The under treatment of cancer pain is still a major issue in both oncology and palliative medicine. The initial availability of opioids is seen as an important philosophical step forward in the pharmacological treatment of cancer pain, one for which there continues to be considerable barriers within regulatory and medical domains. Knowledge of the key pharmacological properties of the multiple opioids available will assist in both improved analgesia and side effects. Understanding the mechanisms of pain is important in terms of treatment, especially in terms of the choice of co-analgesic agents. Much of the work obtained from the study of cancer patients is applicable to the non cancer populations, as is work performed in non cancer patients with neuropathic pain.