Probiotics vs Microbiota-Based Medicines

Definitions

• Probiotics are live microorganisms intended to have health benefits when consumed or applied to the body. They are found in yogurt and other fermented foods, supplements and beauty products. [1]
• Live biotherapeutic products (LBPs) is a regulatory term. FDA guidance on early trials covers LBPs, including some that are lawfully marketed as foods or dietary supplements and are proposed for clinical uses regulated as drugs. [2] See Live Biotherapeutic Products.
• Fecal microbiota products are made from donated human stool. For example, Vowst contains live bacteria and is manufactured from human fecal matter donated by qualified individuals. [3] See Fecal Microbiota-Based Therapies.

The difference at a glance

What the research shows

Probiotics. NCCIH says probiotics have shown promise for several purposes and that much remains to be learned about whether they help or are safe for various conditions. [1] Effects depend on the strain: if one kind of Lactobacillus helps prevent an illness, that does not mean another kind would. [1] For C. difficile diarrhea during antibiotic treatment, a 2017 analysis of 31 studies concluded it is moderately certain that probiotics can reduce the risk, mostly in hospital patients. [1] Evidence label: promising but limited. Strain details are in Probiotic Strains and Labels.

Fecal microbiota medicines. SER-109, an oral microbiome therapy, was tested in a randomized, double-blind, placebo-controlled phase 3 trial of 182 enrolled adults with repeated C. difficile infection. Recurrence within 8 weeks was 12% with the product and 40% with placebo, and the trial was funded by the manufacturer. [5] In the FDA's description of the trial behind Vowst's approval, recurrence through 8 weeks was 12.4% with Vowst versus 39.8% with placebo. [3] The most common side effects reported more often than with placebo were abdominal bloating, fatigue, constipation, chills and diarrhea. [3] Evidence label: approved medicine (FDA, for the indication above, read 2026-10-22).

Keep these apart

• A probiotic study does not show a fecal microbiota medicine works, and the reverse is also true.
• Approval of Vowst or Rebyota covers preventing recurrent C. difficile infection after antibiotics, not general gut health, and not other conditions. [3][4]
• A "microbiome" sold as a supplement is not the same as a licensed medicine. Do-it-yourself stool transfers are outside the scope of this page, and even a donor-screened product may carry a risk of transmitting infectious agents. [3]