Was looking into the topic of "I am literally on a meth analogue why is it just calming me" (as does actual meth).
So here's my theory after some looking, continues on from some rants i've had before about this stuff trying to look into it. There's evidence to believe ADHD and BPD atleast in the impulsivity is typically coming from the same kind of neural dysfunction, the applicable area here being dysfunction in dopamine system. And if I understand correctly then other factors would influence how this is expressed, the BPD impulsivity vs the ADHD impulsivity that is. I can also say from personal experience with various forms of meds, including particularly bad reactions to most antipsychs, and some overlap in symptoms with bipolar enough to warrant discussion with therapists and pyschiatrists, that, well, this also kinda aligns with the dopamine dyfunction theory here. That's what I believe I have and what is probably causing the BPD and some other related and/or overlapping issues, and of COURSE the severe motivation issues I always seem to be having.
So, that's what I've settled on as a working theory, that I have dopamine dysfunction where it's affecting me in the similar way to ADHD here, atleast in calming. I don't like the other albeit rather mild effects it has on me, like I wouldn't take an amphetamine medically but it explains it's odd affect.
I should add there was also a study here finding that BPD subjects responded well to amphetamine as opposed to the control group and it didn't affect a growth hormone response as it normally would, suggesting, "Thus, borderline patients appear to be pharmacodynamically separable from normals.", where the BPD reported improvement under it.

I can't be arsed to pull out specific citations at the moment but here's a few the papers I looked at, alongside a lot of referencing other sources just to see if I was remembering shit and how shit works correctly:
"Emotion dysregulation in attention-deficit/hyperactivity disorder and borderline personality disorder", https://bpded.biomedcentral.com/articles/10.1186/s40479-018-0086-8
"Dopamine Dysfunction in Borderline Personality Disorder: A Hypothesis", https://www.nature.com/articles/1300424
"Amphetamine response in borderline patients", https://www.sciencedirect.com/science/article/abs/pii/0165178185900459