A 56-year-old woman visited an oral surgery clinic in October X with sudden pain in the left mandible. She was diagnosed with left mandibular osteomyelitis based on head computed tomography examination findings. The pain did not reduce even with amoxicillin and loxoprofen sodium hydrate. The patient was then referred to our clinic for treatment. Hainosankyuto (7.5 g/d), loxoprofen sodium hydrate (180 mg/d), and mecobalamin (1500 μg/d) alleviated the pain. However, numbness and tingling pain in the left part of the chin increased. Pregabalin 50 mg/d was then prescribed and then increased from 50 to 100 mg/d. The patient was diagnosed with antiresorptive agent-related osteonecrosis of the jaw (ARONJ). As the pain was exacerbated by discontinuation of the hainosankyuto, it was used continuously. The patient experienced no pain, even after discontinuing the mecobalamin and pregabalin. Platycodon root in hainosankyuto promotes drainage. The patient did not show any significant swelling because she took hainosankyuto during the early stages of inflammation. In addition, the pain resolved even when only hainosankyuto was used, possibly due to the analgesic effect of platycodon root, glycyrrhiza root, and peony root. Hainosankyuto may be an effective adjunctive treatment for patients with ARONJ whose pain is difficult to control with general treatment.