A Cochrane review [withdrawn from publication] summarises the evidence on opioid switching. Significant minority of patients with chronic pain requiring strong opioids either suffer intolerable side-effects, inadequate pain relief, or both. For these patients switching to an alternative opioid is becoming established clinical practice. Fifty-two uncontrolled studies were identified, comprising 23 case reports, 15 retrospective studies/audits and 14 prospective uncontrolled studies. The majority of the reports used morphine as first-line opioid and the most frequently used second-line opioid was methadone. All reports, apart from one, concluded that opioid switching is a useful clinical manoeuvre for improving pain control and/or reducing opioid-related side-effects. It is unclear whether the improved outcome post-switch is a true drug effect, or merely improved tolerability as a result of dose reduction. Bias towards reporting only positive findings is obvious.