A double-blind randomized controlled trial to verify the improvement effect of Hangeshashinto on oral mucositis and blood metabolome analysis to clarify biomarkers, Kampo medicine's proof, and to contribute to appropriate use of Kampo medicines

INTERVENTION: Gargling with hangeshashinto and oral administration during head and neck chemoradiotherapy Gargling with placebo and oral administration during head and neck chemoradiotherapy CONDITION: Head and Neck cancer PRIMARY OUTCOME: Duration time of oral mucositis (DTM) of grade 2 or higher oral mucositis (assessed by CTCAE V5.0) during head and neck chemoradiation therapy. SECONDARY OUTCOME: The incidence of Grade 2 or higher oral mucositis (IOM) during head and neck chemoradiation therapy. Note that the grade is not the average intraday variation, but the worst grade within the day.; Time to healing of oral mucositis (THM); Adverse events other than oral mucositis (oral bleeding, oral infectious complications, etc.) (frequency, severity); Influence on treatment of primary disease; Proportion of discontinuation of radiotherapy; Percent reduction in chemotherapy intensity; Nutritional evaluation; Content and amount of oral intake; Percentage requiring nutritional management such as enteral nutrition through gastrostomy or high‐calorie transfusion; Percentage of weight loss, percentage of decrease in blood prealbumin level; Metabolome analysis in blood; Chronological and exhaustive search for minute metabolites in blood; Safety evaluation of hangeshashinto and placebo; Presence or absence and frequency of adverse events due to the use of the study drug. INCLUSION CRITERIA: