Study: Why L. acidophilus Alone Outperforms Multi-Strain Probiotics for IBS Pain

If you have IBS and have tried probiotics without success, you may have tried multi-strain products — supplements that combine several different bacterial strains, on the assumption that more diversity means more benefit. A double blind, clinical trial published in Alimentary Pharmacology & Therapeutics by Ringel-Kulka and colleagues found the opposite. When it comes to relieving abdominal pain and bloating in IBS patients, a single strain of L. acidophilus produced greater relief than the same strain combined with another probiotic — and the reason comes down to what the bacteria do to pain receptors in the gut lining.

What Did the Study Find?

The trial directly compared two formulations in IBS patients: L. acidophilus NCFM administered alone, and L. acidophilus NCFM combined with a second probiotic strain. Both groups included patients with IBS-C (constipation-predominant) and IBS-D (diarrhea-predominant). Researchers didn't just track symptom scores — they measured what was happening in the gut tissue itself, specifically the expression of two types of receptors in the colonic mucosa: mu-opioid receptors (MOR) and cannabinoid receptors (CB2).

The single-strain group showed greater increases in both receptor types — confirmed at both the gene expression and protein expression level — than the combination group. This translated directly into outcomes: L. acidophilus alone was more effective at alleviating acute abdominal pain and chronic bloating across both IBS subtypes.

What Are Mucosal Opioid and Cannabinoid Receptors?

MOR and CB2 receptors in the gut lining are part of the gut's own pain-dampening system. When these receptors are upregulated, pain signals from the gut are attenuated — the gut becomes less reactive to stimuli that would otherwise produce pain or discomfort. Unlike systemic pain medications that affect the whole body, L. acidophilus upregulates these receptors locally, in the tissue where IBS symptoms originate.

Why Did Single-Strain Outperform the Combination?

The study found that L. acidophilus alone drove greater MOR and CB2 receptor expression than L. acidophilus combined with the second strain. Adding a second probiotic didn't enhance the effect — it reduced it. The combination produced lower receptor expression than the single-strain formulation across both IBS subtypes. The study's conclusion was direct: L. acidophilus exhibited greater effectiveness when administered alone in alleviating acute abdominal pain and chronic bloating in patients with IBS-C and IBS-D.

Read the full study →