Supplement analysis backed by scientific evidence · PT

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Moderate evidenceGut health

Lactobacillus Acidophilus

The most famous probiotic species and the default filler in cheap multi-strain capsules, but almost all of its real evidence comes from a handful of specific strains (NCFM, CL1285, La-5) used in blends. Generic "acidophilus" on a label tells you nothing about whether it will work.

What the science says

  • Helps prevent antibiotic-associated diarrhea (specific strains) Moderate evidence

    In a dose-response RCT of 255 hospitalized adults on antibiotics, a formula of L. acidophilus CL1285 plus L. casei LBC80R at 100 billion CFU/day cut antibiotic-associated diarrhea to 15.5% vs 44.1% on placebo, and C. difficile-associated diarrhea to 1.2% vs 23.8%. The 50 billion CFU dose worked less well, and this benefit belongs to those two strains in combination, not to acidophilus generally.

  • Improves tolerance of lactose-containing dairy Moderate evidence

    L. acidophilus produces beta-galactosidase, and reviews of probiotic and prebiotic use in lactose maldigestion find that fermented or probiotic-supplemented dairy reduces breath hydrogen and symptoms in many lactose intolerant people. The effect is modest and largely explained by bacterial lactase delivered with the meal, so timing matters more than dose.

  • Reduces IBS symptoms Limited evidence

    The 2023 Gastroenterology systematic review of 82 probiotic RCTs in IBS found the category as a whole beats placebo for global symptoms, but rated most individual strains as low-certainty and could not identify acidophilus specifically as an effective single strain. Combination products containing it are more often positive than acidophilus alone.

  • Colonizes the gut long term Limited evidence

    It does not. Stool studies consistently show L. acidophilus disappears within roughly 1-2 weeks of stopping supplementation. Any benefit requires continuous daily intake, which is the main reason "reseed your gut once" marketing is wrong.

Dosage & safety

Studied doseStudied doses run 1-100 billion CFU/day, most commonly 1-10 billion CFU/day for digestive endpoints and 100 billion CFU/day for antibiotic-associated diarrhea prophylaxis. Take alongside or shortly after antibiotics rather than skipping them, separated by about 2 hours. Choose a product that names the strain designation (e.g. NCFM, La-5, CL1285), not just the species.
SafetyVery safe in healthy people; the usual complaints are transient gas and bloating in the first week. Rare bacteremia and endocarditis cases have been reported in the severely immunocompromised, patients with central venous catheters, short bowel syndrome, or critical illness — probiotics should not be given routinely in the ICU or to patients with acute pancreatitis. Products are regulated as foods or supplements, so CFU counts at expiry are frequently lower than the label claims.

Scientific references

Where to buy

21st Century, Acidophilus Probiotic Blend, 150 Capsules

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