Diarrhoea

A different kind of diarrhoea, with more consistent evidence

Diarrhoea has many causes, and a stomach bug from a virus or bacteria is covered elsewhere on this site. One of the most common other causes is the antibiotics used to treat an unrelated infection, which disrupt the gut's own bacterial community as a side effect of killing the bacteria they're targeting. Antibiotic-associated diarrhoea affects up to 35% of people who take antibiotics. Unlike the probiotic evidence for ordinary stomach bugs, which has been mixed and partly reversed on closer inspection, the evidence for probiotics specifically preventing antibiotic-associated diarrhoea has held up consistently across many large, independent meta-analyses.

Consistent results across large meta-analyses

A 2021 meta-analysis of 36 trials, covering more than 9,300 people, found probiotics reduced the risk of antibiotic-associated diarrhoea by 38%. This built on an earlier, larger meta-analysis of 63 trials and nearly 11,800 people, which found a similar 42% reduction. A separate, more specific Cochrane review focused on Clostridioides difficile, a particularly serious cause of antibiotic-related diarrhoea, found probiotics roughly halved the risk, meaning for roughly every 65 people who took a probiotic alongside their antibiotics, one case was prevented.

Source: Probiotics for the Prevention of Antibiotic-associated Diarrhea in Adults

Source: Probiotics for the prevention of Clostridioides difficile-associated diarrhea in adults and children

Timing and strain both matter

Within these trials, starting the probiotic as early as possible during the antibiotic course, rather than after symptoms begin, was linked to a better protective effect. Certain strains showed a more consistent benefit than others, including specific Lactobacillus species and Saccharomyces boulardii, a beneficial yeast rather than a bacterium. As with any probiotic, taking a strain alongside antibiotics only helps if it's also given the fibre and plant compounds it needs to establish itself in a gut that's actively being disrupted by the antibiotic itself, rather than expecting the probiotic alone to hold the line.

What this means for you

Most antibiotic-associated diarrhoea is mild and resolves once the antibiotic course finishes, but watery diarrhoea that's severe, contains blood, or comes with fever needs medical attention, since it could signal a C. difficile infection that needs its own specific treatment. Given how consistent the evidence is here, asking a doctor or pharmacist about taking a specific probiotic strain alongside a prescribed antibiotic course is a reasonable, low-risk step, ideally started from the first dose rather than after symptoms appear. A varied, plant-rich diet supports the same gut bacteria this research is trying to protect during antibiotic treatment. That's the same idea behind GutLab, everyday gut health starts with regularly feeding the microbiome a broad range of plant-rich ingredients.