Crossover Target Engagement Study of Cholinergic Mechanisms of Gait Dysfunction in Parkinson's Disease (Project #3 - Experiment 3 [UdallP3E3])

Initial 0.25 mg oral dose of varenicline administered with monitoring over 4 hours, then total daily dose escalated over the next 2 days until final 0.5 mg BID oral varenicline administered for the remaining 3 weeks.

Initial placebo oral dose administered with monitoring over 4 hours, then total daily dose escalated over the next 2 days until final placebo BID dosing administered orally for the remaining 3 weeks.