Condition

Irritable Bowel Syndrome (IBS)

Irritable bowel syndrome is a gut condition in which the brain-gut connection is disrupted, leaving the intestines oversensitive so normal signals bring pain, bloating, and changed bowel habits. Evidence is strongest for peppermint oil, where trials found symptoms improved, and probiotics, with moderate evidence, also eased abdominal pain. The peppermint effect was moderate in size across seven trials of 392 people, while prebiotics and synbiotics showed no clear difference in pain.

Sources: PMID 19507027; PMID 11148527

Supplements studied: 12
Graded outcomes: 13
Trials: 22
People studied: 733,259

Evidence by supplement

Strong
Moderate
Limited
Very limited

12 supplements

Peppermint

Peppermint: outcomes studied for Irritable Bowel Syndrome (IBS)
Grade	Outcome	Effect	Size	Studies	People
	Irritable Bowel Syndrome Symptoms Moderate Improvement	Improves (the measure goes down)	Moderate effect	7 studies	392 people
Studies that measured irritable bowel syndrome symptoms The effect of enteric-coated, delayed-release peppermint oil on irritable bowel syndromeDig Dis Sci · PMID 19507027 Enteric-coated, pH-dependent peppermint oil capsules for the treatment of irritable bowel syndrome in childrenJ Pediatr · PMID 11148527 Treating irritable bowel syndrome with peppermint oilBr Med J · PMID 389344 and 4 more on the Peppermint page
	Flatulence Small Improvement	Improves (the measure goes up)	Small effect		42 people
	Nausea Symptoms	Improves (the measure goes down)		4 studies	42 people
Studies that measured nausea symptoms Examination of the effectiveness of peppermint aromatherapy on nausea in women post C-sectionJ Holist Nurs · PMID 22034523 Peppermint oil: a treatment for postoperative nauseaJ Adv Nurs · PMID 9378876 An investigation into the use of aromatherapy in intrapartum midwifery practiceJ Altern Complement Med · PMID 10784271 and 1 more on the Peppermint page
	Subjective Well-Being	Improves (the measure goes up)			90 people

Melatonin

Melatonin: outcomes studied for Irritable Bowel Syndrome (IBS)
Grade	Outcome	Effect	Size	Studies	People
	Abdominal Pain Moderate Improvement	Improves (the measure goes down)	Moderate effect		115 people
	Irritable Bowel Syndrome Symptoms	Improves (the measure goes down)		1 study	115 people
Studies that measured irritable bowel syndrome symptoms The efficacy of exogenous melatonin supplement in ameliorating irritable bowel syndrome severity: A meta-analysis of randomized controlled trials.J Formos Med Assoc · PMID 36257872
	Quality of Life	Improves (the measure goes up)			115 people

Senna

Constipation Signs and Symptoms: improves
Intestinal Motility: improves

Senna: outcomes studied for Irritable Bowel Syndrome (IBS)
Grade	Outcome	Effect	Size	Studies	People
	Constipation Signs and Symptoms Large Improvement	Improves (the measure goes down)	Large effect	2 studies	519 people
Studies that measured constipation signs and symptoms Efficacy of senna versus lactulose in terminal cancer patients treated with opioidsJ Pain Symptom Manage · PMID 9436336 Safety and efficacy of a bulk laxative containing senna versus lactulose in the treatment of chronic constipation in geriatric patientsPharmacology · PMID 8234438
	Intestinal Motility	Improves (the measure goes up)		8 studies	519 people
Studies that measured intestinal motility Standardized senna in the management of constipation in the puerperium: A clinical trialS Afr Med J · PMID 6996138 The use of senna with docusate for postoperative constipation after pelvic reconstructive surgery: a randomized, double-blind, placebo-controlled trialAm J Obstet Gynecol · PMID 20207340 A volunteer model for the comparison of laxatives in opioid-related constipationJ Pain Symptom Manage · PMID 8935140 and 5 more on the Senna page

Probiotics

Abdominal Pain: improves
Bloating: improves
Irritable Bowel Syndrome Symptoms: improves

Probiotics: outcomes studied for Irritable Bowel Syndrome (IBS)
Outcome	Effect	Size	People
Abdominal Pain Moderate Improvement	Improves (the measure goes down)	Moderate effect	2,359 people
Bloating	Improves (the measure goes down)		702 people
Irritable Bowel Syndrome Symptoms	Improves (the measure goes down)		6,732 people
Quality of Life	Improves (the measure goes up)		732 people

Fecal Transplant

Bloating: improves
Abdominal Pain
Irritable Bowel Syndrome Symptoms: improves

Fecal Transplant: outcomes studied for Irritable Bowel Syndrome (IBS)
Grade	Outcome	Effect	Size	Studies	People
	Bloating Small Improvement	Improves (the measure goes down)	Small effect		164 people
	Abdominal Pain No effect		NoneNo effect		8,315 people
	Irritable Bowel Syndrome Symptoms	Improves (the measure goes down)		1 study	8,315 people
Studies that measured irritable bowel syndrome symptoms The Efficacy of Probiotics, Prebiotics, Synbiotics, and Fecal Microbiota Transplantation in Irritable Bowel Syndrome: A Systematic Review and Network Meta-Analysis.Nutrients · PMID 38999862

Vitamin D

Irritable Bowel Syndrome Symptoms
Plasma Vitamin D: improves
Quality of Life: improves

Vitamin D: outcomes studied for Irritable Bowel Syndrome (IBS)
Grade	Outcome	Effect	Size	Studies	People
	Irritable Bowel Syndrome Symptoms No effect		NoneNo effect	1 study	685,802 people
Studies that measured irritable bowel syndrome symptoms Impact of vitamin D supplementation on symptom severity and quality of life in patients with irritable bowel syndrome: A meta-analysis.Adv Clin Exp Med · PMID 39854263
	Plasma Vitamin D	Improves (the measure goes up)			780 people
	Quality of Life	Improves (the measure goes up)			685,802 people

Curcumin

Irritable Bowel Syndrome Symptoms
Pain: improves
Quality of Life: improves

Curcumin: outcomes studied for Irritable Bowel Syndrome (IBS)
Grade	Outcome	Effect	Size	Studies	People
	Irritable Bowel Syndrome Symptoms No effect		NoneNo effect	1 study	281 people
Studies that measured irritable bowel syndrome symptoms Nutritional Interventions in Adult Patients With Irritable Bowel Syndrome: An Umbrella Review of Systematic Reviews and Meta-analyses of Randomized Clinical Trials.Nutr Rev · PMID 39110917
	Pain	Improves (the measure goes down)		14 studies	281 people
Studies that measured pain Efficacy of Curcuma longa in relieving pain symptoms of knee osteoarthritis patients: a systematic review and meta-analysis of clinical trials.J Rheum Dis · PMID 39712249 Curcuma longa extract reduces inflammatory and oxidative stress biomarkers in osteoarthritis of knee: a four-month, double-blind, randomized, placebo-controlled trialInflammopharmacology · PMID 27761693 Efficacy and safety of curcumin and its combination with boswellic acid in osteoarthritis: a comparative, randomized, double-blind, placebo-controlled studyBMC Complement Altern Med · PMID 29316908 and 11 more on the Curcumin page
	Quality of Life	Improves (the measure goes up)			35,000 people

Asafoetida

Global Improvement: improves

Asafoetida: outcomes studied for Irritable Bowel Syndrome (IBS)
Grade	Outcome	Effect	Size	Studies	People	Studies list
	Global Improvement Cochrane review: very low quality evidence; one study showed improvement vs placebo, another showed no difference vs dicyclomine	Improves (the measure goes up)	Small effect		129 people

Prebiotics

Abdominal Pain
Bloating
Irritable Bowel Syndrome Symptoms: improves

Prebiotics: outcomes studied for Irritable Bowel Syndrome (IBS)
Outcome	Effect	Size	People
Abdominal Pain No effect		NoneNo effect	8,315 people
Bloating No effect		NoneNo effect	8,315 people
Irritable Bowel Syndrome Symptoms	Improves (the measure goes down)		8,315 people
Quality of Life	Improves (the measure goes up)		8,315 people

Synbiotics

Abdominal Pain
Bloating: improves
Irritable Bowel Syndrome Symptoms: improves

Synbiotics: outcomes studied for Irritable Bowel Syndrome (IBS)
Outcome	Effect	Size	People
Abdominal Pain No effect		NoneNo effect	8,315 people
Bloating	Improves (the measure goes down)		8,315 people
Irritable Bowel Syndrome Symptoms	Improves (the measure goes down)		8,315 people
Quality of Life	Improves (the measure goes up)		8,315 people

Aloe Vera

Irritable Bowel Syndrome Symptoms: changes; see studies

Aloe Vera: outcomes studied for Irritable Bowel Syndrome (IBS)
Grade	Outcome	Effect	Size	Studies	People	Studies list
	Irritable Bowel Syndrome Symptoms	Changes; see studies		1 study	151 people
Studies that measured irritable bowel syndrome symptoms Is Effective and Safe in Short-term Treatment of Irritable Bowel Syndrome: A Systematic Review and Meta-analysis.J Neurogastroenterol Motil · PMID 30153721

Pycnogenol

Irritable Bowel Syndrome Symptoms: changes; see studies

Pycnogenol: outcomes studied for Irritable Bowel Syndrome (IBS)
Grade	Outcome	Effect	Size	Studies	People	Studies list
	Irritable Bowel Syndrome Symptoms	Changes; see studies		1 study	77 people
Studies that measured irritable bowel syndrome symptoms Pycnogenol® supplementation improves the control of irritable bowel syndrome symptomsPanminerva Med · PMID 29737150

Key findings

Irritable Bowel Syndrome SymptomsPeppermintImproves (the measure goes down)
Abdominal PainMelatoninImproves (the measure goes down)
Constipation Signs and SymptomsSennaImproves (the measure goes down)

The Irritable Bowel Syndrome (IBS) protocol

2 primary supplements · 2 supporting supplements

Peppermint Oil200 mg enteric-coated capsules, 2–3× daily
Probiotics10–20 billion CFU daily (multi-strain)

See the full protocol

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Studies cited

13 studies from PubMed

Manipulation of dietary short chain carbohydrates alters the pattern of gas production and genesis of symptoms in irritable bowel syndromeJ Gastroenterol Hepatol · PMID 20659225
A Diet Low in FODMAPs Reduces Symptoms in Patients With Irritable Bowel Syndrome and A Probiotic Restores Bifidobacterium Species: A Randomized Controlled TrialGastroenterology · PMID 28625832
A Diet Low in Fermentable Oligo-, Di-, and Monosaccharides and Polyols Improves Quality of Life and Reduces Activity Impairment in Patients With Irritable Bowel Syndrome and DiarrheaClin Gastroenterol Hepatol · PMID 28668539
The Efficacy of the Low-FODMAP (Fermentable Oligosaccharides, Disaccharides, Monosaccharides, and Polyols) Diet in Irritable Bowel Syndrome: A Systematic Review and Meta-Analysis.Cureus · PMID 39917138
A Randomized Controlled Trial Comparing the Low FODMAP Diet vs. Modified NICE Guidelines in US Adults with IBS-DAm J Gastroenterol · PMID 27725652
Ehealth: low FODMAP diet vs Lactobacillus rhamnosus GG in irritable bowel syndromeWorld J Gastroenterol · PMID 25473176
A diet low in FODMAPs reduces symptoms of irritable bowel syndromeGastroenterology · PMID 24076059
Diet low in FODMAPs reduces symptoms of irritable bowel syndrome as well as traditional dietary advice: a randomized controlled trialGastroenterology · PMID 26255043
β-Galactooligosaccharide in Conjunction With Low FODMAP Diet Improves Irritable Bowel Syndrome Symptoms but Reduces Fecal BifidobacteriaAm J Gastroenterol · PMID 32433273
Long-term irritable bowel syndrome symptom control with reintroduction of selected FODMAPsWorld J Gastroenterol · PMID 28740352
Low FODMAP: A Preliminary Strategy to Reduce Gastrointestinal Distress in AthletesMed Sci Sports Exerc · PMID 28891824
The effects of low FODMAP diet on gut microbiota regulation: A systematic review and meta-analysis.J Food Sci · PMID 40035292
Effect of Pilates exercises on symptoms of irritable bowel syndrome in women: a randomized controlled trial.Arch Physiother · PMID 39822393

Evidence by supplement

Key findings

The Irritable Bowel Syndrome (IBS) protocol

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Studies cited

Related conditions

Supplement stack for Irritable Bowel Syndrome (IBS)