This time both stories are about the gut. One looks at how the gut bacteria of people with Parkinson’s shift with age, disease stage and the medications they are taking. The other finds that a drug given specifically to make levodopa work better can reshape those same bacteria in a way that cuts into the benefit instead. We’ve put them together because between them they show why the gut keeps coming up in Parkinson’s research, and how it connects to how well medication works.
The makeup of gut bacteria shifted with age, disease stage and medication
🔍 How this came about
Researchers in southern China analysed the bacteria in stool samples from 42 people with Parkinson’s (average age 64.1) and 25 age-matched controls, publishing the results in the journal Antonie van Leeuwenhoek. The makeup of gut bacteria was clearly different between the two groups — Ruminococcaceae, Clostridiales and Alistipes were more abundant in the Parkinson’s group, while Bacteroides and Lachnospiraceae were more abundant in the control group.
What stands out is that this difference did not show up the same way at every age. Below 60 there was almost no difference between the two groups, and it only became clear from 60 onwards. Certain bacteria were also more abundant at higher disease stages, and the makeup differed again depending on whether someone was taking an anticholinergic or a dopamine agonistA medication that acts in the brain much like dopamine does. It is used on its own or alongside levodopa, and is known to carry a clearly higher risk of impulse control disorders than levodopa.Learn more.
✅ For you
The fact that gut symptoms such as constipation are common in Parkinson’s and the fact that gut bacteria keep coming up in the research are connected. The idea that changes starting in the gut can carry through to the brain has been studied for a long time — the Braak hypothesisA hypothesis that in some people alpha-synuclein starts clumping in the gut or the olfactory nerve before it does in the brain, then slowly travels up to the brain along the vagus nerve.Learn more is the best-known version of it. This study adds that those gut bacteria also move in step with disease stage and with the medications being taken.
🙋 For your care partner
Hearing something along the lines of “gut bacteria are the cause” sometimes leads families to start buying probiotic products. On the evidence available so far, no product can be said to slow the progression of Parkinson’s. Constipation itself, though, affects both quality of life and how well medication is absorbed — so if constipation is there, raising it at the next appointment is far more useful.
A drug meant to boost levodopa may, through gut bacteria, cut into it instead
🔍 How this came about
Researchers at Yale School of Medicine in the US published this study in the journal Nature Microbiology. Their subject was the COMT inhibitorAn add-on medication that stops levodopa from being broken down in the body, so more of it reaches the brain. Entacapone and opicapone are the common ones, and it is often dispensed as a single combined tablet with levodopa.Learn more — a drug taken alongside levodopa to make it work better, by stopping levodopa from being broken down too quickly in the body.
What caught the researchers’ attention is that these drugs also act as antibiotics. A COMT inhibitor kills off some bacteria in the gut, while the bacteria that can tolerate it multiply instead. The problem is that Enterococcus faecalis (E. faecalis) is among the survivors that multiply — this bacterium carries an enzyme that breaks levodopa down, so it uses the drug up in the gut before it ever reaches the brain. Sure enough, the more of this bacterium a person carried, the less benefit they tended to get from levodopa.
Dr. Andrew Verdegaal, who led the research, described it as finding the opposite effect from a drug taken specifically to raise the benefit of levodopa. The team also singled out what they see as the wider point — drug interactions are usually assumed to happen in the liver, but this one happens through the microbes in the gut.
✅ For you
This is a clue that could help explain why the same drug at the same dose works differently from person to person. What it is not is a reason to cut down or stop anything on your own — a COMT inhibitor is prescribed to slow the shortening of how long each dose lasts, and plenty of people genuinely benefit from it.
🙋 For your care partner
Deciding whether to change a medication is the care team’s call, but the raw material for that decision can only be gathered at home. Even a few days of noting how many minutes after a dose the benefit arrives, and how early it fades before the next one, makes for a far more concrete conversation at the appointment.
What you can do now
Both stories point the same way — the gut is bound up with Parkinson’s treatment more closely than it might seem. Neither one, though, is grounds for changing a medication or buying a new product today. What is worth doing is keeping track of two things — whether constipation is there, and how the timing of when the benefit arrives and when it fades is changing — and raising them at the next appointment.
This article is ParkinON’s plain-language summary of recently published research and news. It is not a substitute for medical diagnosis or treatment, and does not reflect approval or availability status in any specific country. Please talk to your care team about any questions regarding new treatments.