive ones.^[4]

Psychotherapy is the main intervention. Group-based cognitive and behavioural interventions are considered to address impulsivity, interpersonal difficulty and antisocial behaviour, including offender-focused programs such as reasoning and rehabilitation for those with a history of offending. For offenders aged 17 or younger in institutional care, such programs should be offered. Pharmacological treatment should not be routinely used for the disorder or for aggression, anger or impulsivity; medication is used for comorbid depression or anxiety in line with relevant guidelines, with attention to misuse and adherence. Drug and alcohol misuse is treated with psychological interventions and, in institutional settings, possibly specialist therapeutic communities. For psychopathy or dangerous and severe personality disorder, cognitive and behavioural interventions are adapted by extending their nature and duration, with booster sessions and close monitoring. Inpatient admission, when needed, should be brief, agreed in advance and crisis-focused.^[4]

Clusters A, B and C other than borderline and antisocial have less evidence. No standard treatment algorithm exists and, outside borderline personality disorder, there are no high-quality evidence-based psychotherapies specifically tailored to a personality disorder, although a range of CBT-, psychodynamic- and supportive-approach therapies and case management may help. Treatment often targets comorbid conditions, which frequently coexist. Medication remains adjunctive and symptom-targeted.

Refer to secondary mental health services for assessment and diagnosis when a personality disorder is suspected, particularly with repeated self-harm, marked emotional instability, risk-taking, or persistent offending behaviour. Refer urgently for risk of suicide, self-harm or violence, severe functional impairment or major psychosis and complex comorbidity. Forensic services are involved where there is a history of serious violence, predatory offending or targeting of vulnerable people.^[3][4]

• Self-harm and suicide. The most serious complication, especially in borderline personality disorder. Non-suicidal self-injury is common and signals distress; completion rates for suicide in borderline personality disorder are roughly 8 to 12%.^[2]
• Substance misuse. Very common and worsens impulsivity, mood instability and risk.
• Comorbid mental disorders. Depression, anxiety, post-traumatic stress disorder, eating disorders, bipolar spectrum disorder and brief psychotic episodes occur in about 70% of people with borderline personality disorder, and rates are high for the others too.^[2]
• Physical morbidity. Higher than in the general population, with lifestyle-related illness and frequent emergency presentations.
• Relationship breakdown, social isolation, unemployment and legal involvement. Particularly for cluster B and antisocial presentations.
• Iatrogenic harm. Unstructured care, excessive and unnecessary medication, hospital admission triggered by harm behaviour, and stigma all worsen outcomes.

Personality disorders are not universally chronic. Over half of people with borderline personality disorder no longer meet the diagnostic criteria after about five years. Self-destructiveness and identity diffusion remit fastest; impulsivity and emotional lability improve more gradually with age. Substance misuse and difficult early experience are associated with slower improvement.^[2]

Cluster C features are associated with the best long-term outcome relative to cluster B. Neurobiological research suggests shared genetic background between personality pathology and mood, stress and impulsive disorders, which partly explains the comorbidity.

Remission is usually stable once achieved, but functional and relationship difficulties can persist, particularly after age 50.

There is no established primary prevention for personality disorders, and no research base for preventing borderline personality disorder specifically. Prevention focuses on:

• Early identification and treatment of conduct problems in childhood, using parent-training and family interventions, which improve both parenting and childhood behaviour.
• Stable, nurturing caregiving and attention to attachment disruption.
• Prompt treatment of comorbid conditions in young people.

There is no population screening program. Screening in practice means an alertness to personality pathology in people with recurrent self-harm, volatile relationships, repeated emergency presentations, substance use, chronic physical complaints or treatment resistance, followed by structured assessment rather than premature labelling.

In primary care the most useful actions are to recognise the pattern, avoid unnecessary medication, provide regular time-limited appointments, set clear and consistent boundaries, take self-harm seriously and arrange referral.^[2]

Children and adolescents. Severe personality traits in adolescence predict adult disorder, but many features ameliorate with age. Borderline personality disorder can be diagnosed reliably in adolescence once the features are pervasive and stable, and early diagnosis helps mobilise support. Features can be seen as early as age 6. Younger children are usually described in terms of temperament and emerging traits rather than diagnosis. Prevention and parent-focused intervention are the priority.^[2]

Pregnancy. No data support medication for the personality disorder in pregnancy. Management is psychosocial: stabilise routines, plan for crises, coordinate care with maternity services, and avoid sedatives and antipsychotics except for short periods and clear indications. Risk assessment of the mother and the infant matters. Borderline personality disorder is common in parents and affects parenting; supporting the parenting relationship is part of care.^[2]

Older adults. Personality disorders continue into later life and can cause relationship failure even after 50. Prevalence of borderline personality disorder over 80 is low. Diagnosis is complicated by cognitive decline, frontal or temporal degenerative disease and chronic depression; longitudinal history and informant accounts become even more important, and specialist liaison is often needed.^[2]

Learning disability. Personality disorder is not usually diagnosed in moderate or severe learning disability, but people with mild learning disability retain access to the same services. Consultation with a specialist in learning disability is appropriate.^[3]

Where structured psychotherapy and specialist services are scarce, the essentials are still effective:

• A thorough longitudinal history and one or two informants is more important than any test.
• Regular, time-limited appointments with one clinician build the consistency these patients need.
• Avoid polypharmacy, benzodiazepines, high-risk toxic drugs and prescription of addictive analgesics or sedatives.
• Manage crises with the principles already listed; brief, goal-directed admission is preferable to prolonged inpatient care.
• Basic psychoeducation, problem-solving, family engagement and crisis planning require no equipment.
• Train general health and community workers in non-judgemental, consistent responses.
• Refer when there is high or persistent suicidal risk, psychosis, severe eating disorder or dangerous substance dependence.

Planned links (not yet written) include anxiety disorders, bipolar disorder, post-traumatic stress disorder, schizophrenia, substance use disorders and self-harm and suicide prevention. Prerequisite pages are none; related topics can be linked once verified topics exist.

• A personality disorder is an enduring, inflexible and pervasive pattern that deviates from cultural expectations, begins by early adulthood and causes distress or impairment.
• The ten disorders fall into three clusters: A (odd or eccentric), B (dramatic, emotional or erratic) and C (anxious or fearful).
• Population prevalence is about 6 to 10% depending on method; cluster B disorders together run at about 1.5%. ^[2][1]
• Borderline personality disorder affects roughly 0.5 to 5.9% of people generally and about 1.4 to 2.7% in the US; over half remit within five years.
• Personality disorders arise from the interaction of heritable temperament and early environment, especially attachment disruption and childhood adversity, not from bad parenting alone.
• Defences are unconscious, can be adaptive or maladaptive, and range from psychotic and immature through neurotic to mature; splitting and projection are immature defences commonly tied to personality pathology.
• Diagnosis is clinical and longitudinal, supported by structured interviews such as the IPDE and SCID-5-PD; there is no diagnostic test.
• The differential must exclude mood, psychotic, substance and medical causes, and must separate overlapping personality disorders, especially among cluster B.
• Psychotherapy is the treatment of choice and is most evidence-based for borderline personality disorder; dialectical behaviour therapy is specifically recommended for recurrent self-harm in women by NICE CG78.
• No drug treats the core features of personality disorders; drugs are used only for comorbid conditions, short periods and specific measurable target symptoms, with reconciliation at least every six months per APA.
• Crisis plans, consistent boundaries, avoidance of polypharmacy and attention to comorbidity are the practical backbone.
• Cluster-specific psychological treatment evidence is strongest for borderline and, to an extent, antisocial personality disorder.