Lehe, Martin S.Martin S.Lehe0000-0003-0467-7361Halbeisen, GeorgGeorgHalbeisenSteins-Loeber, SabineSabineSteins-Loeber0000-0002-7651-0627Paslakis, GeorgiosGeorgiosPaslakis2026-03-172026-03-1720261098-108X0276-3478https://fis.uni-bamberg.de/handle/uniba/114298Objective: Eating disorders (EDs) in men are underdiagnosed and undertreated, partly due to stigma hindering help-seeking. This randomized waitlist-controlled study tested the efficacy of the iSMEsH online anti-stigma intervention targeting German general practitioners (GPs) and medical students. The program aimed to reduce stigmatizing attitudes toward men with EDs and improve knowledge and self-efficacy in managing ED symptoms. Method: A total of 292 participants (130 GPs, 162 medical students) were randomly assigned to immediate intervention or waitlist control. The intervention consisted of six video-based, on-demand modules co-developed with men who have lived experience of an ED, combining education and contact-based strategies. Outcomes included cognitive stigma (knowledge), affective stigma (biased attitudes), and behavioral stigma (treatment self-efficacy), assessed at three timepoints. Results: The iSMEsH anti-stigma intervention significantly increased knowledge of male-specific ED presentations and enhanced treatment self-efficacy in both GP and medical student populations. Effects on affective stigma were less consistent. Discussion: Findings support the efficacy of the iSMEsH anti-stigma intervention in improving knowledge and treatment self-efficacy regarding EDs in men among healthcare professionals. Effects on affective stigma were limited and may require longer follow-up periods to be comprehensively captured. The intervention shows promise as a scalable tool to reduce stigma and improve care for men with EDs. Trial Registration: On July 1, 2024 (#181,415; https://aspredicted.org/tzds-h5yq.pdf) and a study protocol is published under Lehe et al. (2025)engaccess to careanti-stigmaeating disordersgeneral practitionerhelp seekingmalemedical staffmenprimary healthcarestigmaarticle10.1002/eat.70080