This study will examine the effects of lithium 20mg/day compared to placebo on MRI and blood-based biomarkers among 20 early-stage Parkinson's disease patients.

In observational studies, small daily doses of lithium have been associated with a 77% reduced risk of developing Parkinson's disease (PD). In addition, lithium therapy has been effective in preventing neuronal death and behavioral symptoms in several PD animal models. Recently, our group has shown 24-weeks of low-dose lithium therapy in PD to improve both MRI and blood-based biomarkers implying that lithium may be slowing the progression of the disease. However, these findings stem from only three of four patients receiving MRIs. A larger study will be required to determine if these promising results can be replicated. The proposed study will enroll 20 additional PD patients who will be randomly assigned to receive either lithium 20mg/day or identically-appearing placebo capsules for 24 weeks. This will be a double-blind study meaning that neither the patients nor the study team will know to which therapy patients have been assigned. Positive results from this study will support further research on lithium that could eventually support lithium as a disease-modifying therapy for PD that could improve patients' long-term prognoses.

Inclusion Criteria:

• Have PD for <4 years diagnosed by a movement disorder specialist. Have normal thyroid and renal function at the screening visit. Have no previous exposure to lithium therapy. Have no history of brain surgery. Have no hx of brain imaging findings suggesting another neurological condition besides PD.

Have no use of tobacco or THC products for >1 year. Have stable PD medications for >30 days without current need for adjustments in the investigator's opinion.

Have stable psychiatric and diuretic medications for >60 days with no anticipated need for changes for at least 24 weeks.

Have no active medical or psychiatric condition that may interfere with study procedures in the investigator's opinion.

Exclusion Criteria:

• Have PD for >4 years or does not have PD. Have abnormal normal thyroid and renal function at the screening visit. Have previous exposure to lithium therapy. Have history of brain surgery. Have hx of brain imaging findings suggesting another neurological condition besides PD.

Have use of tobacco or THC products within the past year. Have PD medication adjustments within 30 days or needs PD medication adjustments in the investigator's opinion.

Have psychiatric or diuretic medication adjustments within the last 60 days or is anticipated to need changes over next 24 weeks.

Have active medical or psychiatric condition that may interfere with study procedures in the investigator's opinion.

IPD will be considered on a case-by-case basis.