Does a single dose of testosterone increase willingness to compete, confidence, and risk-taking in men? Evidence from two randomised placebo-controlled experiments.

The sex steroid hormone testosterone regulates aggression and display of dominance in 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 body of literature documents similar testosterone effects on behaviors related to competition and risk-taking in humans, though the findings have been mixed. Here, we report two randomised double-blind placebo-controlled testosterone administration experiments (N = 91, N = 242) designed independently by researchers in Europe and the US. Both experiments investigated the effect of a single dose of testosterone (at 4 h and 21-24 h post administration) on men's willingness to compete, confidence, and risk-taking in economic tasks. We estimate weak treatment effects that are statistically indistinguishable from zero for all behavioral outcomes across the two experiments. Our findings cast doubt on the proposition that there is an overall effect of a single dose of testosterone administration on the dimensions of economic behavior studied. If such effects existed, detecting them experimentally via pharmacological studies would require very large samples. We discuss different explanations for our results, including the possibility that context and individual difference factors moderate the effects.