Were there examples of effective medical treatments that Humoral Theory accidentally got right?
For well over 1000 years most western medicine was based on this notion that health was a function of balance within the four humors. Obviously the whole thing has been debunked in the modern age, but do we know of things that pre-modern doctors were doing that modern medicine would recognize as being likely to produce a good result despite the basis being incorrect.
One example I had heard of was that in some effort to balance either the hot/cold or wet/dry aspect of a person's humors there was a treatment to boil a horseshoe in wine then drink the wine. The premise was false, but the effect would have been to partially help correct an iron deficiency which has actual medical value in some cases.