Abstract: We revisited decisions made in the earlier version of this review and excluded five studies that were previously included. We identified one new study for this update. This review includes six studies with 388 participants. We did not identify any studies in children. The included studies differed so much in their methods and comparisons that no synthesis of results was feasible. Only one study (103 participants) specifically reported the number of participants with a given level of pain relief, in this case a reduction of at least 20% - similar in both the methadone and morphine groups. Using an outcome of 'no worse than mild pain', methadone was similar to morphine in effectiveness, and most participants who could tolerate methadone achieved 'no worse than mild pain'. Adverse event withdrawals with methadone were uncommon (12/202) and similar in other groups. Deaths were uncommon except in one study where the majority of participants died, irrespective of treatment group. For specific adverse events, somnolence was more common with methadone than with morphine, while dry mouth was more common with morphine than with methadone. None of the studies reported effects on appetite. We judged the quality of evidence to be low, downgraded due to risk of bias and sparse data. For specific adverse events, we considered the quality of evidence to be very low, downgraded due to risk of bias, sparse data, and indirectness, as surrogates for appetite, thirst and somnolence were used. There were no data on the use of methadone in children. Based on low-quality evidence, methadone is a drug that has similar analgesic benefits to morphine and has a role in the management of cancer pain in adults. Other opioids such as morphine and fentanyl are easier to manage but may be more expensive than methadone in many economies.

Plain-language summary: In this updated review we set out to estimate how well methadone worked, how many people had side effects, and how severe those side effects were – for example, whether they were so severe that participants stopped taking their methadone. In May 2016, we found just six studies with 388 adult participants. The studies were often small, and compared different preparations. For pain relief there did not seem to be much difference between methadone and morphine. For most people pain was reduced from moderate or severe to mild or no pain with methadone. Methadone is associated with some unwanted effects, mainly sleepiness, constipation, and dry mouth. These can be severe enough to stop people taking methadone. No data were available about the use of methadone in children. We would like to see more consistency in study design, and especially in study reporting, which should include information on unwanted effects and the outcome of pain reduced to tolerable levels, that is, no worse than mild pain, so that people with cancer are not bothered by pain. We rated the quality of the evidence from studies using four levels: very low, low, moderate, or high. Very low quality evidence means that we are very uncertain about the results. High quality evidence means that we are very confident in the results. The quality of the evidence was low or very low.