Why Don't Scientists Use Female Mice?

Recent studies show that female mice are rarely used in lab experiments, but what implication does this have on the results of drug testing?

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One of the major issues in the world of scientific research is the reliance on only male subjects-specifically mice. A huge percentage of studies involving mice have only used males for test subjects. In fact, in scientific studies that report which sex they use, male mice outnumbered female mice five to one. One meta-study looked at scientific research as a whole and found that, of 1,200 papers surveyed, only 42 disclosed the sex of their lab animals. In other words, the ratio of male to female test subjects could be even higher.

This had led to some major issues. Mice are often the test subjects for pharmaceuticals, before the drugs are offered to humans. In Scientific American, Brook Borel explains how Ambien was developed using only male test subjects. However, it turns out men and women metabolize the drug at different rates. Women were still feeling the effects of the drug more than 11 hours after taking it. Twenty-one years later, the FDA issued new guidelines for Ambien, with recommended dosages for men and women. Similar issues have arisen for a host of drugs, including aspirin.

The science community is trying to make changes, but it will take time. First and foremost, there are major costs to be considered. Including equal size samples of male and female subjects effectively doubles research costs-a big deterrent for researchers. Still, the industry is starting to make changes. Last year, the National Institute of Health began requiring all research grant proposals to use both sexes or justify why their study only needed one. Considering the NIH supports some 300,000 researchers, that's a pretty big deal.

Learn More:

Is NIH policy the best way to sex equality in studies? (Science News)
"In many scientific fields, the study of the body is the study of boys. In neuroscience, for example, studies in male rats, mice, monkeys and other mammals outnumber studies in females 5.5 to 1."

NIH to balance sex in cell and animal studies (Nature)
"The NIH plans to address the issue of sex and gender inclusion across biomedical research multi-dimensionally - through programme oversight, review and policy, as well as through collaboration with stakeholders including publishers."