Background: The effects of Glucagon-like peptide-1 (GLP-1) Receptor Agonists (RA), such as Ozempic, are not well understood in patients undergoing cancer treatments. Methodology: A 73-year-old man, with a background of type 2 diabetes and obesity being treated with Ozempic, was diagnosed with a nasopharyngeal carcinoma. Ozempic was ceased prior to chemo-radiotherapy. During treatment, the patient required nasogastric tube feeding for weight loss and developed refeeding syndrome. Results: The refeeding syndrome presented as hypophosphatemia of four weeks’ duration, with hypokalaemia, hypomagnesemia, and elevated C-reactive protein. The refeeding syndrome resolved by week 2 post-treatment. There was no other significant radiotherapy- or chemotherapy-related toxicity throughout this time. Conclusion: This case is an example of a complication from usage of GLP-1 RA with concurrent chemo-radiotherapy in head and neck cancer. More clinical evidence is needed for GLP-1 RA in the context of cancer, treatment effects, nutritional status, and its withdrawal effects. Earlier interventions to support nutrition may be required for head and neck cancer patients with a history of GLP-1 RA usage.