Introduction. Mental health systems worldwide face criticism regarding power imbalances between professionals and service users. This research examines how individuals with psychiatric diagnoses in Spain experience marginalization of their knowledge and testimony within psychiatric care settings. Drawing on Fricker's epistemic injustice framework, this study investigates patterns of testimonial and hermeneutic injustice that affect patient autonomy, treatment participation, and social citizenship. Methods. A qualitative descriptive approach was implemented. Five focus group discussions involving 32 participants diagnosed with mental health conditions were conducted. Participants were recruited from mental health activism networks, ensuring diverse experiences across different psychiatric services and treatment trajectories. Thematic analysis identified patterns of epistemic injustice in clinical encounters and broader social contexts. Results. Analysis revealed systematic patterns where participants' testimonies were devalued by mental health professionals, limiting their credibility as knowers of their own experiences. Participants described exclusion from treatment decision-making processes and inadequate opportunities to articulate experiences for which interpretive resources were unavailable. These epistemic injustices extended beyond clinical settings, creating barriers to full participation in civic and social life due to stigmatized psychiatric identities. Conclusions. Findings demonstrate that epistemic injustices constitute a significant but underrecognized dimension of mental health care quality. Addressing these injustices requires structural reforms promoting shared decision making, valuing experiential knowledge, and challenging credibility deficits assigned to psychiatric service users. Implications extend to policy development emphasizing patient-centered approaches and social inclusion strategies that recognize individuals with mental health diagnoses as legitimate epistemic agents.