BackgroundResearch on the impact of ethics reflection groups (ERG) (also called moral case deliberations (MCD)) is complex and scarce. Within a larger study, two years of ERG sessions have been used as an intervention to stimulate ethical reflection about the use of coercive measures. We studied changes in: employees’ attitudes regarding the use of coercion, team competence, user involvement, team cooperation and the handling of disagreement in teams.MethodsWe used panel data in a longitudinal design study to measure variation in survey scores from multidisciplinary employees from seven departments within three Norwegian mental health care institutions at three time points (T0–T1–T2). Mixed models were used to account for dependence of data in persons who participated more than once.ResultsIn total, 1068 surveys (from 817 employees who did and did not participate in ERG) were included in the analyses. Of these, 7.6% (N = 62) responded at three points in time, 15.5% (N = 127) at two points, and 76.8% (N = 628) once. On average, over time, respondents who participated in ERG viewed coercion more strongly as offending (p< 0.05). Those who presented a case in the ERG sessions showed lower scores on User Involvement (p< 0.001), Team Cooperation (p< 0.01) and Constructive Disagreement (p< 0.01). We observed significant differences in outcomes between individuals from different departments, as well as between different professions. Initial significant changes due to frequency of participation in ERG and case presentation in ERG did not remain statistically significant after adjustment for Departments and Professions. Differences were generally small in absolute terms, possibly due to the low amount of longitudinal data.ConclusionsThis study measured specific intervention-related outcome parameters for describing the impact of clinical ethics support (CES). Structural implementation of ERGs or MCDs seems to contribute to employees reporting a more critical attitude towards coercion. Ethics support is a complex intervention and studying changes over time is complex in itself. Several recommendations for strengthening the outcomes of future CES evaluation studies are discussed. CES evaluation studies are important, since—despite the intrinsic value of participating in ERG or MCD—CES inherently aims, and should aim, at improving clinical practices.Supplementary InformationThe online version contains supplementary material available at 10.1186/s12910-023-00909-w.