Doxepin Solution for Alleviation of Stubborn Breakthrough Pain Induced by Swallowing in Patients Receiving Radiotherapy for Nasopharyngeal Carcinoma

This trial tests whether a doxepin mouth rinse (a medicated liquid) can help reduce severe pain caused by swallowing in people with nasopharyngeal cancer (a type of head and neck cancer) who develop radiation-related mouth sores during treatment. **You may be eligible if...** - You are 18 or older with confirmed nasopharyngeal cancer - You are currently undergoing radiation or chemoradiation treatment - You have radiation-related mouth sores causing significant swallowing pain (at least 4 out of 10 on a pain scale) - You are functional enough to complete questionnaires (ECOG 0–2) **You may NOT be eligible if...** - You are allergic to doxepin or similar antidepressants (tricyclics) - You are currently using a tricyclic antidepressant or MAO inhibitor - You have untreated oral fungal infection or oral herpes - You have untreated narrow-angle glaucoma or urinary retention - You have serious heart disease or recent heart attack - You are pregnant or breastfeeding Talk to your doctor to see if this trial is right for you.