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Testosterone has long been linked to risk-taking, generosity, and competitiveness. But a new large-scale study—the biggest of its kind—finds that men given testosterone made the same economic choices as those given a placebo. The study, led by researchers at the Stockholm School of Economics in Sweden and Nipissing University in Canada, examined things like men's inclination to take risk, act fairly or compete with others.

"Earlier studies, often based on small samples, suggested that testosterone might impact our willingness to take risk or compete in economic settings," says co-lead author Anna Dreber, Professor at the Department of Economics at SSE.

"But in this substantially larger experiment, where we have also preregistered how we would do the analysis prior to observing the data to avoid bias, we do not find any effects of testosterone on economic decision making. Our findings give us strong evidence that short-term testosterone boosts don't meaningfully change men's economic choices."

Published in the Proceedings of the National Academy of Sciences, the included 1,000 men—10 to 20 times more than typical prior studies—between 18 to 45 years old who were recruited between 2018 and 2023 at three locations in Canada.

Participants were randomly assigned to receive either a single dose of 11 milligrams testosterone or a placebo, both administered through the nose, in a double-blind trial. After waiting 30 minutes for the hormone to take effect, the participants took part in a series of well-known decision-making games and tasks used in behavioral economics. These tasks measured things like risk taking, generosity, willingness to compete and fairness preferences.

The result showed no statistically significant effect of testosterone on any of the nine main outcomes. Men who received testosterone behaved, on average, the same as those who received the placebo.

"This study is significant because it directly challenges the narrative that short-term fluctuations in testosterone explain why some people take bigger economic risks, reject unfair deals, or act more competitively in life," says co-lead author Justin M. Carré, Professor at the Faculty of Arts and Science at Nipissing University in Canada.

That doesn't mean testosterone has no role in behavior. The researchers caution that their study tested only one dosage and timing in men. Different effects might also emerge under alternative dosages or during long-term hormone fluctuations. Also, women were not part of the trial, leaving open questions for future research.

"Our findings underscore the value of replication with larger samples and preregistered designs. Findings reported from small experiments can vanish when tested more rigorously," says co-lead author Magnus Johannesson, Professor at the Department of Economics at SSE.