Hot take... Bipolar Disorder (as well as its milder cousin Cyclothymia) is just a subtype of ADHD, not its own separate disease. It is essentially where a person with ADHD cycles through ADHD-I (Inattentive subtype) and ADHD-HI (Hyperactive/Impulsive subtype). Essentially the ADHD-I is mistaken for the depressive phase and ADHD-HI is mistaken for the manic phase.
The various evidence supporting this:
* There is medical evidence suggesting a close genetic overlap between the two diseases.
* There is a very strong comorbidity with 20% of people with ADHD also having some form of BD
* The symptoms of each type closely resemble the characteristics of each pole of BD, so they are easily mistaken for eachother.