Lactobacillus delbrueckii subsp. bulgaricus is a probiotic bacterium commonly used in the fermentation of yogurt. Its use for Irritable Bowel Syndrome (IBS) is supported by limited scientific evidence. Some studies have examined mixed probiotic formulations containing L. delbrueckii bulgaricus in addition to other strains such as Lactobacillus acidophilus and Bifidobacterium species. In these trials, modest improvements in IBS symptoms like bloating and abdominal pain have sometimes been reported. However, it is difficult to attribute these beneficial effects specifically to L. delbrueckii bulgaricus, as most studies do not use it as a single-strain intervention.

Systematic reviews and meta-analyses of probiotics for IBS generally find that certain probiotics may offer symptom relief, but the strength of evidence is moderate at best, and the efficacy appears to be strain-specific. L. delbrueckii bulgaricus has not been singled out as one of the most effective strains for IBS, and guidelines from gastroenterology associations suggest that while some probiotics may be tried, the evidence for specific strains—including L. delbrueckii bulgaricus—remains limited. Therefore, its use for IBS is justified by early scientific investigation, but the quality and quantity of evidence are relatively weak.