“…However, for oral opioids they evaluated morphine in three studies [44][45][46], tramadol in one study [47], methadone in one study [48], extended-release oxymorphone in one study [49], controlled-release oxycodone in one study [50], as well as dihydrocodeine and buprenorphine [46]. For evaluation of effectiveness of transdermal fentanyl they included three studies [44,51,52]; however, only two studies utilized pain relief of 50% or greater as their significant criteria [44,46]. In this study, because of high withdrawal rates, they first analyzed withdrawal rates of the two most commonly cited reasons for leaving a study, namely adverse events and insufficient pain relief [37].…”