The natural sex hormone progesterone first used in contraceptive pills and naturally extracted from yams seems likely to reduce swelling and repair neurons in patients with severe head trauma. "Scientists will begin a phase III clinical trial in March and say the drug could save patients' lives and reduce damage to their brains. They announced the trial at the annual meeting of the American Association for the Advancement of Science. It will involve 1,000 patients in 17 trauma centres across the US. Dr David Wright, associate professor of emergency medicine at Emory University in Atlanta, will lead the trial.Previous studies have shown that progesterone supports the normal development of neurons in the brain, and that the hormone has a protective effect on damaged brain tissue. Dr Wright told BBC News: 'Traumatic brain injury is a complex condition - there's swelling, and neuronal death and damage occurring all at the same time. The beauty of progesterone is that it seems to work on all of those things.'"