BACKGROUND A large proportion of people with advanced cancer will experience moderate to severe pain. Tapentadol is a novel, centrally acting analgesic medicine acting at the μ-opioid receptor and inhibiting noradrenaline reuptake. The efficacy of tapentadol is stated to be comparable to morphine and oxycodone. OBJECTIVES To assess the analgesic efficacy of tapentadol for the relief of cancer pain in adults, and the adverse events associated with its use in clinical trials. SEARCH METHODS We searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, and EMBASE from January 2005 to July 2015, together with reference lists of retrieved papers and review articles, and two clinical trial registries. Searches started from 2005 because this covered the period during which clinical trials were conducted. We contacted the manufacturer of tapentadol in the UK to find additional trials not identified by electronic searches. We did not restrict searches by language. SELECTION CRITERIA We included randomised controlled trials (RCTs) of tapentadol compared with placebo or active controls in adults with moderate to severe cancer pain. Pain had to be measured using a validated assessment tool, and studies had to include at least 10 participants per treatment arm. DATA COLLECTION AND ANALYSIS Two review authors independently extracted data using a standard form and assessed risk of bias. We extracted available data on study design, participant details, interventions, and outcomes, including analgesic outcome measures, withdrawals, and adverse events. MAIN RESULTS We included four studies with 1029 participants. All the studies used a parallel-group design, and included an initial titration phase to determine the maximum effective and tolerated dose, followed by a maintenance phase. Tapentadol medication was taken twice daily and doses ranged from 50 to 500 mg per day. Rescue medication (morphine or oxycodone immediate-release) was available to participants in all studies.Overall, 440 participants were randomised in classically designed RCTs, and 589 participants were enrolled in enriched-enrolment, randomised-withdrawal (EERW) trials. A total of 476 participants were randomised to titration with tapentadol and 338 participants took tapentadol throughout the maintenance phase of their trial.All studies used numerical rating scores, Patient Global Impression of Change scores, and use of rescue medication as measures of efficacy, and all reported on adverse events and withdrawals.All studies enrolled fewer than 200 participants per treatment arm and were therefore at risk of overestimating efficacy. One study was terminated early due to problems with supply of rescue medication, with fewer than 20 participants enrolled per treatment arm in the maintenance phase of the trial. We judged another study at high risk of bias due to an open-label design.There were insufficient data for pooling and statistical analysis. Response rates for pain intensity were comparable across treatment groups in each study. In one EERW study, response rates were high across both treatment and placebo arms during the maintenance phase (62% tapentadol, 69% morphine, 50% placebo). For pain relief, tapentadol is no more and no less effective than oxycodone or morphine (low quality evidence).Treatment emergent adverse event rates were high, approximately 50% to 90%. The most common adverse events were gastrointestinal (nausea, vomiting, constipation) (low quality evidence). There was no advantage of tapentadol over morphine or oxycodone in terms of serious adverse events. The number of people experiencing effects on consciousness, appetite, or thirst was low. AUTHORS' CONCLUSIONS Information from RCTs on the effectiveness and tolerability of tapentadol was limited. The available studies were of moderate or small size and used different designs, which prevented pooling of data. Pain relief and adverse events were comparable between the tapentadol and morphine and oxycodone groups.