N-of-1 trial designs in mental health: A qualitative study of their appropriateness, and barriers and facilitators to their use

Background N-of-1 designs involve randomising an individual between treatments and recording outcomes over several timepoints. They are rarely used in mental health research. This research aims to explore the reasons behind this, identifying both opportunities and barriers to their implementation. Methods A cross-sectional qualitative study was conducted to explore healthcare professionals’ and trial app developers’ views on N-of-1 trials in mental health. Data were collected through semi-structured interviews and analysed using framework analysis, informed by the Theoretical Domains Framework. Results We conducted interviews with nine participants, including three psychiatrists, two mental health nurses, two other health professionals, and two people who were involved in developing apps for research in mental health to explore perspectives on N-of-1 trials in mental health. We generated three key themes: (1) N-of-1 trial designs are appropriate for very specific combinations of patient populations, interventions and settings in mental health. (2) If used appropriately, N-of-1 trials have the potential to inform treatment choice, improve outcomes and empower patients. (3) Improved knowledge and understanding of N-of-1 trials is needed among clinicians, patients and the wider research system to facilitate the use of this trial design in mental health. Conclusions Our findings suggest a potential role for N-of-1 trials in mental health, specifically for patients with stable chronic conditions and for interventions that can be safely discontinued and re-started. N-of-1 trials could inform treatment choices, improve outcomes, and empower patients. However, significant barriers to implementing this trial design exist within the current UK health and research system.