I am proud to be a Functional Medicine (FM) Doctor just like I am proud to be a Naturopathic Doctor (ND) . Understand that these titles have meaning. There are other doctors who have taken an online or in person weekend seminar and who advertise themselves as practicing functional medicine.
I can tell you that as someone who supervises a doctor residency program in functional medicine as well as someone who has helped facilitate study groups for MD's trying to correctly practice FM that a weekend seminar does not a doctor make. I still take recertification through the Institute of Functional Medicine (which is the first and only professional training group teaching functional medicine IMO) even though I am fully qualified. Why? Because there is always something to learn and some new research to be applied for my patients. I can assure you that I will never stop at one or 2 weekend seminars where my patients health is concerned.
To learn more about Functional Medicine and the Institute of Functional Medicine please check out the link for a short (lol) article describing what it is and isn't