OBJECTIVES: To evaluate the cost-effectiveness of prolonged release oxycodone/naloxone combination tablets [OXN; naloxone is added to counteract opioid-induced constipation (OIC)] in patients who are constipated despite the use of two laxatives, compared with prolonged release oxycodone (OXY) alone. METHODS: A model used data from one phase II randomised, controlled trial (RCT) in patients with moderate/severe cancer pain and a pooled analysis of two phase III RCT’s in patients with moderate/severe non-cancer pain. A subgroup of patients with OIC who had failed on two or more laxatives at screening was applied in the analysis (n=178). The drug cost for pain therapy was combined with laxative costs and other resources to calculate the cost difference between OXN and OXY. Quality-adjusted life-year (QALY) gains were calculated by mapping Bowel Function Index scores to EQ-5D utility values. Deterministic sensitivity analyses were performed. The analysis was conducted from the perspective of the UK National Health Service (NHS). RESULTS: The incremental cost of OXN vs. OXY was £409.60 for the average treatment duration of 301 days. OXN gave an incremental QALY gain of 0.0524. The estimated incremental cost-effectiveness ratio (ICER) was £7,821.80 for OXN vs. OXY. The ICER remained below £30,000 for all sensitivity analyses, with OXN dominating OXY in some scenarios when higher constipation unit costs were applied. CONCLUSIONS: Patients treated with OXN experienced a quality of life gain, and OXN had an ICER considerably below thresholds normally regarded as cost-effective in the UK (£20,000 – 30,000/QALY). More research is required into the cost of treating OIC, with OXN dominating OXY (total cost saving to the NHS and quality of life benefit) in sensitivity on OIC unit costs. OXN is therefore estimated to be a cost-effective option for treating patients with moderate to severe pain and OIC, who are constipated despite the use of two laxatives.