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Bibliographic Details
Main Authors: Farinhas, António, Guerreiro, Nuno M., Pombal, José, Martins, Pedro Henrique, Melton, Laura, Conway, Alex, Dochat, Cara, D'Eon, Maya, Rei, Ricardo
Format: Preprint
Published: 2026
Subjects:
Online Access:https://arxiv.org/abs/2602.00950
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Table of Contents:
  • Large language models are increasingly used for mental health support, yet their conversational coherence alone does not ensure clinical appropriateness. Existing general-purpose safeguards often fail to distinguish between therapeutic disclosures and genuine clinical crises, leading to safety failures. To address this gap, we introduce a clinically grounded risk taxonomy, developed in collaboration with PhD-level psychologists, that identifies actionable harm (e.g., self-harm and harm to others) while preserving space for safe, non-crisis therapeutic content. We release MindGuard-testset, a dataset of real-world multi-turn conversations annotated at the turn level by clinical experts. Using synthetic dialogues generated via a controlled two-agent setup, we train MindGuard, a family of lightweight safety classifiers (with 4B and 8B parameters). Our classifiers reduce false positives at high-recall operating points and, when paired with clinician language models, help achieve lower attack success and harmful engagement rates in adversarial multi-turn interactions compared to general-purpose safeguards. We release all models and human evaluation data.