Inclusion Criteria:  Completed an Addex randomized controlled study of dipraglurant and, in the judgement of the Investigator, may benefit from open-label treatment Able to take study drug 3 times daily and no less than 3 hours apart Must be taking levodopa not less than 3 times daily throughout the study Must maintain stable regimen of antiparkinson's medications (including levodopa) and be willing to continue the same doses and regimens for the first 4 weeks of the study  Exclusion Criteria:  Patient is judged by the Investigator to be inappropriate for the study (for reasons such as, but not limited to, significant noncompliance in the Addex randomized controlled study of dipraglurant) Use of amantadine or amantadine ER throughout the study Use of memantine throughout the study Any use of marijuana or other cannabis/cannabinoid products for the first 4 weeks of study participation  Other protocol-defined inclusion and exclusion criteria may apply