Study aim: Comparison of the effect of silymarin mouthwash with benzydamine mouthwash in the prevention of grade 3 radiation-induced acute mucositis with doses above 50 Gy in head and neck squamous cell carcinoma until the end of treatment Design: A randomized, parallel group, double-blind phase 3 controlled trial of 98 patients. Randomization was carried using Sealed Envelope website (sealedenvelope.com). Settings and conduct: The study population are head and neck squamous cell carcinoma patients of Shahid Rajaei hospital in Babolsar, who will be treated with head and neck radiotherapy for the first time. The researchers, treating physicians, and the patients are blinded Participants/Inclusion and exclusion criteria: Inclusion Criteria: patients with head and neck squamous cell carcinoma, receiving at least 50 Gy radiation to 2 of the 4 areas of the head and neck including the oral cavity, oropharynx, hypopharynx and larynx Exclusion Criteria: History of severe allergy to silymarin, benzydamine or other NSAIDs, Narcotic use in the last month (even once), History of radiation therapy to the same target areas, Presence of mucositis on admission, History of dry mouth, Proven dementia or history of uncontrolled psychiatric disease, Pregnancy, Malnutrition Intervention groups: Arm A receives Silymarin mouthwash, Arm B receives Benzydamine mouthwash Main outcome variables: Grade 3 mucositis (according to Common Terminology Criteria for Adverse Events (CTCAE) v.5