Prebiotics and probiotics have been incorporated into clinical practice with a degree of ease that contrasts with the complexity of the evidence supporting their use. Part of this acceptance may be explained by their perception as “natural” and, therefore, harmless interventions.

However, one of the most common errors is treating probiotics as a therapeutic category. The available evidence requires a far more precise approach, moving away from generic and abstract concepts toward the clinical use of specific strains and defined doses for clearly established indications.

Indications With Evidence

Probiotics are live microorganisms that confer health benefits to the host when administered in adequate amounts.

The strongest evidence supports their use in antibiotic-associated diarrhea and, to a lesser extent, in acute infectious diarrhea. Multiple systematic reviews and clinical guidelines have concluded that certain strains reduce symptom duration and the risk for diarrhea, although effect sizes are modest and vary by product. Efficacy cannot be extrapolated across commercial formulations, even when they share the same bacterial genus.

Some guidelines suggest probiotics in carefully selected individuals for the prevention of Clostridioides difficile infection. Recommendations remain weak and emphasize the need to assess individual risk profiles. A similar scenario applies to pouchitis, defined as inflammation of the ileoanal pouch in individuals with inflammatory bowel disease who have undergone total colectomy. In this setting, specific multistrain combinations provide compelling evidence. These findings should not be generalized to other manifestations of inflammatory bowel disease.

In highly prevalent outpatient conditions such as irritable bowel syndrome, the evidence is heterogeneous. Some studies have reported modest benefits for symptoms such as abdominal bloating, but the results are inconsistent and depend on both the strain used and patient subgroups. Probiotics may benefit certain individuals; however, they do not represent a universally applicable recommendation with predictable outcomes.

Prebiotics, which are nondigestible substances that selectively stimulate the growth or activity of potentially beneficial bacteria, can modulate the gut microbial ecosystem and improve functional symptoms. Their effects are frequently dose-dependent. Higher doses may exacerbate gastrointestinal symptoms, limiting their clinical applicability.

In the general population, probiotics and prebiotics are usually associated with mild, transient gastrointestinal adverse effects. However, this safety profile should not be assumed to be universally applicable.

In immunocompromised or critically ill individuals, in those with severe disruption of the intestinal barrier, and in those with central venous catheters, cases of bacteremia and fungemia attributed to probiotic microorganisms have been reported. Although rare, this complication is clinically significant. In such contexts, caution should take precedence over potential benefits, given the limited evidence supporting its use.

Concerns have also been raised regarding the potential transfer of antimicrobial resistance genes from probiotic strains to the intestinal microbiota. This possibility underscores the need for well-characterized products that undergo rigorous safety evaluations.

Clinicians should select specific microorganisms for defined indications when recommending probiotics. Strains such as Lactobacillus rhamnosus and Saccharomyces boulardii have been evaluated in antibiotic-associated diarrhea, whereas Bifidobacterium longum BB536 has some evidence in chronic constipation.

Even in these scenarios, clinicians should clearly communicate the expected benefits and limitations, particularly because the formulations are not always commercially available.

Available evidence indicates that prebiotics and probiotics may be beneficial for specific clinical indications. However, they are not broadly generalizable interventions and do not consistently produce clinically meaningful effect sizes. Although it can be difficult to look at past commercial messaging and social trends, clinicians have a responsibility to critically evaluate the available data, including its nuances and limitations, and translate them into individualized clinical decisions.

Further research focused on specific strains, their risk for adverse effects, and outcomes with clear clinical relevance is essential to clarify a field in which uncertainty outweighs established evidence.

The authors’ conflicts of interest are available in the original article.

This story was translated from Univadis Spain, part of the Medscape Professional Network.