Probiotic supplements
Also called: probiotics, live bacterial supplements.
Last reviewed 2026-09-16. How this works.
When to call your team
If your immune system is suppressed by treatment, contact your care team the same day if you notice:
- a fever, or feeling hot and shivery
- feeling suddenly very unwell or faint
- redness, pain or swelling around a drip line
Bacteria from probiotic capsules have been traced into the bloodstream of critically ill patients by genetic sequencing. The event is rare and none of those patients died of it. These are reasons to make a phone call. They are not a diagnosis, and this page cannot tell you what is causing them.4
These are reasons to make contact, not a diagnosis. Whatever you are taking or thinking of taking, the people treating you can only weigh it if they know about it.
This block is about what to watch for, and it is not all this page holds: an interaction recorded against a treatment class and what has been recorded about harm are below. Nothing in this block is an all-clear for a question it does not mention.
Improving immunotherapy response Grade D
No human evidence of benefit, or none that survived testing.
Harm has been recorded in people for this claim. The grade measures how strong the evidence for benefit is; it says nothing about the harm, and the two are read from different parts of this page.
In the melanoma studies, people taking probiotics did worse, not better, than those who did not.
The signals point the wrong way in the setting studied most.
The harm
Six critically ill children grew the same Lactobacillus strain in their blood that they were being given as a probiotic. The investigators sequenced the isolates and traced the organism from capsule to blood rather than inferring it from timing, which is proof rather than coincidence.4
Some of the probiotic bacteria, once established in the gut, had acquired a mutation conferring antibiotic resistance.4
The scale matters and the book corrects itself here. The event is rare, none of those patients died of it, and in the companion case-control work most cases were mild or judged to be contamination. It belongs on this page anyway, because the mechanism is proven rather than suspected, and because the people it happened to were immunocompromised.4
The claim
The claim is that a probiotic supplement improves the gut microbiome and therefore improves how well immunotherapy works. It follows naturally from the fibre entry and it is where the microbiome story stops being simple.
What it does
A supermarket probiotic contains a few strains chosen largely because they survive manufacturing. Whether they establish themselves in a gut already full of organisms, and whether they are the right ones, are separate questions and neither is answered.
The evidence
In the melanoma study that supports the fibre entry, roughly a third of those surveyed were taking a probiotic, and the signal for probiotic use ran in the opposite direction to the fibre signal.1
A small study of antibiotic preconditioning before a probiotic in melanoma reported worse survival. The chapter note records that this was reached through a review rather than the primary study.3
One defined preparation is genuinely different and the book says so. Two randomised trials in metastatic kidney cancer of a single named strain alongside immunotherapy, pooled, reported substantially longer progression-free survival. Four things separate that from a supermarket probiotic: one defined strain, a registered trial, random assignment, and a published result anyone can check.2
Two cautions belong with it. Both trials are phase 1 and open-label, so promising rather than established. And the pooled abstract was published with an error and formally corrected, the corrected figures differing substantially, so which set is definitive must be established from the corrected record.2
The studies this rests on
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Pooled randomised phase 1 trials of a defined live bacterial supplement in metastatic renal cell carcinoma (NCT03829111)2
A meta-analysis, summarising randomised trials, phase 1, measured a clinical outcome.
longer progression-free survival with the defined strain; the pooled abstract was published with an error and formally corrected.
about hazard ratio 0.44, interval 0.22 to 0.88. as first published, P=0.02; the correction reports substantially different figures and the corrected record governs
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Probiotic use among melanoma patients receiving immunotherapy1
An observational study, measured a clinical outcome, 158 participants.
probiotic use associated with a signal running opposite to the fibre signal.
What is absent
No randomised trial has tested an over-the-counter probiotic alongside immunotherapy. The randomised evidence in this record is for one defined strain in one cancer, and it does not transfer to a product bought off a shelf.
Scope: over-the-counter probiotics and immunotherapy response.
Established by trial scope, checked 2026-09-16. Result: the randomised trials in this record tested a single named strain in metastatic renal cell carcinoma.21
What to ask
The register records an observational signal that probiotics may run against immunotherapy, so does that change anything for me?
The dish-to-person gap
These are live organisms rather than a compound, so no pharmacokinetic profile applies.
Interactions
The signal recorded here runs against checkpoint immunotherapy, which is a treatment class. It is observational and it points the opposite way to what most people expect from a probiotic.1
Probiotic supplements alongside checkpoint immunotherapy
Recorded as documented, against Checkpoint immunotherapy.
Does taking a probiotic supplement matter while I am on immunotherapy?
The whole interaction list, and how to turn it into a pharmacy review request.
Find a trial instead
One defined strain is in registered randomised trials, which is a different thing from a supermarket probiotic.
Search ClinicalTrials.gov for recruiting studies of probiotic OR Clostridium butyricum
A trial is the same decision with monitoring, a known preparation and a doctor who knows what else you are taking.
References
Spencer CN, McQuade JL, Gopalakrishnan V, et al, and 86 further authors. Dietary fiber and probiotics influence the gut microbiome and melanoma immunotherapy response. Science 2021;374(6575):1632-1640.
doi:10.1126/science.aaz7015 · NCT04645680
How this was reached: transcribed from chapter note, via docs/CHAPTER-NOTES.json, chapter 23 note 7. The author string is abbreviated in the source that was read and has not been expanded.
Dizman N, Meza L, Bergerot P, et al. Nivolumab plus ipilimumab with or without live bacterial supplementation in metastatic renal cell carcinoma: a randomized phase 1 trial. Nature Medicine 2022;28(4):704-712. Pooled analysis: Moradi A, et al, Journal of Clinical Oncology 2026;44(7 suppl):507.
doi:10.1200/JCO.2026.44.7_suppl.507 · NCT03829111
How this was reached: transcribed from chapter note, via docs/CHAPTER-NOTES.json, chapter 23 note 8. The author string is abbreviated in the source that was read and has not been expanded.
The Journal of Clinical Investigation review of the gut microbiome and cancer response to immune checkpoint inhibitors.
No persistent identifier recorded.
How this was reached: transcribed from chapter note, via docs/CHAPTER-NOTES.json, chapter 23 note 9.
Yelin I, and colleagues. Genomic and epidemiological evidence of bacterial transmission from probiotic capsule to blood in ICU patients. Nature Medicine 2019.
How this was reached: transcribed from chapter note, via docs/CHAPTER-NOTES.json, chapter 23 note 10. The author string is abbreviated in the source that was read and has not been expanded.