Abstract Objective Carers play an important role within the UK mental health system. Those carers who support persons with psychosis can experience a reduction in their own physical and mental health. As part of the Caring for Caregivers (C4C) trial, we piloted a writing intervention (Positive Written Disclosure) that has been shown to improve wellbeing in other populations. Although we reached our recruitment target, we encountered several barriers that made recruitment slower than anticipated. This paper synthesises the process data collected during the C4C trial that relates to the barriers to recruiting and retaining psychosis carers. Results We encountered four main carer-specific barriers to the recruitment and retention of participants in our study. These were: (1) poor relationship with mental health clinicians, (2) conflicting with the care recipient’s (CR) needs, (3) lack of spare time, and (4) lack of services for mental health carers. The interventions to assist carers need to be informed by robust evidence and this requires trials that reach their recruitment targets. By sharing our practical experiences other researchers and clinicians can modify their practices to minimise recruitment difficulties and delay. Trial registration ISRCTN79116352. Retrospectively registered (before the final participant was recruited) on 23rd January 2017