Larry Cahill, professor of neurobiology and behavior at the University of California at Irvine, reports that 90 percent of U.S. medical research conducted on mice or rats is done with male rodents. Speaking at a neurobiology conference in Toronto, Dr. Cahill stated male rodents are used for research even on diseases that disproportionately affect women. For example, women make up 70 percent of the patients that suffer from chronic pain. But in the 1996-2005 period, 80 percent of the studies involving research with rodents, that were published in the journal Pain, used only male rats and mice.
Many researchers believe estrogen levels in female mice will skew their results, according to Dr. Cahill.