Preferences have been shown to be influenced by initial endowments of wealth in the valuation literature. This paper tested for the influence of initial endowments of experience on preferences, using a discrete choice experiment. The experiment was carried out within the context of a randomized controlled trial evaluating the introduction of a new repeat prescribing system. The 'intervention group' experienced the proposed new system and the 'control group' the existing system. Evidence of an experience endowment effect was found, with only the 'intervention group' valuing attributes of the new repeat prescribing system. The implications of these results for economic evaluations alongside randomized controlled trials are considered.