SIBO and Parkinson's Disease: Prevalence, Motor Symptoms and Treatment

In short: SIBO is common in Parkinson’s disease. A 2021 meta-analysis of 11 studies found it in 46% of people with Parkinson’s, with about five times the odds of healthy controls¹. The most likely reason is that Parkinson’s slows the whole digestive tract². Several studies link SIBO to worse motor symptoms³⁴, and one linked it to more unpredictable responses to medication⁵, and one small study found that clearing SIBO improved motor fluctuations⁵. No large randomized trial has tested SIBO treatment in Parkinson’s.

Why Parkinson’s and SIBO are linked

Parkinson’s affects the digestive tract from top to bottom. Problems range from drooling and difficulty swallowing to delayed stomach emptying and constipation². The protein that builds up in the brain in Parkinson’s, alpha-synuclein, is also found throughout the nerves of the gut². Slower movement through the gut is present early in most people with Parkinson’s and is thought to set the stage for SIBO⁶, in the same way that slow motility causes SIBO in other conditions; see what causes SIBO and motility and the migrating motor complex.

Whether SIBO, in turn, affects how Parkinson’s progresses is an open research question. A 2021 review discusses the possibility but notes that the role of gut bacteria in causing or worsening Parkinson’s is not yet understood⁶.

How common is SIBO in Parkinson’s?

The rate depended on the test and the region. In the meta-analysis, it was 51% in studies using the lactuloseLactulose A synthetic sugar the body cannot digest or absorb. As a breath-test substrate it travels the whole small intestine, which also makes false positives more likely. breath test and 35% with the glucose breath test, and 52% in Western countries compared with 33% in Eastern countries. The results varied widely between studies¹. See breath tests explained for why the two tests differ.

SIBO and motor symptoms

• In the 2011 study, SIBO was more likely in people with more advanced Parkinson’s, as measured by standard disease stage and rating scales³.
• In the 2014 study of 103 people, in which both patients and assessors were unaware of SIBO results, SIBO was linked to worse motor scores while on medication, after allowing for how long people had had Parkinson’s. SIBO explained only 4% to 9% of the differences in motor scores. Surprisingly, people with SIBO had less severe constipation, and SIBO was not linked to motor fluctuations or quality of life⁴.
• In the 2013 study, people with SIBO had more “off” time each day and more episodes where a levodopa dose took effect late or not at all⁵.

A 2015 review suggests that SIBO and H. pylori infection may cause motor fluctuations by interfering with how Parkinson’s medicines are absorbed². In the 2013 study, unpredictable fluctuations were found in 87.5% of people with both SIBO and H. pylori, compared with 8.3% of those with neither⁵. See H. pylori and SIBO.

Does treating SIBO help?

The only treatment results we found come from the 2013 study. People with SIBO were treated with the antibiotic rifaximinRifaximin An antibiotic that is barely absorbed into the bloodstream, so it acts mainly inside the gut. It is a common prescription treatment for SIBO. and followed for 6 months. Clearing SIBO improved motor fluctuations, but it did not change levodopa levels in the blood, so better absorption does not seem to explain the benefit. SIBO came back in 43% within 6 months⁵.

This was a small study without a placebo group. A 2021 review notes that SIBO can be cleared with antibiotics but tends to return if the condition behind it persists, which in Parkinson’s it does⁶. Repeated treatment and support for gut movement may therefore be needed; see preventing SIBO relapse and our antibiotics guide.

What this means if you have Parkinson’s

• Mention digestive symptoms to your neurologist. Bloating, gas, diarrhea or weight loss are worth raising, and so are levodopa doses that seem to work less reliably.
• Testing is an option, not routine. We found no guideline that recommends testing everyone with Parkinson’s for SIBO.
• Review other risk factors. Acid-suppressing medicines and other conditions can add to the risk; see what causes SIBO.

Common questions

Does SIBO cause Parkinson’s?

We found no evidence that it does. Reviews suggest that the slower gut movement of Parkinson’s makes SIBO more likely, and whether SIBO then affects the course of the disease is still being studied⁶.

Can SIBO affect levodopa?

It has been linked to delayed or failed responses to levodopa doses and to more “off” time⁵. In the 2013 study, however, treating SIBO improved fluctuations without changing levodopa blood levels⁵.

Is constipation in Parkinson’s a sign of SIBO?

Not necessarily. Constipation is a common part of Parkinson’s itself², and in the 2014 study, people with SIBO actually had less severe constipation⁴. Methane-type overgrowth is the form most linked to constipation; see methane SIBO.