This is a double blinded randomised placebo controlled trial to evaluate the efficacy of probiotics in the treatment of constipation in Parkinson's disease.

Inclusion Criteria:

• Age 50 to 80 years old
• Provision of written informed consent
• Diagnosis of PD made by a Neurologist using UK Brain Bank Criteria
• Fulfils criteria for functional constipation according to the Rome IV Criteria during in the preceding 6 months with frequency of bowel movements less than 3 times per week

Exclusion Criteria:

• Ingestion of probiotics in the preceding 4 weeks
• Use of antibiotics in the preceding 4 weeks
• History of gastrointestinal disorders or surgery
• Known or suspected allergy to probiotics
• Comorbidities that prevent reliable completion of study assessments
• Prior functional neurosurgery for PD or treatment with apomorphine infusion
• Recent initiation of dopaminergic medications in the preceding 3 months

Double blinded