[2606.04127] When Retrieval Doesn't Help: A Large-Scale Study of Biomedical RAG
[Submitted on 2 Jun 2026]
Title:When Retrieval Doesn't Help: A Large-Scale Study of Biomedical RAG
View a PDF of the paper titled When Retrieval Doesn't Help: A Large-Scale Study of Biomedical RAG, by Erfan Nourbakhsh and 2 other authors
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Abstract:Medical question answering is a high-stakes setting where factual errors can have serious consequences. Retrieval-augmented generation (RAG) is widely viewed as a promising solution, and prior work has reported substantial gains for large medical QA models. We revisit this assumption across a broad range of open-weight instruction-tuned models spanning 7B to 72B parameters. Across five models, ten biomedical QA datasets, four retrieval methods, and four retrieval corpora, we find that retrieval yields only small and inconsistent improvements over a no-retrieval baseline, typically within 1-2 points. In contrast, the choice of backbone model has a much larger effect than the choice of retriever or corpus, and expert and layman retrieval sources perform similarly in most settings. These results suggest that the main bottleneck is not retrieval quality alone, but the model's limited ability to use retrieved evidence effectively.
Comments: 9 Pages, accepted to BioNLP Workshop at ACL 2026
Subjects:
Computation and Language (cs.CL)
Cite as: arXiv:2606.04127 [cs.CL]
(or arXiv:2606.04127v1 [cs.CL] for this version)
https://doi.org/10.48550/arXiv.2606.04127
arXiv-issued DOI via DataCite (pending registration)
Submission history
From: Anthony Rios [view email] [v1] Tue, 2 Jun 2026 18:34:54 UTC (14,450 KB)
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