I think tribal and political social media discourse has exacerbated this effect, by which I mean, blanket acceptance of the ADHD diagnosis process and medication is now left-coded.
Conspiracy theorist anti-vax types exhibit "Big Pharma" skepticism, so media and pundits take great care to remind people of this. They want them to believe that they're picking a side in tribal politics.
edit: Another way it becomes left-coded is exhibited in this thread: victimization and grievance politics.