Prevalence and predictors of mental incapacity in psychiatric in-patients.

BACKGROUND Little is known about the proportion of psychiatric in-patients who lack capacity to make treatment decisions, or the associations of lack of capacity. AIMS To determine the prevalence of psychiatric in-patients who lack capacity to make decisions about current treatment and to identify demographic and clinical associations with lack of mental capacity. METHOD Patients (n=112) were interviewed soon after admission to hospital and a binary judgement of capacity was made, guided by the MacArthur Competence Tool for Treatment. Demographic and clinical information was collected from an interview and case notes. RESULTS Of the 112 participants, 49 (43.8%) lacked treatment-related decisional capacity. Mania and psychosis, poor insight, delusions and Black and minority ethnic group were associated with mental incapacity. Of the 49 patients lacking capacity, 30 (61%) were detained under the Mental Health Act 1983. Of the 63 with capacity, 6 (9.5%) were detained. CONCLUSIONS Lack of treatment-related decisional capacity is a common but by no means inevitable correlate of admission to a psychiatric in-patient unit.