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Evidence-Based Supplement Research
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Lactobacillus plantarum 299v and Improved Irritable Bowel Syndrome Symptoms

Research synthesisModerate evidenceLarge effect4 studies · 3 beneficial · 1 neutral · 0 harmful

Across 4 studies, 3 reported beneficial effects of Lactobacillus plantarum 299v on irritable bowel syndrome symptoms, with effect sizes ranging from moderate to large. The predominant effect size is large, and one randomized controlled trial found 95% of patients improved vs 15% on placebo. The median study duration was 28 days, but effects have been reported with longer treatment (e.g., 12 weeks), and doses varied, with one study using 1×10^10 CFU/day.

  • Effective dose range: 1×10^10 CFU/day
  • Studied populations: patients with IBS

Caveats: Available evidence is overwhelmingly positive — clinical literature in this area is subject to publication bias (null-result studies are less likely to be published or indexed). Evidence base is small (only 4 studies) — conclusions should be considered preliminary. The largest study in the database (a meta-analysis, n=2643) did not find a significant effect for this specific strain, conflicting with smaller positive trials.

Generated Jul 17, 2026
Doses used in studies
  • CFU/day: 10 billion (median 10 billion, IQR 10 billion–10 billion) — 1 study
Time to effect
Median: 4 weeks · IQR 4 weeks–4 weeks · Range 4 weeks–4 weeks — Reported in 1 of 4 studies
Safety in these studies
4 of 4 papers
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