Learn To Say NO! Incorporating Model Abstention In Medical Vision-Language Models for Pharmacovigilance

Sofia Jamil, Chinmay Purushottam Bhat, Sooraj Veer R, Sriparna Saha


Abstract
Abstention is the intentional refusal of models to provide an answer. Adverse drug reactions (ADRs), which range from mild to life-threatening, are often underreported by patients in hospitals and to doctors because patients assume these are unavoidable. With the growing adoption of LLMs and vision language models (VLMs) in healthcare, patients are increasingly reaching out to these models for solutions. In such high-risk scenarios, incorrect or overconfident responses can cause unnecessary anxiety, lead patients to discontinue essential medications, or encourage inappropriate self-medication. In this work, we propose the MAD-MED, a Model Abstention approach for Drug Adverse Reaction for MEDical-VLMs. It is a training strategy to encourage models to abstain when answering would contradict the available input, exceed the model’s knowledge, or violate model ethics. In addition, we release an augmented Adverse Drug Reaction ABStention (ADR-ABS) dataset comprising image-answerable, text-answerable, and unanswerable questions to support systematic evaluation of abstention behavior. Quantitative and human evaluations confirm that our proposed MAD-MED approach improved the abstention capabilities of models considerably while keeping the generative capabilities intact in cases where the model is expected to answer.
Anthology ID:
2026.aacl-long.40
Volume:
Proceedings of the 15th International Joint Conference on Natural Language Processing and the 5th Conference of the Asia-Pacific Chapter of the Association for Computational Linguistics (Volume 1: Long Papers)
Month:
November
Year:
2026
Address:
Hengqin, China
Editors:
Yue Zhang, Ruifeng Xu, Ayu Purwarianti, Tong Rong, Jun Suzuki
Venues:
AACL | IJCNLP
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
834–848
Language:
URL:
https://aclanthology.org/2026.aacl-long.40/
DOI:
Bibkey:
Cite (ACL):
Sofia Jamil, Chinmay Purushottam Bhat, Sooraj Veer R, and Sriparna Saha. 2026. Learn To Say NO! Incorporating Model Abstention In Medical Vision-Language Models for Pharmacovigilance. In Proceedings of the 15th International Joint Conference on Natural Language Processing and the 5th Conference of the Asia-Pacific Chapter of the Association for Computational Linguistics (Volume 1: Long Papers), pages 834–848, Hengqin, China. Association for Computational Linguistics.
Cite (Informal):
Learn To Say NO! Incorporating Model Abstention In Medical Vision-Language Models for Pharmacovigilance (Jamil et al., AACL-IJCNLP 2026)
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PDF:
https://aclanthology.org/2026.aacl-long.40.pdf