Gabapentin for the Reduction of Radiation Therapy Induced Pain During the Treatment of Oropharyngeal Cancer

The specific aims of this proposed study include the following: * Evaluate the reduction or delay of mucositis related pain and morbidity with the use of gabapentin in patients with stage III or IV oropharyngeal squamous cell carcinoma undergoing definitive radiation with concurrent chemotherapy as part of their cancer management, compared to standard supportive side effect mitigation - using patient reported quality of life endpoints such as the Patient-Reported Oral Mucositis Symptoms (PROMS) scale. * Assess morphine-equivalent opioid use in both treatment arms by collecting the patient's narcotic use in the previous 24-hour period at each weekly evaluation during radiation treatment. * Report on change in Speech and swallow performance, as measured by the Performance Status Scale (PSS) for Head and Neck Cancer Patients * Evaluate changes in weight from baseline throughout treatment between the two arms. * Assess feeding tube requirements during treatment. * Evaluate the adverse events associated with gabapentin. * Evaluate the severity of radiation mucositis (grade 3-4, CTCAE, v. 4)