Does a Single Dose of Testosterone Increase Competitiveness, Confidence and Financial Risk-taking in Men?

The sex steroid hormone testosterone regulates behaviors such as aggression and displays of dominance in male non-human animals. According to the Challenge Hypothesis, these effects arise from context-sensitive testosterone increases that facilitate inter-male competitions over resources, status, and mates. A growing literature documents similar effects of testosterone on behaviors related to competition and risk-taking in humans, though findings to date have been mixed. Here, we report two randomized double-blind placebo-controlled testosterone administration experiments (N1 = 91, N2 = 242). The experiments were designed independently by research groups in Europe and the US, and both investigated the effect of a single dose of testosterone on men’s willingness to compete, confidence, and risk-taking—dimensions of behavior that are theoretically linked to the Challenge Hypothesis and predict important real-life outcomes such as career choice. We estimate weak effects of a single dose of testosterone which cannot be statistically distinguished from zero for any of the behavioral tasks studied across the two experiments. Our findings cast doubt on the proposition that there is an overall effect of a single dose of testosterone on the dimensions of behavior studied, and suggest that even if true effects existed, detecting them experimentally via pharmacological studies would require very large samples. We discuss different explanations for our results, in particular, the possibility that the effect of testosterone on these behaviors may depend on context and individual difference factors.