Male secum agit aeger, medicum qui heredem facit.
(Publilius Syrus, Sententia 626)

It goes badly for the sick man who makes the doctor the beneficiary of his will.

(pron = MAH-lay SAY-koom AH-git AI-gher, MEH-dih-koom kwee he-RAY-dem FAH-kit)

Comment: This proverb made me laugh out loud. Unfortunately the Romans did not
have a good experience with “medicine” or with doctors. Medical knowledge was
not very advanced. A good practicing wise woman (aka witch) might have served
you better with her knowledge of herbs than a Roman doctor.

Martial has an epigram in which he speaks of a man, now an undertaker, who used
to be a doctor. What he used to do as a doctor, he now finishes as an
undertaker.

So, the short of it? See the big picture, and avoid conflicts of interest!
Perhaps we should write this proverb on pieces of paper and send them to US
Pharmaceuticals!