“…Opioid analgesics remain the cornerstone of treatment for cancer patients with moderate to severe pain and morphine is still the gold standard among commonly used opioids (Foley, 2000;Ruan, 2007;Ross and Hahn, 2008), although using opioids to manage chronic noncancer pain is controversial (Maier et al, 2002). When morphine is used for patients with chronic pain, however, duration of morphine administration is usually long enough to allow for the development of morphine tolerance and dependence (Foley, 2000;Maier et al, 2002;Meldrum, 2003;Ross and Hahn, 2008). Therefore, exploring effective measures to prevent these undesirable adverse effects seems to be of great clinical relevance.…”