The purpose of this study is to evaluate the efficacy and safety of the study drug, IPN10200, and to assess how well it works when compared with placebo in treating Cervical Dystonia (CD) in adults. CD can cause a series of abnormalities and symptoms in the head and neck that can lead to neck pain and stiffness, and headaches. CD is believed to involve deep parts within the brain that control movement, but genetic factors, environmental factors, and abnormalities in the brain may also play a role. The usual treatment for CD includes injecting BoNT into the affected muscles, but the treatment only lasts about 3 months. IPN10200 is designed to last for a longer period. The study will consist of two periods: 1. A Screening Period of up to 4 weeks (28 days) to assess whether a participant can take part in the study and requires at least one visit. 2. A Treatment Period of 36 weeks. On Day 1 of the treatment period, participants will receive either IPN10200 Dose A or Dose B (additional participants may receive IPN10200 Dose C) of the study drug, or placebo distributed into different muscles in the head, neck and shoulders. Participants may continue some other medications, but details need to be recorded. There will be 10 visits to the clinic in person and one remote visits (phone call) (12 visits to the clinic for participants who receive Dose C). Participants will undergo blood samplings, urine collections, physical/neurological examinations, and clinical evaluations. Participants will also need to complete questionnaires throughout the study. The total study duration for a participant will be up to 40 weeks (approximately 9 months).