The trial design will consist of a randomized, double blind, placebo-controlled 2 parallel arm study. The two randomly assigned treatment groups will consist of administrating a placebo or short-acting MPH two-times daily 1 hour before meals for a period of 2 months (60 consecutive days). Prior to being randomized into either the placebo group or the experimental (MPH) group, subjects will first have had to respond to a recruitment poster, newspaper advertisement. Once it is determined with that initial screening that the participant still meets inclusion criteria, they will be invited to come to the laboratory for a screening visit to determine whether they meet eligibility criteria, to sign informed consent, and to take a test dose of MPH in order for a nurse to closely monitor any potential side-effects prior to starting the 2-times daily dosing of MPH or placebo.