A Single Administration of Testosterone Reduces Fear-Potentiated Startle in Humans

Background Ample evidence from animal research indicates that the gonadal steroid hormone testosterone has fear-reducing properties. Human data on this topic, however, are scarce and far less unequivocal. The present study therefore aimed to scrutinize anxiolytic effects of a single dose of testosterone, using a direct physiological index of fear in humans. Methods Twenty healthy female participants were tested in a double-blind, placebo-controlled crossover design involving sublingual administration of a single dose of testosterone. Four hours after intake, we assessed effects on baseline startle and fear-potentiated startle in a verbal threat-of-shock paradigm. Results In accordance with predictions, testosterone administration resulted in reduced fear-potentiated startle, without affecting baseline startle. Conclusions This study provides direct evidence that a single dose of testosterone reduces fear in humans. The relationship of this effect to previous research on anxiolytic effects of benzodiazepines, as well as possible mechanisms of action, is discussed.