I do not in the least intend this to be challenging but as far as I can see "functional medicine" is just one of the many and mutually exclusive versions of comp/alt med.

I confess that my BS detector quivers when a health practitioner uses a question-begging term like "functional medicine" to describe their approach.

A question for you to ponder:

Do you know of any health practitioners who advocate "dysfunctional medicine" or "non-functional medicine"?

Caveat emptor.