Exogenous testosterone increases sensitivity to moral norms in moral dilemma judgements.

Moral dilemma judgements frequently involve decisions where moral norms and the greater good are in conflict. The current preregistered study tested the effect of the steroid hormone testosterone on moral dilemma judgements using a double-blind administration of testosterone or placebo. Counter to predictions, testosterone administration led to increased inaction in moral dilemmas where harmful actions prohibited by moral norms increase overall well-being. Using a mathematical model to disentangle sensitivity to consequences, sensitivity to moral norms and general preference for inaction versus action, analyses further revealed that testosterone administration influenced judgements by increasing sensitivity to moral norms. Exploratory analyses suggested the opposite pattern for endogenous testosterone measured at baseline, in that higher levels of endogenous testosterone were associated with lower sensitivity to moral norms. The results indicate that the role of testosterone in moral judgements is more complex than suggested by previous findings. PROTOCOL REGISTRATION: The stage 1 protocol for this Registered Report was accepted in principle on 13 November 2017. The protocol, as accepted by the journal, can be found at https://osf.io/rysbe/ .