This article talks about a study of the effects of testosterone and cortisol on stock trader behavior. An excerpt:

But which is the cause and which is the effect? A further analysis showed that traders who started their days with elevated testosterone made more money than those who didn’t. One trader went on a six-day winning streak, making twice as much money each day as the previous one. Over that period, his testosterone levels rose steadily, some 74 per cent.

“The popular view is that experienced traders can control their emotions,” Coates says, “but in fact their endocrine systems are on fire.”

There is a point of diminishing returns; too much testosterone leads to too much aggression and reckless decision making.

And while elevated cortisol levels probably contribute to better risk management in volatile situations, neuroendocrinologist Bruce McEwen of Rockefeller University, New York, says long-term elevation can ravage the body with anything from cardiovascular disease to arthritis.