["Addiction, EarlyView. ", "\nAbstract\n\nAims\nThis study assessed the feasibility and acceptability of a new theory‐ and evidence‐based intervention designed to prevent return to pre‐admission smoking behaviours after discharge from a smokefree mental health in‐patient setting in the United Kingdom (UK).\n\n\nDesign\nA multi‐centre individually randomised controlled feasibility trial with follow‐up at 3 and 4–6 months.\n\n\nSetting\nAcute adult mental health wards of six National Health Service Mental Health Trusts in England.\n\n\nParticipants\nThirty‐eight (17 intervention, 21 usual care) adults who smoked on or after admission to an acute adult mental health in‐patient ward and wished to continue reducing or quitting smoking after discharge, enrolled between February and November 2024.\n\n\nIntervention\nThe intervention comprised usual care and a 12‐week, theory‐ and evidence‐informed support programme including a bespoke resource kit, personalised behavioural support including phone calls and text messages, and access to a digital smoking cessation app with 24/7 live support. It was delivered by trained mental health workers. The comparator group received usual care as per UK national guidance, typically involving brief behavioural support, offers of nicotine replacement therapy and sometimes electronic cigarettes.\n\n\nMeasurement\nPrimary outcomes included recruitment and retention, intervention acceptability and feasibility of collecting smoking, mental health and economic data. Success criteria for progression to trial were set a priori at a minimum of 60% of the n = 64 target for both recruitment and retention, i.e. at n = 38. Secondary outcomes included measures of smoking, quitting, reduction of cigarette consumption. Acceptability data were collected through exploratory interviews with participants, mental health staff and interventionists.\n\n\nFindings\nWe recruited n = 38 (60%) participants and retained n = 20 (52.6%) at 3 months, and n = 13 (34.2%) at second follow‐up. As such, criteria agreed to determine progression to full trial were marginally met for recruitment and not met for retention. Two intervention participants reported maintaining abstinence. Motivation to quit remained higher in the intervention than the usual care group over time, and use of e‐cigarettes was overall common (76.9% n = 10 across groups at 4–6 month follow up). Intervention group participants reported valuing the tailored and personalised behavioural support options but engaged little with tailored digital tools. Health economic data collection was feasible, though refinement is needed for future research.\n\n\nConclusions\nA new intervention delivering smoking cessation support to individuals discharged from smoke‐free mental health settings was discontinued because key feasibility criteria were not met, highlighting the need for focused reconsideration of recruitment and retention strategies, intervention design and delivery in mental health in‐patient populations. Design implications are discussed, taking into account individual patient‐level and systemic challenges.\n\n"]