PBT434 inhibits alpha- synuclein in the brain., page-27

That cocaine paper clearly states they think disregulation of iron homeostasis is a strong possibility as the cause of the associated PD.
[Stimulant drugs acutely increase dopamine neurotransmission in the brain, and chronic use leads to neuroadaptive changes in the mesolimbic dopamine system and morphological changes in basal ganglia structures. Little is known about the mechanisms underlying these changes but preclinical evidence suggests that iron, a coenzyme in dopamine synthesis and storage, may be a candidate mediator. Iron is present in high concentrations in the basal ganglia and stimulant drugs may interfere with iron homeostasis. ]
https://www.nature.com/articles/tp2016271
Very interesting considering PBT434 is a great drug to re-establish iron homeostasis.
I think alcohol addiction could have a similar outcome. A good friend has recently given up his alcohol consumption and had a Parkinson's tremor for a week till his system adjusted to the absence of alcohol.