NIH policy: Mandate goes too far

The planned mandate of the US National Institutes of Health (NIH) to include both sexes in effectively all preclinical studies could undermine its own objective by wasting resources, slowing down research or even provoking a backlash (see J. A. Clayton and F. S. Collins Nature 509, 282–283; 2014). Instead of a blanket mandate, the NIH should be promoting research into the sex differences that are important to science and in disease.

Duplicating studies to “compare and contrast experimental findings in male and female animals and cells” is rarely practical, affordable, prudent, scientifically warranted or ethically justifiable. Researchers use both sexes because this roughly halves the costs of breeding and maintenance. Sometimes one sex is excluded if results are likely to differ between sexes, and possibly for well-known reasons — for instance, male rats run faster than female rats through a maze. If there is no justification for studying both sexes, then it should not be done.