This news story demonstrates that research methods are both federally monitored and that best practices can change over time.
For a long time, women were not used in large scale pharmaceutical trials. Why did they omit women? They didn't want to accidentally exposed pregnant women to new drugs and because of fears that fluctuations in females hormones over the course of a month would affect research results. Which always makes me think of this scene from Anchorman:
But I digress. This has been corrected for and female participants are being included in clinical trials. But many of the animal trials that occur prior to human trials still use mostly male animals. And, again, policies have changed to correct for this. This NPR story details the whole history of this sex bias in research. Part of why this bias has been so detrimental to women is because women report more side effects to drugs than do men. So, by catching such gender differences earlier with animal models, there is the hope that fewer drugs will be developed that could hurt women. Additionally, such research has already uncovered sex differences that could benefit women and lead to new medical treatments for women. One study found that the way in which pain is communicated at the cellular differs between men and women (which may change how we treat pain in men and women). Another study may have uncovered a novel way to treat MS symptoms after finding that pregnancy hormones reduce MS symptoms.