Probiotics: What Actually Works

What probiotics are

Probiotics are live microorganisms intended to confer a health benefit when consumed in adequate amounts. The two most studied categories are Lactobacillus species and Bifidobacterium species. A separate category, Saccharomyces boulardii, is a yeast with its own evidence profile.

Probiotic effects are strain specific. Lactobacillus rhamnosus GG is not interchangeable with Lactobacillus rhamnosus from a different source. The strain, the dose, and the formulation matter.

The situations with the most evidence

Antibiotic associated diarrhea

Several probiotic strains, particularly Saccharomyces boulardii and certain Lactobacillus rhamnosus strains, reduce the risk of antibiotic associated diarrhea. Start the probiotic when the antibiotic starts. Continue for 1 to 2 weeks after the antibiotic course. Take at least 2 hours apart from the antibiotic dose.

Acute infectious diarrhea

Some probiotic strains modestly shorten duration of viral diarrhea in children and adults. The effect is small but real.

Irritable bowel syndrome

Mixed evidence overall. Some strains improve symptoms in some patients. A trial of 4 to 8 weeks is reasonable. If no benefit by 8 weeks, the probiotic is likely not the answer.

Inflammatory bowel disease

VSL number 3 has evidence for pouchitis after surgery for ulcerative colitis. Evidence in active IBD is more limited.

Vaginal health

Specific Lactobacillus strains may help with recurrent bacterial vaginosis and yeast infections. Evidence is moderate.

Where evidence is weak or mixed

• General immune support claims. Limited evidence for healthy adults.
• Eczema and allergic conditions. Some pediatric evidence, limited adult evidence.
• Mental health and gut brain axis. Active research, currently weak evidence for clinical claims.
• Weight loss. Generally not supported.
• Most chronic disease prevention claims.

How to choose a product

• Look for specific strain identification including genus, species, and strain (e.g., Lactobacillus rhamnosus GG, not just Lactobacillus).
• Check that the CFU count (colony forming units) is at least 1 billion for general use, often 5 to 50 billion for specific indications.
• Verify the CFU count is guaranteed through the labeled expiration, not just at manufacture.
• Choose products from reputable manufacturers with quality certifications.
• Consider refrigerated products for some strains, shelf stable for others depending on the formulation.
• Match the strain to the indication based on published research.

Fermented foods as an alternative

Yogurt with live active cultures, kefir, sauerkraut, kimchi, and other fermented foods contain probiotic organisms. Less standardized than supplements but often a reasonable starting point for general digestive health. Choose products that say live and active cultures and avoid heat treated versions.

Safety and who should be careful

Probiotics are generally safe for healthy adults. Specific situations warrant caution.

• Immunocompromised patients, including those on chemotherapy or immunosuppressive medications.
• Patients with central venous catheters.
• Critically ill patients.
• Premature infants, in certain situations.

These situations call for clinical guidance rather than self treatment with probiotics.

When to talk to a pharmacist

• You are starting an antibiotic and want to know if a probiotic is appropriate.
• You have IBS and are considering a probiotic trial.
• You are immunocompromised.
• You are pregnant or breastfeeding.
• You take multiple medications.

This article is for general information only and is not a substitute for personalized medical advice. Before starting or changing any medication, including over the counter products and supplements, talk with your pharmacist or physician about your specific situation.