BACKGROUND: Sexual dysfunction is common among people who are prescribed antipsychotic medication for psychosis. Sexual dysfunction can impair quality of life and reduce treatment adherence. Switching antipsychotic medication may help, but the clinical effectiveness and cost-effectiveness of this approach is unclear. OBJECTIVE: To examine whether or not switching antipsychotic medication provides a clinically effective and cost-effective method to reduce sexual dysfunction in people with psychosis. DESIGN: A two-arm, researcher-blind, pilot randomised trial with a parallel qualitative study and an internal pilot phase. Study participants were randomised to enhanced standard care plus a switch of antipsychotic medication or enhanced standard care alone in a 1 : 1 ratio. Randomisation was via an independent and remote web-based service using dynamic adaptive allocation, stratified by age, gender, Trust and relationship status. SETTING: NHS secondary care mental health services in England. PARTICIPANTS: Potential participants had to be aged ≥ 18 years, have schizophrenia or related psychoses and experience sexual dysfunction associated with the use of antipsychotic medication. We recruited only people for whom reduction in medication dosage was ineffective or inappropriate. We excluded those who were acutely unwell, had had a change in antipsychotic medication in the last 6 weeks, were currently prescribed clozapine or whose sexual dysfunction was believed to be due to a coexisting physical or mental disorder. INTERVENTIONS: Switching to an equivalent dose of one of three antipsychotic medications that are considered to have a relatively low propensity for sexual side effects (i.e. quetiapine, aripiprazole or olanzapine). All participants were offered brief psychoeducation and support to discuss their sexual health and functioning. MAIN OUTCOME MEASURES: The primary outcome was patient-reported sexual dysfunction, measured using the Arizona Sexual Experience Scale. Secondary outcomes were researcher-rated sexual functioning, mental health, side effects of medication, health-related quality of life and service utilisation. Outcomes were assessed 3 and 6 months after randomisation. Qualitative data were collected from a purposive sample of patients and clinicians to explore barriers to recruitment. SAMPLE SIZE: Allowing for a 20% loss to follow-up, we needed to recruit 216 participants to have 90% power to detect a 3-point difference in total Arizona Sexual Experience Scale score (standard deviation 6.0 points) using a 0.05 significance level. RESULTS: The internal pilot was discontinued after 12 months because of low recruitment. Ninety-eight patients were referred to the study between 1 July 2018 and 30 June 2019, of whom 10 were randomised. Eight (80%) participants were followed up 3 months later. Barriers to referral and recruitment included staff apprehensions about discussing side effects, reluctance among patients to switch medication and reticence of both staff and patients to talk about sex. LIMITATIONS: Insufficient numbers of participants were recruited to examine the study hypotheses. CONCLUSIONS: It may not be possible to conduct a successful randomised trial of switching antipsychotic medication for sexual functioning in people with psychosis in the NHS at this time. FUTURE WORK: Research examining the acceptability and effectiveness of adjuvant phosphodiesterase inhibitors should be considered. TRIAL REGISTRATION: Current Controlled Trials ISRCTN12307891. FUNDING: This project was funded by the National Institute for Health Research (NIHR) Health Technology Assessment programme and will be published in full in Health Technology Assessment; Vol. 24, No. 44. See the NIHR Journals Library website for further project information.