The aim of this study was to verify whether the use of bethanechol during radiotherapy (RT) for head and neck cancer (HNC) prevents radiation-induced xerostomia and salivary flow reduction. Patients that would begin RT were randomly allocated into bethanechol (group 1) or artificial saliva (group 2). Whole resting saliva (WRS) and whole stimulated saliva (WSS) were collected from all the patients at the following four stages: baseline, during, immediately after, and at least two months after the end of RT. Xerostomia was assessed by a subjective visual analogue scale (VAS), and by asking patients whether they felt dry mouth. Forty-three patients were randomized into this trial. The use of bethanechol during RT for HNC cancer was associated with significantly higher WRS immediately after RT (p=0.03) in comparison to a similar cohort of patients who had not received bethanechol.