Regardless, if adderall withdrawal made you feel suicidal then I'm glad you walked far away from it. Best of luck to your sister, too. I hope she's able to stay clean.
Weed, at least, seems fairly benign (never touched it, never plan to). I still have a hard time wrapping my head around the fact that it's illegal in most of the US while tobacco is legal.
And yeah, gotta love that ADD/ADHD diagnosis, huh? My best friend was diagnosed with "ADD" (a.k.a. being a kid) back in the day and was put on Ritalin. Strangely enough, putting a kid on stimulants only serves to make them worse. When he got taken off of Ritalin in 5th grade his behavior and demeanor improved immediately.
That's actually one of the reasons I only consume caffeine "recreationally" (i.e. 0-200mg per week, spread throughout). I used to ingest about 300-500mg daily and it left me unable to focus, unable to sleep, and extremely irritable. It's funny how much legal, non-Rx substances can affect you.