OBJECTIVES: Cox-2 selective inhibitors have been shown to have similar efficacy but a reduced gastrointestinal (GI) side-effect profile compared to non-selective non-steroidal anti-inflammatory drugs (NSAIDs). The purpose of this study was to use conjoint analysis (discrete choice methodology) to value the reduction in risk of GI side effects with VIOXX (a Cox-2 inhibitor) when compared with non-selective NSAIDs in patients with Osteoarthritis (OA). METHODS: Eighty-five participants with OA were recruited for this project and asked to complete questions regarding demographics, their OA and GI-related symptoms and a discrete choice task. The attributes used in the willingness-to-pay (WTP) scenarios included values for risks associated with complicated perforations, ulcers and bleeds (PUBs), uncomplicated PUBs, minor GI adverse and the cost of medication to the patient. The risk estimates were derived from clinical studies between VIOXX and non-selective NSAIDs. RESULTS: Participants ranged in age from 49-83 years (mean = 64.3 years). Twelve patients were excluded because they were either non-traders (2) or irrational in their choice task (10), leaving an effective sample size of 73. The total WTP for the reduced risk of GI-complications provided by VIOXX, was $A57.85 per month (95% CI:22.09-98.34). This included a WTP of $A36.27 and $A38.43 for the reduced risk offered by VIOXX of uncomplicated and complicated PUBs, respectively. For minor GI events, the difference between the levels was not statistically different from zero, indicating that no difference was seen between the levels by the respondents. The point estimate from this attribute produced a negative WTP (-$A16.85) that was included in the overall estimate of WTP.CONCLUSIONS: The results from this study illustrate the value that OA patients attribute to the reduction in GI-side effects associated with Cox-2 selective inhibitors such as VIOXX. On average, patients were willing to pay $A57.85 per month for a medication that specifically reduced the risk of both complicated and uncomplicated PUBs.