We investigated the effects of testosterone administration on aspects of decision-making within the Prospect Theory framework. Using bayesian modeling, we assessed risk-taking under framing and Endowment Effect (effect of possession). We administered 100mg testosterone to forty men in a double-blind placebo-controlled fully-randomized cross-over experiment where they participated in two tasks. One was a risktaking task with binary choices under positive and negative framing with different

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... ilities. In a second task, participants had to bid for for two categories of items, hedonic and utilitarian. We observed a significant increase in serum testosterone concentrations after transdermal application. Compared to placebo, testosterone administration increased risk-taking under the positive framing and decreased under the negative framing. The sensitivity to gain was positive in each framing. Our model showed that decision-making is jointly influenced by testosterone and the trade-off between gains and losses. Moreover, while the endowment effect was more pronounced for hedonic than for utilitarian items, the effect was independent of testosterone. The findings provide novel information for the complex modulatory role of testosterone on risk-taking. The proposed models of effects of individual differences in testosterone on risk-taking could be used as predictive models.