Supplement
Probiotics
Live microbes with strong strain-specific evidence and weak generic claims
Probiotics are live microorganisms sold as supplements or foods. We grade Probiotics C+ on evidence and C for worth-it at about $25-50 per month.
Evidence
Worth it
Typical cost: $25-50/month
What it does
Probiotics are live microorganisms sold as supplements or foods. Efficacy is strongly strain-specific and disease-specific: named strains have solid evidence for specific conditions, but generic multi-strain blends for general wellness have weak support.
What the research says
Specific strains reduce antibiotic-associated diarrhea and C. difficile risk
Evidence: strong. Strain-specificity meta-analysis: strong evidence for specific strains in AAD, CDI, IBS, acute pediatric diarrhea, and H. pylori support
Certain strains improve IBS symptoms
Evidence: moderate. Effects are strain-specific; genus-level pooling (all Lactobacilli, all Bifidobacteria) gives misleading results
Generic probiotics for general health in healthy adults lack consistent benefit
Evidence: weak. Healthy-adult trials are inconsistent; colonization is often transient and depends on the resident microbiome
Strong evidence exists only for specific strains and specific indications; as a generic category there is no single evidence grade, so generic products earn a conservative grade.
What the experts say
Every position links to its source. We include skeptics alongside supporters.
Tim Spector
“There's a lot of money in probiotics. They don't want to show that just having a cheaper food version is gonna do much better.”
Source, 2026-01-26 Skeptical of probiotic pills; argues a single-strain capsule may work for one person and not another, and that diverse fermented foods (kefir, kimchi) deliver far more microbial species than any capsule.
Michael Greger
“We just don't know enough about the microbiome to be able to use a few target species”
Source, 2025-03-20 Cautious: says we don't know enough about the microbiome to outsmart the body with a few target species, and flags that many fermented foods carry a sodium problem that offsets benefits.
Is it worth it?
Worth it only when a specific strain is matched to a specific indication; generic multi-strain blends for general wellness are a poor bet.
Typical cost
$25-50/month
Common form, not a brand recommendation
Dosage contextno established dose
Dose is strain- and indication-specific (typically 10^7 to 10^11 CFU); no generic dose exists for 'probiotics' as a category.
Safety notes
Generally safe in healthy adults. Immunocompromised, critically ill, or post-surgical patients should consult a clinician first. One reported study linked probiotic use to brain fog specifically in people with small intestinal bacterial overgrowth (SIBO); caution with SIBO.
Longevity Lab Report
Probiotics news, graded when it happens.
New studies, dose debates, and expert shifts on probiotics, in one email a week. Free.
Changelog
Last updated 2026-10-15
- 2026-10-15|Batch 2 DRAFT entry.