**4. Materials and Methods**

This study is a literature review on the efficacy of BTX-A in bladder pain, focusing on molecular evidence and animal studies. A search for original and review articles was performed on PubMed, MEDLINE, Crossref, Embase, and Google Scholar databases using "botulinum toxin", "molecular model", "animal model", and "bladder pain" as search terms. To expand the scope of the search, we included the following terms: "interstitial cystitis", "hypersensitive bladder", "neuropathic pain", "pain management", "neurotoxin", "neurogenic bladder", and "botulinum toxin injections". This is a non-systemic review that was based on previously published articles. The search results were used to summarize current evidence for the possible molecular mechanism of action of BTX-A on bladder pain. All papers identified were English-language, full-text papers. We also checked the reference lists of selected articles to identify any papers with potentially missed data.

**Author Contributions:** Conceptualization, H.-C.K.; methodology, T.-C.Y.; writing—original draft preparation, T.-C.Y.; writing—review and editing, T.-C.Y., P.-C.C. and Y.-R.S.; supervision, H.-C.K. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Acknowledgments:** This work was greatly enhanced by Han-Chorng Kuo.

**Conflicts of Interest:** The authors declare no conflicts of interest.
