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The purpose of this paper is to determine whether prophylactic gabapentin usage in patients undergoing definitive concurrent chemotherapy and radiation therapy (chemoRT) for oropharyngeal cancer (OPC) improves treatment-related oral mucositis pain, opioid use, and feeding tube (FT) placement.This double-blind, randomized phase 3 study for patients with locally advanced OPC undergoing chemoRT randomly allocated patients to prophylactic gabapentin (600 mg thrice daily) or placebo. The primary endpoint was change in Patient-Reported Oral Mucositis Symptom (PROMS) scores over the entire treatment period (baseline to 6 weeks post-radiation therapy [RT] follow-up) with higher scores indicating worse outcomes. Opioid requirements, FT placement, and other patient-reported quality of life (QOL) metrics (Functional Assessment of Cancer Therapy-Head and Neck [FACT-HN] and Patient-Reported Outcomes version of the National Cancer Institute Common Terminology Criteria for Adverse Events [PRO-CTCAE]) were assessed. Lower scores suggested poorer QOL with the FACT-HN questionnaire, and higher scores suggested worse outcomes with the PRO-CTCAE questionnaire. Questionnaires were administered at baseline, weekly during RT, and at 6 weeks post-RT follow-up. Repeated measures analysis of variance was used to detect differences in PROMS scores and change in opioid use from baseline. Wilcoxon rank sum tests were used to compare averages for the other secondary endpoints. A P value less than .05 was considered statistically significant.Treatment arms were well balanced overall, including T and N staging and dosimetric variables. There were 58 patients analyzed. No significant difference was found in PROMS scores (mean 29.1, standard deviation [SD] 22.5 vs 20.1, SD 16.8 for gabapentin vs placebo, respectively, P = .11). The FACT-HN functional well-being index had a significant decrease in scores from baseline to follow-up in the gabapentin arm (median -6, interquartile range [IQR] -10.0 to -0.5 vs -1, IQR -5.5 to 3.0, P = .03). PRO-CTCAE scores increased significantly at follow-up for gabapentin (median 6.5, IQR 3.5-11.8 vs 1, IQR -2.0 to 6.0, P = .01). There was no significant difference in average or change in opioid use. FT placement was significantly higher in the gabapentin arm (62.1% vs 20.7%, P.01).This study suggests that prophylactic gabapentin is not effective in improving treatment-related oral mucositis symptoms in a select population of patients with OPC undergoing definitive chemoRT.