There is no good ELI5 here I think. First of all we recognized this only recently because there is a male centric bias in medicine. I’m of the opinion it is mostly due to historical reasons, and not nefarious.
But if I had to wave my hands I would say it is because of physiological difference and occupying different space in the society in the west. It likely has to do with development, heart strain from exercise and difference in perceptions of pain, but this is hardly a good explanation.
Women react to medications differently as well. Hence the need for them to be represented in medical trials.
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