What is Irritable Bowel Syndrome (IBS)

Irritable bowel syndrome (IBS) is a common gastrointestinal disorder that causes abdominal pain and changes in bowel function. Bowel activity can fluctuate between overactive (diarrhea) and underactive (constipation).¹

IBS is one of the most common gastrointestinal disorders, affecting around 7-16% of the US population.² Symptoms have been linked to impaired gut-brain interaction and tend to overlap with other functional gastrointestinal conditions such as dyspepsia and gastroesophageal reflux disease (GERD).³ IBS can have a major impact on normal life, social activities, and work.

The exact causes of IBS are not certain, but it has several contributing factors that vary between individuals.

• Dysfunctional gut-brain interaction
  The gut-brain axis (GBA) is a complex line of communication between the central (CNS) and enteric nervous systems (ENS). This pathway can be influenced by genetics, hormones, diet, stress, the environment, neurotransmitter levels, and social input.
  Microbial imbalance in the gut can also affect brain-gut communication by altering chemicals, immune signals and pathways such as the HPA axis, which controls stress hormone levels in the blood.⁴
  
  
• Visceral hypersensitivity
  People with IBS tend to have higher visceral sensitivity, which means they have an exaggerated or abnormal sensitivity to otherwise non-painful stimuli in the gut and  internal organs, leading to sensations of pain or discomfort at lower thresholds than others. This sensitivity is believed to be due to increased signaling from intestinal receptors to the CNS in response to stimuli such as gas and bloating.⁵
  
  
• Poor gastrointestinal motility
  People with IBS may have slower gut motility or irregular contractions. Those with predominant constipation (IBS-C) often experience delayed transit, while those with predominant diarrhea (IBS-D) have faster motility.
  
  
• Dysbiosis
  Imbalances in gut bacteria are common in those with IBS-C and IBS-D. A 2025 review found consistent evidence of gut microbiota dysbiosis in people with IBS, including altered microbial diversity, composition, and metabolic function. Contributing factors included a reduced abundance of beneficial microbes, overgrowth of potentially harmful bacteria and disruptions between the gut-brain axis.⁶
  
  
• Genetics
  IBS is known to occur in families, which suggests a hereditary pattern. A large 2021 study confirmed six genes may be linked to IBS, including NCAM1, CADM2, PHF2/FAM120A, DOCK9, CKAP2/TPTE2P3 and BAG6. The first four are linked to mood and anxiety disorders and are active in the nervous system.⁷
  Mutations in the SCN5A gene, which affect sodium ion channels, have been linked to altered gut motility and abdominal pain in some people with IBS.⁸
  
  
• Food intolerances
  Food intolerances and sensitivities affect up to 65% of people with IBS.⁹ Common foods known to aggravate symptoms include dairy products, fruits and vegetables that contain fructooligosaccharides (such as onions, garlic, legumes, watermelon), wheat and gluten, caffeine, fried and fatty foods and carbonated beverages.
  
  
• Low-grade gut inflammation
  Inflammation due to gastrointestinal infection, diarrhea and/or allergic reactions can damage the gut lining, potentially leading to increased intestinal permeability and further inflammation.
  
  
• Psychosocial factors
  Up to one-third of people with IBS also experience anxiety or depression.¹⁰
  Stress, depression, anxiety and other psychological factors can impact intestinal sensitivity, motility and microbiota, potentially worsening IBS symptoms. 

IBS symptoms can change throughout life, but prevalence is higher in older people.

IBS symptoms may be accompanied by other functional digestive disorders and somatic pain conditions unrelated to the gastrointestinal tract.¹¹

IBS is currently categorized into four subtypes: IBS-C (constipation predominant), IBS-M (mixed bowel habits), IBS-D (diarrhea predominant) and unclassified IBS.

IBS symptoms according to subtypes: 

IBS with Constipation (IBS-C) 

• Frequent constipation
• Abdominal pain and constipation
• More than 25% of bowel movements are type 1 or 2 on the Bristol Stool Form Scale.

IBS-Mixed (IBS-M)

• Alternating between constipation and diarrhea
• More than 25% of bowel movements are type 1 or 2, and more than 25% are type 6 or 7 on the Bristol Stool Form Scale.

IBS with Diarrhea (IBS-D)

• Frequent loose or watery stools. 
• More than 25% of bowel movements are type 6 or 7 on the Bristol Stool Form Scale.

IBS-Unclassified (IBS-U)

• Symptoms meet the criteria for IBS, but bowel habits don’t fit other subtypes.

General IBS symptoms

• Abdominal pain or discomfort that is either relieved by defecation or associated with altered bowel frequency or stool form
• Bloating
• Flatulence
• Indigestions (dyspepsia, reflux)
• Changes in bowel habits
• Changes in the way stools are passed (straining, urgency, incomplete evacuation)
• Abdominal bloating, distension, tension, hardness
• Symptoms made worse by eating
• Mucus in the stools 
• Fatigue and lethargy
• Nausea
• Backache
• Bladder control problems 

Women are 1.5-3 times more susceptible to IBS than men, and report more intense abdominal pain, bloating and diarrhea. Women with IBS are also more likely to experience mood-related symptoms, including anxiety and depression. Researchers suggest that these differences may be due to hormonal fluctuations, particularly regarding estrogen and progesterone levels, which can affect gut motility, visceral sensitivity and immune responses in women. Women also tend to experience greater levels of stress. Gut microbiota also differs between men and women, which may play a role.¹²

Diagnosis of IBS is made by a general practitioner or other gastrointestinal specialist. This will typically involve a comprehensive casetake of health history and symptoms.

IBS Diagnostic Criteria, according to the Rome IV include:

• Recurrent abdominal pain on average at least one day of the week in the last three months, which changes according to bowel movements. This can mean:
• your symptoms improve or get worse after a bowel movement
• You have more or fewer bowel movements than before
• The appearance of your stools has changed

For example, a patient might have had pain in the lower abdomen with loose watery stools for the past five months, along with a persistent and often painful need to have a bowel movement, bloating and abdominal distention.

If you meet these criteria, your doctor may request blood tests to rule out other possible causes.

Laxatives and antidiarrheal medications are often used by IBS patients to treat symptoms, but these are not recommended as prolonged usage can have serious adverse effects.


Clinical treatment of IBS usually addresses the most severe symptoms, such as abdominal pain, diarrhea, constipation or bloating. 

Antispasmodics

Antispasmodic medications work by inhibiting smooth muscle contractions. They can help to regulate gastrointestinal motility, which can reduce pain and cramping in the gastrointestinal tract. However, evidence supporting the use of antispasmodics for the treatment of chronic abdominal pain in patients with IBS is limited, and some studies show they did not improve IBS symptoms compared with placebo.¹³

Antidepressants

Low-dose tricyclic antidepressants (TCAs) are preferred for gastrointestinal symptoms, particularly pain. However, studies suggest TCAs improve abdominal pain for only about 60% of patients (compared with about 30% on placebo) and also cause side effects such as drowsiness and dry mouth.¹⁴
Selective serotonin reuptake inhibitors (SSRIs) may be recommended if the patient also has a mood disorder, because low-dose TCAs are unlikely to address psychological symptoms.¹⁵
Unfortunately, the most common adverse effects of SSRIs are symptoms involving the digestive system, such as abdominal pain and nausea. Some clinicians recommend that neuromodulators should only be used as a second-line treatment.¹⁶
Methylfolate, on the other hand, has been shown to enhance the benefits of SSRIs and other antidepressants by facilitating the production of serotonin. Methylfolate does not cause gastrointestinal symptoms or any other adverse effects.¹⁷

A natural, holistic approach to managing IBS incorporates dietary modifications, supplements and lifestyle recommendations.

Diet

Patients with IBS often find that eating certain foods make their symptoms worse. Excluding these foods can be the best way to minimize symptoms.¹⁸

The low FODMAP diet is clinically shown to be a beneficial therapeutic approach for patients with IBS. FODMAPs are fermentable oligosaccharides, disaccharides, monosaccharides, and polyols: types of sugars present at different concentrations within specific fruits, vegetables, legumes, dairy products, artificial sweeteners and nuts. These sugars are found to be poorly absorbed in people with IBS, leading to symptoms.¹⁹

Recent trials have confirmed the effectiveness of the low FODMAP diet, particularly in relieving abdominal bloating and pain.²⁰

Soluble fibre

Psyllium husk (also known as ispaghula husk), is a form of soluble fibre that retains water in the colon, forming a gel in the colon.  For constipation, this gel helps to soften hard stools and encourage peristalsis. For diarrhea, the gel traps and absorbs excess water, slowing the movement of loose, watery stools. Psyllium is also fermented by bacterial enzymes, which supports the production of beneficial short-chain fatty acids along the whole colon.²¹

Peppermint oil

Peppermint oil is a naturally occurring carminative herb containing monoterpene compounds that target various symptoms of IBS. L-menthol blocks calcium channels in smooth muscle, producing antispasmodic effects on the gastrointestinal tract. Peppermint oil also harbours antimicrobial, anti-inflammatory and anesthetic properties. A 2019 meta-analysis found that enteric-coated peppermint oil is a safe and effective therapy for the relief of abdominal pain and overall symptoms in adults with IBS.²²

Ginger

Ginger is widely known for its gastrointestinal benefits, particularly in relieving nausea. It is one of the most commonly used natural remedies among IBS patients, and may support digestive function by stimulating digestive juices, promoting gastric motility, and relieving GIT discomfort.²³

Probiotics

People with IBS often have reduced microbial diversity and altered gut flora, including lower levels of beneficial bacteria (Lactobacilli and Bifidobacteria).²⁴ This is thought to contribute significantly to the development of IBS. 

Probiotics can help to restore healthy bacteria in the gut as well as help in producing essential nutrients, eliminating toxins, supporting immune cells, preventing harmful bacteria from spreading and strengthening the gut mucosal barrier.

A 2023 systematic review found that a combination of L. plantarum, L. casei, B. animalis, Streptococcus thermophilus and L. acidophilus were the most effective for improving overall quality of life in people with IBS, while B. longum was the most effective in improving anxiety and depression. Bacillus coagulans and Saccharomyces cerevisiae were also found to help with abdominal pain.²⁵

IBS is not usually associated with severe health issues. However, some people with chronic constipation may experience hemorrhoids or anal fissures due to slow bowel motility.
Restricting the diet can lead to nutritional deficiencies. For example, eliminating dairy may lead to lower calcium intake, unless calcium is replaced with other sources.

Stress and mood disorders can worsen IBS symptoms, reducing quality of life and interfering with work, relationships and social activities.

There is no ‘cure’ for IBS, but symptoms can be managed on a case-by-case basis, depending on what causes your flareups. This can involve changes to your diet, lifestyle and/or taking supplements. For example, some people may find that removing certain foods from their diet (such as high-FODMAP foods) and taking probiotics can help to relieve their symptoms.

Although IBS can cause pain and discomfort, IBD is associated with much more serious symptoms, including chronic diarrhea, abdominal pain, blood or mucus in the stool, unexplained weight loss and fatigue. People with IBDs such as ulcerative colitis and Crohn’s disease have an increased risk of developing colorectal cancer, especially if they are affected by long-term inflammation and scarring.²⁶

In addition, IBS does not cause structural damage to the gastrointestinal tract. IBD involves chronic inflammation that can injure the bowel lining. Crohn’s disease and ulcerative colitis are types of IBD, and may increase the risk of complications later in life, such as colorectal cancer.

Anxiety related to gastrointestinal symptoms can be a key driver of symptom severity and impaired quality of life in IBS. Up to one-third of people with IBS also experience anxiety or depression, primarily due to the gut-brain axis.²⁷

Longitudinal studies have shown that people who report symptoms of anxiety and/or depression tend to develop gastrointestinal symptoms over time, while many who do not have anxiety or depression at the time of diagnosis will develop these symptoms later on.²⁸

Delays in diagnosis and treatment can also worsen symptoms of anxiety and depression.

Methylfolate is often considered as part of a treatment plan for those with mood disorders (including anxiety and depression) as it enhances the production of serotonin, norepinephrine, and dopamine in the brain.²⁹