Gut Health and Probiotics in Parkinson's (SymPD)

Inclusion Criteria: * Age of 18 and upwards * Diagnosis of idiopathic Parkinson's disease according to the Movement Disorder Society clinical diagnostic criteria * Hoehn Yarh stage II-IV * Diagnosis of constipation according to the ROME IV criteria and ≤ than 3 complete bowel movements per week Exclusion Criteria: * Diagnosis or suspicion of other causes for parkinsonism * Advanced-stage therapies (deep brain stimulation, intrajejunal levodopa infusion, and apomorphine subcutaneous infusion) * Any inflammatory bowel disease or diseases of the colon * Previous surgery on the gastrointestinal tract * History of laxative abuse * Ongoing artificial nutrition * Regular use of probiotics * Previous intolerance and/or adverse reactions to probiotics * Previous use of Symprove * Recent or current use of any antibiotics (within 4 weeks before the start of the study) * Swallowing issues interfering with the safety intake of the probiotic/placebo * Pregnancy or lactation * Major systemic disease * Any condition interfering with the ability to give the informed consent * Enrolment in another simultaneous investigational trial