This study is exploring if ketamine, a medication, can help with depression in Veterans with Parkinson's Disease (PD). Parkinson's is a disease that affects the brain, making it hard to move and sometimes causing depression. Ketamine has shown quick benefits for depression in other cases and may help improve brain health and reduce inflammation (swelling in the body).

For the study, 80 Veterans will get either ketamine through an IV (a tube in the vein) or a placebo (a fake treatment) to see if it helps their depression. The study will also look at how ketamine affects brain changes and inflammation to see if it could be a useful treatment.

• Participation involves one dose of ketamine and several study visits.
• Participation requires being a Veteran with PD and having tried other depression treatments.
• Participants must agree to not use certain substances or change medications during the study.

Results from this study will guide future research, potentially helping Veterans with PD struggle less with depression.