Xerostomia, the subjective complaint of dry mouth, is caused by therapeutic interventions or diseases. Nowadays, radiotherapy (RT) in patients with head and neck cancer (HNC) stands out as one of the most important causes of xerostomia. Currently available therapies for the treatment of xerostomia are still less than optimal and xerostomia still represents an unmet clinical need. In this article, we present the results of a prospective clinical study with a new product, AqualiefTM, in patients treated with curative RT with or without chemotherapy for HNC. AqualiefTM is based on two main ingredients, carnosine and karkadé, which have acid buffering and antioxidant properties. The study was performed on 30 patients, with 4 of the patients being lost during the study period. Each patient received randomly one of the two treatments, AqualiefTM or placebo, for 8 days. After a 10-day wash-out period, each patient received the other treatment for a further 8 days. The results show that AqualiefTM stimulated salivation in these patients and reduced the pH drop that was observed in an equivalent placebo-treated population of patients. Moreover, no serious, treatment-related adverse events were observed. AqualiefTM has shown positive results, although with limitations due to unsuccessful trial accrual. Therefore, it may be further investigated as a tool for the treatment of RT-related xerostomia.