[hirvi74]

> has anyone here gotten diagnosed and medicated in adulthood

Yes.

> and found it made a meaningful difference specifically for self-directed, long-term projects?

No.

I was dx'd in my early twenties and have been treated for over a decade. I would say there is a minor improvement in some areas, but it's not like I became some radically different person. I'm still highly dysfunctional in a lot of domains.

I would say medication provides me a better ability to focus on tasks, but that is about it. Of course, if you start medication, you will likely become a radically different person during the 'honeymoon phase', but if you are like me, there will be a reversion to the mean.