Changes in sexual-function scores after washed microbiota transplantation in men with sexual dysfunction: an exploratory single-arm pre-post observational study.

Background and aims: Current therapies for male sexual dysfunction (MSD) exhibit variable efficacy and potential adverse effects. Washed microbiota transplantation (WMT) is an emerging microbiota-based intervention, but its clinical relevance to MSD remains unclear. This exploratory single-arm pre-post observational study aimed to describe within-subject changes in sexual function, sexual quality of life, sex hormones, and gut microbiota profiles before and after WMT in men receiving WMT for established clinical indications. Methods: A total of 37 male patients receiving WMT were enrolled, including 16 patients with baseline MSD and 21 patients with normal baseline sexual function. All participants received WMT via the lower gastrointestinal tract, and no placebo, sham, untreated, or standard-care control group was included. Sexual function and quality of life were evaluated using the Sexual Life Quality Questionnaire (SLQQ) and the Arizona Male Sexual Experience Scale (ASEX), which were designated as the primary exploratory endpoint. Serum sex hormone levels and gut microbiota profiles characterized by 16S rRNA gene sequencing were defined as secondary exploratory outcomes. The primary sexual-function analyses were based on within-subject pre-post comparisons, and no formal power calculation was performed for the secondary hormone or microbiome outcomes. Results: In within-subject analyses, favorable changes in sexual-function scores were observed at one-month follow-up in the baseline MSD group: 10 of 16 patients no longer met the ASEX-defined MSD threshold, ASEX scores decreased, and SLQQ scores increased. However, because this was an uncontrolled single-arm pre-post analysis, these changes cannot be attributed causally to WMT and may partly reflect placebo or expectancy effects, regression to the mean, natural symptom fluctuation, concurrent care, or improvement in the underlying chronic conditions for which WMT was administered. The hormone and microbiota analyses were limited by the small number of patients with baseline MSD. Therefore, the non-significant hormone findings should be interpreted as inconclusive rather than as evidence of no endocrine involvement, and the microbiota findings should be regarded as exploratory and susceptible to both type I and type II errors. Conclusion: In this exploratory single-arm pre-post observational cohort, favorable within-subject changes in sexual-function and sexual quality-of-life scores were observed at one-month follow-up after WMT. However, because the study lacked a placebo, sham-procedure, untreated, or standard-of-care control arm, these changes should not be interpreted as evidence of therapeutic efficacy. The findings are hypothesis-generating and require validation in adequately powered randomized placebo- or sham-controlled trials.