**7.1 Pain management for oral cancer patients**

Cancer pain may result from direct invasion cell of cancer into the nerve or bone tissue in the end stages of oral cancer and its management is critical issue [113]. Opioid analgesics are usually prescribed for controlling oral cancer-related pain. In spite of high dosages of opioids are prescribed, high level of cancer pain is usually poorly controlled. Switching is often necessary due to different side effects or tolerance of opioids. Methadone has been widely prescribed to manage oral pain because of its exclusive properties (e.g., long duration of action strong, high bioavailability, and analgesic effect) [114].
