delusion

Delusion is a firmly held false belief that persists despite clear evidence to the contrary and is not culturally accepted. It is a symptom that can occur across psychiatric and medical conditions, and sometimes in nonclinical contexts.

Common forms include persecutory delusions (believing one is harmed or watched), grandiose delusions (inflated worth or power), referential delusions (events have personal meaning), erotomanic delusions (another person is in love with the individual), and somatic delusions (bodily functions or health are abnormal). Delusions may be bizarre (implausible or impossible) or nonbizarre (less implausible but still false).

Delusions are distinguished from ordinary beliefs that are shared within a culture, and from illusions or hallucinations. They are also differentiated from overvalued ideas, which are held with less rigidity and openness to revision.

Causes include genetic vulnerability and neurochemical or neuroanatomical factors, medical conditions (such as delirium or neurodegenerative diseases), substances (stimulants, cannabis, alcohol withdrawal), and severe stress. Delusions appear in schizophrenia spectrum disorders, mood disorders with psychotic features, and delusional disorder, among other conditions.

Diagnosis relies on the belief’s fixed, false nature and its resistance to contrary evidence, exceeding cultural norms. In delusional disorder, one or more delusions persist for at least one month with relatively preserved functioning and without prominent hallucinations. Other conditions are ruled out.

Treatment aims to reduce distress and improve functioning and may include antipsychotic medications, psychotherapy such as cognitive behavioral therapy for psychosis, psychoeducation, and treatment of coexisting conditions. Early intervention and safety planning are important, and prognosis varies with diagnosis and treatment responsiveness.