Abstract
<title>Abstract</title> <p> <bold>Background:</bold> To evaluate whether a modified injection protocol reduces pain and injection-site reactions (ISRs) to 240 mg degarelix acetate in advanced prostate cancer patients. <bold>Methods:</bold> A <bold/> single-center, prospective, randomized controlled trial was conducted. 180 patients were randomized at 1:1 to modified protocol (abdominal muscle relaxation and 1-minute slow phased injection) or standard rapid injection. Primary outcome: VAS pain score at 72 h; secondary outcomes: ISRs and patient experience. Data was collected between January 2024 and August 2025. <bold>Results:</bold> The experimental group had significantly lower 72 h VAS pain (0.9±0.5 vs 2.3±1.0, p<0.001) and milder swelling, erythema, induration, pruritus (all p<0.001). Patient satisfaction and re-treatment willingness were higher; no serious adverse events. <bold>Conclusion:</bold> The modified protocol effectively reduces pain, drug aggregation and ISRs, with good reproducibility and clinical practicality. It improves treatment experience, adherence, and provides a reference for optimizing injection of high-viscosity subcutaneous drugs. <bold>Trial registration:</bold> This trial was registered at the Chinese Clinical Trial Registry (ChiCTR2400087654) on January 1, 2024. The trial protocol was consistent with the registered version. </p>