The intersection between the Assisted Decision-making (Capacity) Act 2022 (ADMCA) and the Mental Health Act, 2001 (MHA) has prompted considerable debate. Although not alone in its differential treatment of mental health and physical health advance healthcare directives (AHDs), Ireland is unique in affording legally binding status to mental health AHDs for some but not all inpatient service users detained under mental health legislation. As such, in this study we aim to compare groups of service users for which AHDs would be binding or not at point of detention and to track changes in binding status over the course of admission.

This is a retrospective observational study examining involuntary admissions to a 36 bedded acute psychiatric unit in Dublin from 2021 to 2023. Admissions were grouped into those initially detained on grounds of risk or on the treatment criterion alone, as this would determine binding status of a mental health AHD. We also examined changes to binding status over the course of admission to calculate median bed days when a service user would be entitled to a binding AHD. Descriptive statistics and inferential testing (Chi-squared and Mann–Whitney U) were used to analyse the data.

Of 287 admissions of 212 service users, 73.9% admissions were under the treatment criterion alone and would therefore qualify for a binding AHD. We found that diagnosis, mode of detention, and service division were significantly associated with AHD binding status. Service users would qualify for binding AHDs on 83.6% of involuntary bed days and, of those admissions affirmed by the first tribunal, 89.9% would qualify for binding AHDs in the days afterward.

Most involuntary service users would qualify for a legally binding AHD under the ADMCA for at least part of their admission. Should AHDs become common practice, binding AHDs will play a significant role in inpatient psychiatric care.