My son has done the same thing for a long time — collecting and squirreling away stuff he finds on the floor or lying around. He doesn’t take things from stores, fortunately, and it has improved a great deal with age (he doesn’t fill his pockets with rocks and twigs and anything and everything around him anymore). I do agree that it feels more like a compulsion, but we’ve never evaluated for OCD and no doc/therapist has ever suggested it.
Interestingly, he has started describing his impulsive actions as not having any control over his brain in those moments and then feeling extremely remorseful after. That description does sound more like compulsion that impulsivity, maybe. Something to think more about…
Intuniv is often used with a stimulant to try to improve impulsivity more. I’ve heard on clonodine/Kapvay being used for this as well (they’re similar medications). Here’s more information and user reviews on both:
ADDitude Community Moderator, Author & Mentor on Parenting ADHD, Mom to teen w/ ADHD, LDs, and autism