The investigators hypothesize that small intestinal (SI) microbiome biomarkers predict the responsiveness to oral levodopa/carbidopa in people with Parkinson's disease (PwPD). The investigators will analyze the bacterial species and function of bacterial pathways influencing the responsiveness of PwPD to oral L-dopa. The investigators will pursue this goal using a reliable capsule system (SIMBA capsule, Nimble Science, Calgary, AB) that suitably captures SI luminal fluid for multi-omics analysis.

Inclusion Criteria:

1. Males and females aged 50-85 years old at time of on-site visit. (ages 81-85 will be assessed on a per case basis by the principal investigator)
2. Signed Informed consent.
3. Willing & able to comply with study procedures (including SIMBA capsule ingestion) and have study assessments performed.
4. Able to swallow a size-00 capsule (25mm length) in OFF state.
5. Diagnosis of idiopathic PD (Clinically Probable PD), including documented levodopa responsiveness.
6. Treatment with an immediate release levodopa formulation during the day at a stable dose for at least 2 months prior to enrollment.

Exclusion Criteria:

1. Any risk of capsule non-excretion related to intercurrent gastrointestinal conditions.
2. Use of any medications in the week prior to the on-site study visit, unless part of regular treatment, that could substantially alter gastrointestinal motor function.
3. History of oropharyngeal dysphagia, or other swallowing disorder with a risk of capsule aspiration, e.g., SDQ score > 4.
4. Any concomitant or previous treatment (<2 months from on-site study visit) with significant anti-inflammatory or immune suppressant medication, e.g., DMARDs, biologicals or systemic corticosteroids, except non-chronic PRN use of an NSAID and/or 5-ASA (mesalazine) treatment.
5. Active cancer within 5 years.
6. Clinically significant immune deficiency (according to Investigator's judgement).
7. Antibiotic use (except for local use), ≤12 weeks prior to on-site study visit, or Fecal Microbiota Transplantation anytime in medical history.
8. Use of prebiotics, or probiotics ≤2 weeks prior to the on-site study visit.
9. Dementia in medical history.
10. Insulin-dependent diabetes mellitus.
11. Current Psychosis episode by clinical judgement based on anamnesis.
12. Pregnancy.
13. Alcohol or drug abuse.
14. Deep brain stimulation or Duodopa/Lecigon treatment.

Any patient with Parkinson disease fulfilling section criteria.