Over 30 years ago a severe reaction to some medication for peritonitis had my doctors hurrying around because it damaged my liver.
The surgeon told me then that before I take anything ever again, to have my CBC & especially my liver enzymes tested, and then tested within a week after taking it, and then regularly every in 2-4 weeks while taking it for the first couple of months.

Can't tell you how often I have refused medications because the attending physician refuses to order this testing. If I am giving consideration to taking a medication, I request the repeating lab requisition before the MD writes the script.

Since spring of this year, I have basically been 'excused' from the care of my current MS neuro specialist because of me making this a requirement of trying an off lable use of a medication that he is doing a study on.
I got the sense that his main concern was that if it was found to have an adverse effect on what he calls 'atypical liver hypersensitivity", that it might have messed up his over-all test results.

It is possible that some drug companies & MDs don't mention possible side effects of meds for similar reasons.

With love, Erika