The aim of this clinical trial is to assess the impact of fecal microbiota transplantation (FMT) delivered via oral capsules in patients with Parkinson's disease who suffer from refractory constipation. The primary questions this trial seeks to answer are:

Does FMT delivered through oral capsules improve constipation? Does FMT delivered through oral capsules enhance the motor symptoms associated with Parkinson's disease? Is FMT delivered through oral capsules safe for individuals with Parkinson's disease? Researchers will compare the intervention group with a control group to determine the presence of a placebo effect.

Participants in the study will:

Take antibiotics as a pre-treatment regimen for 5 days, followed by oral capsules containing either fecal microbiota or a placebo for 14 days.

Attend clinic visits at screening, visit 1 (baseline), visit 2 (4 weeks), and visit 3 (12 weeks).

Collect fecal samples and maintain a 2-week diary of their bowel habits before visits 1, 2, and 3.

Inclusion Criteria:

• Aged between 40 and 80 years.
• Voluntarily signed the informed consent form for participation in this study.
• Diagnosed with Parkinson's disease according to the UK Brain Bank Criteria.
• Either do not have or have controlled Parkinson's disease motor complications, allowing for stable use of anti-Parkinson's medication during the study period (12 weeks).
• Meet the definition of refractory constipation as follows:

A. On at least 1 out of 4 bowel movements, two or more of the following apply: i. Excessive straining.

ii. Lumpy/hard stools (Bristol Stool Form Scale 1-2). iii. Sensation of incomplete evacuation after defecation. iv. Sensation of anorectal obstruction or blockage. v. Manual maneuvers to facilitate defecation. vi. Fewer than three spontaneous bowel movements per week. B. Rarely experience loose stools without the use of laxatives. C. Symptoms began at least 6 months prior to diagnosis and have persisted for the past 3 months.

D. Constipation shows no improvement despite the use of various types of laxatives (bulk-forming, osmotic, saline, stimulant, or others) individually or in combination for at least 4 weeks.

Exclusion Criteria:

• Individuals with cognitive impairment scoring less than 20 on the Korean version of the Mini-Mental State Examination (K-MMSE).
• Individuals who have contraindications for fecal microbiota transplantation (acute infections, immunocompromised status, or a history of food allergies).
• Individuals with ileus or colonic pseudo-obstruction.
• Individuals with a history of major gastrointestinal surgeries, such as resection.
• Individuals with suspected or confirmed gastrointestinal obstruction or gastric outlet obstruction.
• Individuals with suspected or confirmed active gastrointestinal bleeding.
• Individuals with gastrointestinal diseases requiring treatment or medical consultation.
• Individuals receiving parenteral nutrition or enteral feeding.
• Individuals experiencing dysphagia symptoms (difficulty swallowing, choking during meals, etc.).
• Individuals who have taken antibiotics within 3 months prior to screening.
• Individuals who have participated in other drug clinical trials within 3 months prior to screening.
• Pregnant individuals.
• Individuals with other severe diseases that may impair quality of life or the ability to perform daily activities.
• Individuals with contraindications to the use of antibiotics (Ciprofloxacin, Metronidazole) as referenced in the text.
• Any other case where the researcher deems participation in the clinical trial to be inappropriate for the subject.

Block randomization is performed by an unblinded Clinical Research Associate (CRA), assigning participants to either the treatment group or the placebo group in a 1:1 ratio. All other researchers involved in the study remain blinded to group assignments. The researcher responsible for randomization does not engage in any other aspects of the research process. Randomization records are maintained separately from other clinical data to ensure confidentiality. Researchers, aside from the one handling randomization, are unaware of which participants are in the treatment or placebo group.