Probiotics, defined as live microorganisms that confer a health benefit when consumed in adequate amounts, have become increasingly popular in holistic health fields in recent years . Probiotics can help restore the balance of the gut microbiota, which plays many important roles in human health. Emerging research has explored the potential benefits of probiotics for a range of health conditions. This article provides an evidence-based overview of the role of probiotics for specific gut health conditions, based on findings from randomized controlled trials.
Probiotics for Irritable Bowel Syndrome (IBS)
Multiple randomized controlled trials show that certain probiotics help reduce symptoms of irritable bowel syndrome (IBS) . IBS is a common disorder characterized by recurrent abdominal pain and altered bowel habits. In a systematic review of 37 randomized trials, consensus statements with a high level of evidence indicated that specific probiotics help alleviate IBS symptoms and abdominal pain in some patients . The strain with the strongest evidence was Bifidobacterium, as it was the most commonly used strain in many of the studies .
Looking at specific IBS subtypes, there is moderate evidence that certain probiotics improve overall symptoms in diarrhea-predominant IBS (IBS-D). For constipation predominant IBS (IBS-C), the level of evidence is weaker, with 80% consensus agreement among experts . More research is needed to clarify effects on IBS subtypes. Probiotics may benefit bloating, bowel function and quality of life in some IBS patients. However, no single probiotic alleviates all IBS symptoms . This highlights the need to select specific strains based on the clinical context and patient symptoms.
Continued high-quality research is warranted, especially on multi-strain formulations, optimal dosing, duration of treatment, head-to-head comparisons of different probiotics, and longer-term follow-up. However, the current evidence supports a therapeutic trial of specific probiotics as a supplement to standard IBS care.
Probiotic Treatment of Antibiotic-Associated Diarrhea (AAD)
Multiple systematic reviews and meta-analyses provide a high level of evidence that certain probiotics help prevent antibiotic-associated diarrhea (AAD) [1,3]. AAD is a common side effect of antibiotic therapy that occurs due to disruption of the gut microbiota. In a meta-analysis of 63 randomized controlled trials, probiotic use significantly reduced the risk of developing AAD compared to control groups not receiving probiotics .
The most beneficial strains for AAD include Lactobacillus GG, Saccharomyces boulardii and multi-strain formulations. Probiotics are thought to help restore the gut microbiota altered by antibiotic treatment. Experts recommend specific probiotics as adjuvant therapy to help prevent or reduce AAD in patients receiving antibiotics .
Very few studies have evaluated probiotics for treating AAD once it develops, so additional studies are warranted in this setting as well. Overall, probiotics show clear promise for prevention of AAD, but further research could help refine optimal strains, dosing and duration of treatment after onset. For more information on how antibiotics can affect your gut health, check out our Blog Post: Antibiotics and the Microbiome.
Coupling Helicobacter Pylori Therapy with Probiotics
Similar to antibiotics, Helicobacter pylori eradication therapy often causes diarrhea as an adverse effect. Multiple randomized trials provide promising evidence that certain probiotics (Lactobacillus GG, Saccharomyces boulardii, and other multi-strain formulations) are helpful as adjuvant therapy to prevent or reduce the associated diarrhea [1,3]. The beneficial effects may relate to stabilization of the gut microbiota disrupted by the antibiotic component of H. pylori eradication therapy.
However, some uncertainty remains about optimal probiotic regimens. Additional larger trials focused on pinpointing the ideal strains, doses and treatment durations could help solidify consensus recommendations for probiotics as adjuvant therapy in H. pylori eradication protocols. Current evidence supports their use to help mitigate the risk of antibiotic-associated diarrhea from amoxicillin, azithromycin, and clarithromycin .
Probiotics and Inflammatory Bowel Disease (IBD)
The evidence showing that probiotics helps inflammatory bowel disease (IBD) is more limited compared to other conditions. Some randomized trials suggest certain probiotics may help induce remission or prolong remission periods in ulcerative colitis, but more research is needed before specific recommendations can be made . For Crohn's disease, probiotics have generally not shown benefit in clinical trials . Experts conclude there is currently insufficient evidence to recommend probiotics for routine use in IBD, though further research should be pursued given the promising signals in some studies .
It has been hypothesized that dysbiosis and reduced microbial diversity may contribute to IBD, providing a rationale for probiotic intervention . It remains unclear whether microbiota changes are the cause or result of intestinal inflammation in IBD. Some studies have found promising effects of certain probiotics on remission in ulcerative colitis. Multi-strain formulations may hold the most potential. Additional randomized placebo-controlled trials are required to substantiate the benefit of probiotics as adjunctive therapy for IBD. Identifying optimal strains, dosing, duration of treatment and patient subpopulations most likely to respond, will help refine therapeutic applications of probiotics for IBD.
Probiotics Effect on Gastrointestinal Conditions
There is significant effort and attention placed on identifying specific benefits of probiotics for other gastrointestinal conditions like diarrhea, constipation, lactose intolerance, gas, bloating and functional GI disorders. However, research in many of these areas is limited or findings are mixed. Some studies suggest benefits of certain probiotics (e.g. Lactobacillus GG, S. boulardii) for infectious diarrhea, especially in children, though effects are variable across different probiotic strains, doses and clinical contexts . More research is needed to provide specific, evidence-based recommendations for most functional and motility-related GI conditions.
For instance, a few small studies reported improvements in constipation with certain multi-strain probiotics, but consensus guidelines do not currently recommend probiotics for treatment of chronic constipation . Probiotics may help relieve symptoms like bloating, distension and flatulence in some patients with functional GI disorders based on limited evidence. Larger rigorous trials are needed examining multi-strain probiotics on the full range of GI symptoms. Probiotics also show promise for reducing symptoms of lactose intolerance, but strain-specific recommendations cannot yet be made. More research could help refine the role of targeted probiotic therapies for these common GI complaints.
How Probiotics Can Help Immune Function and Allergies
Probiotics have been extensively studied for their immunomodulatory properties. Certain strains may help regulate inflammatory pathways and enhance gut barrier function . Some randomized trials show beneficial effects of specific probiotics for reducing risk of certain allergies . However, the heterogeneity across studies makes consensus recommendations challenging at this stage.
An additional finding is that probiotics may help counteract dysbiosis implicated in the “hygiene hypothesis” of increasing allergy prevalence . Clinical studies are examining whether early probiotic supplementation reduces incidence of allergies later in childhood.
Results have been mixed depending on the probiotic strains and dosing used. Additional randomized controlled trials are needed to clarify the efficacy of perinatal probiotic interventions for allergy prevention. Identifying optimal strains, timing and duration of administration will help translate the promising basic immunomodulatory effects of probiotics into clinically meaningful allergy outcomes.
How Probiotics Benefit Mental Health
An emerging area of research is examining psychobiotic effects of certain probiotics strains on mental health conditions like depression and anxiety. While findings are preliminary, some randomized controlled trials suggest specific probiotic formulations may improve depressive symptoms and reduce risk of depression in non-depressed individuals . However, many questions remain about the optimal strains, dosing and mechanisms.
The intestinal microbiota interact bidirectionally with the brain via the “gut-brain axis.” Animal studies have shown behavioral and cognitive effects of certain probiotics. Early clinical research provides proof-of-concept that probiotics targeting the gut microbiota could impact mood and cognition in humans as well.
For example, one randomized trial found that volunteers who took Lactobacillus helveticus R0052 and Bifidobacterium longum saw improved symptoms in patients with major depressive disorders . Much more interdisciplinary research is needed to substantiate psychobiotic effects in humans and provide implications for preventing and treating psychiatric conditions with probiotic therapies. Regardless, this information represents a promising new frontier in microbiome-brain research.
Safety of Probiotics
An advantage of probiotics is their favorable safety profile, especially compared to many other gut-health focused medications. Most randomized controlled trials report no difference in adverse events between probiotic and placebo groups 1-4. However, a majority of these studies were short-term. Caution is advised in treating immunocompromised patients, where isolated cases of infection have been linked to certain probiotics. Overall, probiotics meeting quality manufacturing standards are generally regarded as safe, but their long-term safety requires further study.
In general, probiotics should be avoided in seriously ill, hospitalized patients. Rare cases of bacteremia and fungemia have occurred, primarily in critically ill people with risk factors like immune deficiency. Otherwise, probiotics are well tolerated in most healthy individuals and patient populations. Safety monitoring is still warranted, especially with increasing popularity of probiotic supplements for long-term use. Further pharmacovigilance research can clarify the safety profile of chronic probiotic ingestion.
In summary, the strongest evidence supports targeted use of specific probiotic strains for conditions like IBS, antibiotic-associated diarrhea and Helicobacter pylori therapy. For other conditions, more research is needed to provide evidence-based recommendations, given the heterogeneity of probiotic strains and clinical contexts. When selecting a probiotic supplement, it is essential to choose an appropriate strain supported by randomized controlled trials for the intended use. Probiotics show promise as a supplement to conventional treatment methods for certain gastrointestinal, infectious, mental health and immune conditions, but should not replace standard medical care.
Continued advances in microbiome research may allow more personalized selection of probiotics based on individual gut microbial profiles. But currently, probiotics should be empirically chosen based on the underlying condition rather than microbiota testing. Further high-quality randomized controlled trials are critical to establish the efficacy and safety of probiotics for more clinical indications. If you are interested in learning more about how probiotics may help improve the symptoms of a health condition, try out GutChat, our gut-health specialized AI ChatBot, visit our Frequently Asked Questions, or reach out to an Injoy team member at email@example.com so we can get you started on your journey to a balanced gut.
 Hungin, A. P., et al. “Systematic Review: Probiotics in the Management of Lower Gastrointestinal Symptoms in Clinical Practice - an Evidence-Based International Guide.” Alimentary Pharmacology & Therapeutics, vol. 38, no. 8, 2013, pp. 864–886, https://doi.org/10.1111/apt.12460.
 M.-J. Butel, et al. “Probiotics, Gut Microbiota and Health.” Médecine et Maladies Infectieuses, 28 Nov. 2013, www.sciencedirect.com/science/article/pii/S0399077X13003077.
 Susanne Hempel, PhD. “Probiotics for the Prevention and Treatment of Antibiotic-Associated Diarrhea: A Systematic Review and Meta-Analysis.” JAMA, 9 May 2012, jamanetwork.com/journals/jama/article-abstract/1151505.
 Huang, Ruixue, et al. “Effect of Probiotics on Depression: A Systematic Review and Meta-Analysis of Randomized Controlled Trials.” MDPI, 6 Aug. 2016, www.mdpi.com/2072-6643/8/8/483/htm?utm_source=deleted&utm_medium=deleted&utm_term=deleted&utm_content=deleted&utm_campaign=deleted&gclid=deleted.