Treating Anxiety in Parkinson’s Disease with a Multi-Strain Probiotic: A Randomized, Controlled Trial
RESEARCHER: Dr. Joyce Lam
INSTITUTE: University of British Columbia
PROJECT GRANT: Graduate Student Award (2022 - 2024), $20,000 co-funded through a partnership between Parkinson Society British Columbia and the Parkinson Canada Research Program
Under the supervision of Dr. Silke Appel-Cresswell, Dr. Joyce Lam and colleagues at the University of British Columbia (UBC) sought to test whether a probiotic supplement could ease anxiety in people living with Parkinson’s disease (PD).
Anxiety is one of the most common, yet often overlooked, non-motor symptoms of PD. About 25–30% of people living with PD experience anxiety serious enough to interfere with daily life, and it can be just as disruptive to quality of life as tremor or stiffness. Current treatment options are rather limited: conventional medications used to treat anxiety don’t always work well for people with PD and can bring side effects such as drowsiness or an increased risk of falls.
In recent years, researchers have become increasingly interested in the “gut-brain axis” — the communication network linking the trillions of bacteria living in our gut (our “microbiome”) to the brain. Growing evidence suggests this connection may play a role in mood and anxiety, raising the possibility that probiotics, which are supplements containing live, beneficial bacteria, could offer a new way to ease anxiety symptoms.
To test this idea, Dr. Lam led the TAP trial (short name for Treating Anxiety in Parkinson’s Disease with a Multi-Strain Probiotic) as her PhD research project in Dr. Appel-Cresswell’s lab at UBC. This was the first randomized clinical trial specifically designed to evaluate whether probiotics can ease PD-related anxiety.
Sixty-one people with PD and clinically significant anxiety were randomly assigned to take either a nine-strain probiotic supplement or a placebo (an inactive product without bacteria, identical in appearance, taste, and smell) twice daily for 12 weeks. Neither participants nor the research team knew who was taking the probiotic until after the trial was fully complete. This “double-blind” design reduced bias, since participants knowing which treatment they received could affect how symptoms were reported, and researchers knowing could affect how data were collected. Anxiety in the trial was tracked using the Parkinson Anxiety Scale, a questionnaire designed specifically to capture the anxiety symptoms that people with PD experience.
By the end of the 12 weeks, anxiety scores had dropped substantially in both groups, with no meaningful difference between the probiotic and placebo groups. In other words, the probiotic did not outperform the placebo at easing anxiety. This finding, while not what the team had hoped for, likely reflects the fact that regular contact with a caring study team, increased awareness of one’s own symptoms, and the natural ebb and flow of anxiety over time can all drive meaningful improvement, regardless of whether someone received the probiotic or the placebo. Similar patterns have been observed in other PD anxiety trials testing cognitive behavioural therapy and acupuncture.
Interestingly, the team also uncovered an unexpected finding: participants taking the probiotic showed a small but statistically significant improvement on cognitive testing (memory, attention, and related thinking skills) compared with those on placebo. This finding should be interpreted cautiously, as the study was not designed to test cognition, and most participants started with relatively healthy cognitive scores, therefore leaving little room for a large change to be detected. Still, it echoes findings from other probiotic studies in aging and neurological populations, and points to a promising direction for future research. Importantly, the probiotic was very well tolerated, with high compliance and comparatively mild side effects. These side effects were mostly minor digestive symptoms in both groups.
While the results at this point do not support recommending probiotics as a treatment for anxiety in PD, they open the door to further investigation of their potential cognitive benefits. This study contributes to the growing effort to understand how gut health and brain health may be connected in PD, and points to areas worth exploring in future research on microbiome-targeted therapies. Building on this work, Dr. Appel-Cresswell’s team is now running a related trial testing a multi-strain probiotic for depressive symptoms in people with PD, and looks forward to sharing what they learn with the Parkinson’s community as the study progresses.
Dr. Joyce Lam completed her PhD in Neuroscience at the University of British Columbia in 2025 and is currently a Postdoctoral Research Fellow at UBC’s Pacific Parkinson’s Research Centre. Her research spans basic, translational, and clinical work on PD: during her master’s degree, she validated a rat model of PD using brain imaging techniques, and her doctoral work included leading the TAP trial. Looking ahead, she plans to continue researching PD, with a focus on its neuropsychiatric symptoms, working to bring more attention and better treatment to the non-motor side of the disease that so often goes unaddressed.
This content was published in the Fall 2026 edition of our quarterly magazine, Viewpoints. The content was accurate as of this publication date.