ELI5: Why isn't body mass considered for recommended medicine doses?

The years of misdiagnosis is what gets me.

I know, I know, if you hear hoofbeats, think horses, not zebras. But it's a shame the zebra diseases get a lot more time to debilitate while the horses are investigated.

A lot of my issues point to something systemic, quite probably in the autonomic system. Fortunately, while my GP doesn't think there's anything cryptic (his word, not mine), he's willing to refer me out to specialists because he knows the limits of his practical area of practice (and he might be humoring me (I'm one of those patients who looks things up), but I like to think it's mainly the former). But even, say, going to a neurologist, they want to rule out something and send me to another specialist. Who confirms there's a problem there and the diagnostic process stops for the treatment process, and it's only when the treatment process fails that diagnostics can continue.

/r/explainlikeimfive Thread Parent