Nearly everything on the ADHD list can show up inside a bipolar presentation, and the reverse is not true. So the shared features settle nothing, and the distinctly manic ones carry all the weight.

What the research says

A review of adults who came to services for another psychiatric problem found ADHD sitting unrecognised underneath surprisingly often, partly because the symptoms overlap with other diagnoses and partly because people are not always good witnesses to their own attention. It is a narrative review rather than a study of diagnostic accuracy, so read it as clinical argument. The overlap it describes is precisely what makes the shared features such weak evidence.

Strength of evidence: one line of research. A single study, or a theoretical account.