Except you treat depression and anxiety by increasing the availability of serotonin in the synaptic gap (reuptake inhibition), while ADHD can be treated with atomoxetine which inhibits noradrenaline reuptake thus influencing the availability of dopamine. And while it’s true that atomoxetine can be used both in ADHD treatment as well as anxiety, methylphenidate and lisdexamfetamine dimesylate is used as well for ADHD, especially if the symptoms are indicative of strong attention deficit relative to the hyperkinetic symptoms.

So it’s not just a matter of treating the symptoms in this case, and you need to understand the root cause to treat effectively. A person with a strong serving ADD in their ADHD, such as yours truly, can present as depressed, but SSRI did nothing more than remove my moods, both positive and negative, rendering me an emotional zombie.