for people ages 30 years and up (full criteria)
at San Francisco, California
study started
completion around
Principal Investigator
by Caroline Tanner



The clinical phenotype of Parkinson's disease (PD) is quite variable, as is the response to and side effects from medications. While many patients respond to carbidopa/levodopa early on, motor fluctuations and dyskinesias can become a problem as the condition progresses, causing significant impairment in function and quality of life. The gut microbiome is of increasing interest in PD, potentially contributing to pathophysiology and clinical phenotype. Furthermore, gut bacteria are capable of metabolizing levodopa, which may decrease its ability to reach the central nervous system and could explain the variable effect seen clinically. Altering the population of drug-metabolizing bacteria could improve the clinical symptoms of PD and the benefit seen with medications. The investigators hypothesize that the gut microbiome in people with PD correlates with their phenotypic characteristics, which can be improved with targeting the microbiome through dietary or therapeutic interventions. The investigators propose a two-part clinical trial. First, a cross-sectional analysis will correlate the microbiome profile with (a) the clinical phenotype of PD and (b) medication response. Second, a randomized, controlled trial, will evaluate the effect of microbiome manipulation on clinical phenotype and medication response. The investigators plan to reduce the level of bacteria through antibiotic use, resetting the potentially disadvantageous microbiome population. Outcomes will include changes in clinical symptoms, alterations in the the microbiome, and changes in serum markers of inflammation. This thorough characterization will broaden our understanding of the gut-brain axis significantly in PD in clinically relevant ways that have yet to be explored.


Parkinson Disease, Rifaximin


You can join if…

Open to people ages 30 years and up

  • Parkinson's disease
  • Stable on levodopa therapy with fluctuations

You CAN'T join if...

  • Chronic gastrointestinal disease
  • Recent antibiotic or probiotic therapy
  • Pregnant
  • Immunocompromised


  • UCSF accepting new patients
    San Francisco California 94115 United States

Lead Scientist at UCSF

  • Caroline Tanner
    Professor, Neurology, School of Medicine. Authored (or co-authored) 216 research publications


accepting new patients
Start Date
Completion Date
University of California, San Francisco
Phase 1/2 Parkinson's Disease Research Study
Study Type
Expecting 86 study participants
Last Updated