This qualitative systematic review of the clinical methodology used in randomised, controlled trials of oral opioids (morphine, hydromorphone, oxycodone) for cancer pain underlines the difficulties of good pain research in palliative care. The current literature lacks placebo-controlled superiority trials. Recommendations for future research are discussed.
Bell, R. F., Wisloff, T., Eccleston, C., & Kalso, E. (2006). Controlled clinical trials in cancer pain. How controlled should they be? A qualitative systematic review. British Journal of Cancer, 94(11), 1559-1567. https://doi.org/10.1038/sj.bjc.6603162