Current literature suggests that the gut microbiota is altered in patients with Parkinson's disease (PD) and might play a role in the clinical presentation and pathogenesis of this condition. The latter has driven the interest in investigating the use of gut microbiota-modulating interventions, such as probiotics, as possible novel therapeutic strategies for PD. Symprove is a food supplement working as an oral active probiotic which unlike many commercially available probiotics can reach the intestine and has been shown to be beneficial for gut health in gastrointestinal disorders.To date, no research has explored the possible effects of the intake of Symprove in PD. This is an exploratory study with a randomised, double-blind, placebo-controlled design investigating the effects of a 12-week probiotic intervention (Symprove) on gut and general health in 60 patients with PD and constipation.

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