Study to Assess How ABBV-951 is Absorbed When Administered at Different Subcutaneous Sites of Adult Participants With Parkinson's Disease

Parkinson's disease (PD) is a neurological condition, which means it affects the brain. This study will evaluate how ABBV-951 is absorbed under the skin of participants with PD when administered to arm, thigh and flank compared to the abdomen. ABBV-951 is an investigational drug being developed for the treatment of PD. Study doctors randomly assign participants to 1 of 4 groups, called treatment arms. Each treatment arm receives ABBV-951 administered in a different order in the arm, high, flank and abdomen. Approximately 12 adult participants over 30 years with a diagnosis of PD will be enrolled in approximately 10 sites in the United States. Participants will receive continuous (24hours/day) subcutaneous infusion of ABBV-951 for 2 consecutive days for each infusion site (arm, thigh, flank and abdomen), for a total duration of treatment up to 12 days. There may be higher treatment burden for participants in this trial compared to their standard of care. Participants will be confined at a hospital or clinic. The effect of the treatment will be checked by medical assessments, blood tests, checking for side effects and completing questionnaires. Adverse events will be monitored throughout the study.