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Chapter 8 200 0% 20% 40% 60% 80% 100% Probability small�intestinal release peppermint oil cost�effective compared to placebo Cost�effectiveness threshold (€) Figure 8.3 Cost-effectiveness acceptability curve of costs and abdominal pain responder (FDA definition). The line indicates the probability (y-axis) of small-intestinal release peppermint oil being cost- effective. At a WTP-threshold of 5.000, small-intestinal release has a probability of 89% of being cost effective when using the main clinical parameter, abdominal pain responder, as effect outcome. When using uncorrected (for baseline differences) QALYs, peppermint oil is dominant in 51% of simulations and more effective at higher cost in 40% of simulations. When comparing uncorrected (for baseline differences) QALYs to corrected ones, the probability of peppermint oil being a cost-effective treatment at a WTP-threshold of €10.000 increases slightly from 56% to 58%. When assessing cost-effectiveness from a healthcare perspective, small-intestinal peppermint oil is dominant compared to placebo in 65% of ICER simulations. Peppermint oil then has a 85% probability of being cost-effective at a WTP-threshold of €10.000. Discussion Here, we report the results of the first trial-based economic evaluation of peppermint oil for IBS conducted in a multicenter, placebo-controlled RCT. The results show that