If you say "specializing in ADHD", you are not saying anything about certification. If you say "certified in ..." you would be.
I also have experienced a number of docs who are trained in one area but either doing a subcategory or in a somewhat different field. What counts is experience and comfort and familiarity with the field, all of which I have little doubt you have in ADHD.

Wendell
Pediatrician in Chicago

The patient's expectation is that you have all the answers, sometimes they just don't like the answer you have for them