We investigated whether restricting individuals with an ADHD history to those known to be prescribed methylphenidate and mixed-AMPH salts altered our observations. Regardless of model, a consistent pattern of significantly increased risk of BG&C diseases in this subset of stimulant-treated patients was detected. Possible explanations include: (1) treatment with psychostimulants may enhance the mechanism(s) responsible for the linkage between earlier-onset ADHD and BG&C diseases expression, (2) a history of ADHD with psychostimulant use may accelerate the temporal related degeneration of the relevant neuronal pathways primarily in those patients who eventually, with age, will manifest this disorder regardless of an ADHD history, or (3) psychostimulant treatment is a marker for a more severe ADHD phenotype, which in turn increases the risk of earlier BG&C diseases expression. Due to a general lack of evidence in either animals [46, 47] or humans [48] that methylphenidate per se damages nigrostriatal dopaminergic neurons, the latter explanation may be the most plausible (however see also ref. [49]).