A Study of TAK-071 in People With Parkinson Disease

It is hoped that TAK-071 will help people with Parkinson's disease to walk with better balance. The main aim of the study is to check if there is a difference in how participants walk after treatment with TAK-071. Another aim is to see if it improves how participants think and remember. At the first visit, the study doctor will check who can take part. Participants who can take part will be picked for 1 of 2 groups by chance. Both groups will have 2 treatments but in a different order. The treatments are TAK-071 tablets or placebo. In this study, a placebo will look like the TAK-071 but will not have any medicine in it. One group will take TAK-071 for 6 weeks, have at least a 3-week break, then take a placebo for 6 weeks. The other group will take a placebo for 6 weeks, have at least a 3-week break, then take TAK-071 for 6 weeks. The participants will not know the order of their 2 treatments, nor will their study doctors. This is to help make sure the results are more reliable. The participants will visit the clinic at the beginning and end of each treatment for a check-up. 14 days after the 2nd treatment, clinic staff will telephone the participants for a final check-up.

The drug being tested in this study is TAK-071. TAK-071 is being tested to treat people with PD who have cognitive impairment and are at risk for falls and who are not concurrently taking acetylcholinesterase inhibitors. The study will look at the efficacy and safety of TAK-071 in participants with PD who take TAK-071 versus placebo. The study will also evaluate the PK of TAK-071 in healthy participants (sentinel cohort) older than 55 years. The study will enroll approximately 74 participants. An initial sentinel cohort of 10 healthy participants will be included to estimate age effects. Participants aged 56 to 75 years will be randomly assigned in 3:1 ratio to one of the two treatments: * Sentinel Cohort: TAK-071 7.5 mg * Sentinel Cohort: Placebo Enrolment for participants aged 40 to ≤ 85 years in the main study will start simultaneously with sentinel cohort. Based on PK, safety, and physiologically based PK modelling data from sentinel cohort, dosing will be decided for the remaining participants. Participants with maximum age of 66 to 85 years, inclusive, will be enrolled at a dose of 5 mg, and the dose for subjects aged 40 to 65 years, inclusive, will be 7.5 mg. All participants will be asked to take one tablet at the same time each day throughout the study. The remaining participants aged 40 years to \<=85 years will be randomly assigned in 1:1 ratio to one of two treatment sequences in crossover design: * TAK-071 + Placebo * Placebo + TAK-071 The study will be conducted in the United States. The minimum time to participate in this study is approximately 15 weeks. Participants will make multiple visits to the clinic and will have home assessments during the third Week of each 6-week treatment period, and will be contacted by telephone at 14 days after completion of the last period for a follow-up assessment.