Objectives Searching for more effective and selective therapies for head and neck cancer, we demonstrated the therapeutic effect of boron neutron capture therapy (BNCT) to treat oral cancer and inhibit long‐term tumor development from field‐cancerized tissue in the hamster cheek pouch model. However, BNCT‐induced mucositis in field‐cancerized tissue was dose limiting. In a clinical scenario, oral mucositis affects patients’ treatment and quality of life. Our aim was to evaluate different radioprotectors, seeking to reduce the incidence of BNCT‐induced severe mucositis in field‐cancerized tissue. Materials and Methods Cancerized pouches treated with BNCT mediated by boronophenylalanine at 5 Gy were treated as follows: control: saline solution; Hishigh: histamine 5 mg kg−1; Hislow: histamine 1 mg kg−1; and JNJ7777120: 10 mg kg−1. Results Hislow reduced the incidence of severe mucositis in field‐cancerized tissue to 17% vs CONTROL: 55%; Hishigh: 67%; JNJ7777120: 57%. Hislow was non‐toxic and did not compromise the long‐term therapeutic effect of BNCT or alter gross boron concentration. Conclusion: Histamine reduces BNCT‐induced mucositis in experimental oral precancer without jeopardizing therapeutic efficacy. The fact that both histamine and boronophenylalanine are approved for use in humans bridges the gap between experimental work and potential clinical application to reduce BNCT‐induced radiotoxicity in patients with head and neck cancer.