This study is testing a new medicine called **VIM0423** for people with *isolated dystonia*. Dystonia is a condition where muscles contract and cause unusual movements or positions. This study compares VIM0423 to a placebo (a pill with no medicine) to see if it helps improve symptoms and daily life quality. **Key Points:** - Participation involves taking up to 6 pills daily for 16 weeks, and the entire study lasts up to 32 weeks with 6 in-person visits. - Participants will undergo various tests, including video recordings, clinical labs, and heart tests (EKGs) to monitor safety. - You need to be 18-65 years old, have had dystonia for at least one year, and have it in two or more body parts to join. VIM0423 is an oral medication aiming to fix chemical imbalances in the brain that cause dystonia. Currently, only certain botulinum toxin (BoNT) injections are approved in the U.S. for dystonia, but they only treat specific types. This study seeks to offer a broader treatment option for those affected.