The male hormone testosterone is important for sexual and reproductive development but it can also make men less likely to question their impulses, suggests new research.

Men given doses of testosterone performed more poorly on a test designed to measure cognitive reflection than a group given a placebo, showed the findings of a study to be published in an upcoming issue of the journal Psychological Science. The findings suggest that the sex hormone is connected with greater reliance on gut instincts and less self-reflection.

 "What we found was the testosterone group was quicker to make snap judgments on brain teasers where your initial guess is usually wrong," said Colin Camerer, Professor at California Institute of Technology in the US. "The testosterone is either inhibiting the process of mentally checking your work or increasing the intuitive feeling that 'I'm definitely right,'" Camerer said. The study included 243 males who were randomly selected to receive a dose of testosterone gel or placebo gel before taking a cognitive reflection test. 

The results "demonstrate a clear and robust causal effect of (testosterone) on human cognition and decision-making," the researchers said.

They believe that the phenomenon they have observed can be linked to testosterone's effect of increasing confidence in humans.  Testosterone is thought to generally enhance the male drive for social status, and recent studies have shown that confidence enhances status.

"We think it works through confidence enhancement. If you're more confident, you'll feel like you're right and will not have enough self-doubt to correct mistakes," Camerer said.  The results of the study raise questions about potential negative effects of the growing testosterone-replacement therapy industry, which is primarily aimed at reversing the decline in sex drive many middle-aged men experience, Camerer said."If men want more testosterone to increase sex drive, are there other effects? Do these men become too mentally bold and thinking they know things they don't?" Camerer asked.