The most pernicious of these problems is that women--yes, more than half the earth's population--are considered a high risk group because researchers fear menstrual cycles will affect test results. Until 1993 policy changes, excluding women from trials was the norm. Many trials have not been re-done to include women, and the policies don't include animal trials, so many rat studies, for example, still do not include female rats--a practice which makes later human trials more dangerous for (human) female participates.
[1] Sort of one citation: https://www.aamc.org/news/why-we-know-so-little-about-women-... There's more than this--I wrote a paper about this in college, but I don't have access to jstor now, so I'm not sure I could find the citations any more.