Irritable Bowel Syndrome (IBS)
IBS affects 1 in 5 UK adults. Low FODMAP diet, antispasmodics, Rome IV criteria and prescription treatment explained.
Irritable Bowel Syndrome (IBS)
Causes, subtypes, diagnosis, low FODMAP diet, and UK treatment options.
Key fact: IBS is the most common gastrointestinal condition diagnosed in UK primary care, affecting around 1 in 5 adults. It causes real, often debilitating symptoms — but crucially, it does not cause bowel damage and is not associated with an increased risk of bowel cancer. With the right combination of dietary changes, lifestyle modification and targeted medicines, most people achieve good symptom control.
What Is IBS?
Irritable bowel syndrome (IBS) is a chronic functional gastrointestinal disorder characterised by recurring abdominal pain associated with a change in bowel habit. “Functional” means the bowel looks structurally normal — there is no visible damage, inflammation or structural abnormality on investigation — but it does not function normally. IBS is a disorder of gut-brain interaction, not a disease of bowel tissue.
IBS significantly affects quality of life. People with IBS report higher rates of anxiety, depression, work absenteeism and reduced social participation than those without the condition. The psychological burden of IBS is as important to acknowledge and address as the physical symptoms.
IBS Subtypes
| Subtype | Abbreviation | Dominant bowel pattern | Key treatment focus |
|---|---|---|---|
| IBS with diarrhoea | IBS-D | Loose or watery stools; urgency; >3 bowel movements per day on symptomatic days | Loperamide; low FODMAP; antispasmodics; bile acid sequestrants if bile acid malabsorption suspected |
| IBS with constipation | IBS-C | Hard or lumpy stools; straining; <3 bowel movements per week on symptomatic days | Soluble fibre (ispaghula); osmotic laxatives (macrogol); low FODMAP; increased fluid intake |
| IBS with mixed bowel habits | IBS-M | Alternating between loose and hard stools; most common subtype in primary care | Symptom-directed treatment; low FODMAP; antispasmodics for pain |
| IBS unclassified | IBS-U | Meets IBS criteria but bowel habits do not consistently fit the other subtypes | As IBS-M; reassess subtype over time as patterns emerge |
Causes and Mechanisms
IBS does not have a single identifiable cause. Current understanding points to several overlapping mechanisms that vary between individuals:
Altered gut-brain axis
The gut and brain communicate bidirectionally via the enteric nervous system, vagus nerve and gut hormones. In IBS, this communication is dysregulated — the brain amplifies gut signals and the gut over-responds to normal stimuli. Stress and anxiety worsen symptoms through this pathway, explaining why IBS often flares during periods of psychological stress.
Visceral hypersensitivity
People with IBS have a lower pain threshold in the gut. Normal levels of gas or bowel distension that most people do not notice are perceived as painful by someone with IBS. This is not “imagined” pain — it represents a real difference in gut nerve sensitivity that can be measured objectively.
Abnormal gut motility
IBS-D is associated with accelerated gut transit; IBS-C with slowed transit. These motility abnormalities cause the characteristic stool changes and urgency. They are driven partly by altered gut serotonin signalling — over 90% of the body's serotonin is produced in the gut and plays a central role in regulating motility.
Post-infectious IBS
Around 10% of IBS cases begin after a documented episode of acute gastroenteritis (e.g. Campylobacter, Salmonella, norovirus). The infection triggers low-grade mucosal inflammation and changes in gut microbiome and nerve sensitivity that persist long after the acute infection resolves. Post-infectious IBS is most commonly IBS-D.
Gut microbiome dysbiosis
People with IBS show altered gut bacterial composition compared to healthy controls, though no single pattern is consistently found across studies. Small intestinal bacterial overgrowth (SIBO) may contribute in a subset of IBS patients, particularly those with bloating and IBS-D.
Psychological factors
Anxiety, depression and history of adverse life events are significantly more common in people with IBS than in controls. This does not mean IBS is “all in the mind” — rather, psychological factors alter gut-brain axis signalling in ways that can produce, amplify and perpetuate physical gut symptoms. Treating psychological comorbidity is often the most effective route to symptom control.
Symptoms
- Recurrent abdominal pain or cramping — often relieved partially by defecation
- Bloating and abdominal distension — often worse as the day progresses
- Change in stool frequency — more or fewer bowel movements than normal
- Change in stool consistency — harder (IBS-C), looser or watery (IBS-D), or alternating
- Urgency — sudden strong need to open the bowels, often distressing in IBS-D
- Feeling of incomplete emptying after defecation
- Mucus in the stool (without blood)
- Fatigue, nausea and back pain are common associated symptoms
Symptoms typically worsen with stress, certain foods, menstruation, and illness. They usually improve somewhat with defecation. The chronic, fluctuating nature of IBS — better periods followed by flares — is characteristic.
Diagnosis: Rome IV Criteria
IBS is diagnosed clinically. NICE recommends diagnosing on positive symptoms rather than extensive investigation, provided red flag features are absent. The current gold standard is the Rome IV criteria:
Rome IV: Recurrent abdominal pain, on average at least one day per week in the last three months, associated with two or more of the following: (1) related to defecation; (2) associated with a change in stool frequency; (3) associated with a change in stool form (appearance). Criteria fulfilled for the past three months with symptom onset at least six months ago.
NICE recommends the following investigations to exclude organic disease at diagnosis:
- Full blood count (FBC) — to exclude anaemia
- ESR or CRP — to exclude inflammation
- CA125 — in women, to exclude ovarian pathology if symptoms warrant
- Coeliac disease serology (tTG IgA + total IgA) — coeliac can mimic IBS exactly
- Stool calprotectin — if IBS-D or mixed, to help distinguish from inflammatory bowel disease
Colonoscopy and other investigations are not routinely required to diagnose IBS in people under 50 with no red flag features.
Red Flags Requiring Urgent Investigation
Do not attribute the following symptoms to IBS without investigation: rectal bleeding; unintentional weight loss; unexplained iron-deficiency anaemia; a palpable abdominal or rectal mass; new change in bowel habit in anyone aged 50 or over; a family history of bowel or ovarian cancer; symptoms that wake the patient from sleep; or onset of IBS-type symptoms after age 50 without a prior diagnosis. These require urgent clinical assessment and appropriate investigation.
Dietary Management
Dietary modification is the first-line treatment for IBS and should be offered to all patients before or alongside medication. NICE recommends the following first-line dietary advice:
- Eat regular meals — do not skip meals or leave long gaps between eating
- Drink adequate fluid (at least 8 cups/day), prioritising water and caffeine-free drinks
- Restrict caffeine to no more than 3 cups per day (coffee, tea, energy drinks)
- Reduce alcohol and fizzy drinks
- For IBS-D: limit fresh fruit to 3 portions per day; avoid sorbitol (artificial sweetener in sugar-free products)
- For IBS-C: consider increasing soluble fibre (oats, linseeds); avoid insoluble fibre (bran) which often worsens symptoms
- Keep a food and symptom diary to identify personal triggers
The Low FODMAP Diet
For patients who do not respond adequately to first-line dietary advice, NICE recommends the low FODMAP diet as a second-line dietary intervention. FODMAP stands for Fermentable Oligosaccharides, Disaccharides, Monosaccharides and Polyols — short-chain carbohydrates that are poorly absorbed in the small intestine and rapidly fermented by gut bacteria, producing gas and triggering IBS symptoms.
| FODMAP category | Examples of high-FODMAP foods | Low-FODMAP alternatives |
|---|---|---|
| Oligosaccharides (fructans, GOS) | Wheat, rye, onions, garlic, leeks, legumes | Oats, rice, potatoes, carrots, spring onion (green tops only) |
| Disaccharides (lactose) | Cow’s milk, yoghurt, soft cheese, ice cream | Lactose-free milk, hard cheese, lactose-free yoghurt |
| Monosaccharides (excess fructose) | Apples, pears, mangoes, honey, high-fructose corn syrup | Bananas, blueberries, oranges, strawberries, maple syrup |
| Polyols (sorbitol, mannitol) | Avocado, cauliflower, mushrooms, stone fruits, sugar-free products | Aubergine, courgette, tomatoes, grapes, table sugar |
The low FODMAP diet is conducted in three phases: (1) strict restriction for 4–8 weeks; (2) systematic reintroduction of FODMAP categories one at a time to identify personal triggers; (3) personalised long-term diet based on reintroduction findings. It should be undertaken with dietitian support — doing it alone without guidance risks nutritional inadequacy and unnecessary food restriction.
Evidence: Studies show 50–80% of people with IBS experience meaningful symptom improvement on low FODMAP. The reintroduction phase is essential — most people can tolerate some FODMAPs and the goal is a personalised, minimally restrictive diet rather than permanent total FODMAP exclusion.
Lifestyle and Psychological Approaches
- Regular exercise: Consistent evidence that aerobic exercise reduces IBS symptom severity; aim for 30 minutes at least 5 times per week
- Stress management: Mindfulness, relaxation techniques and stress reduction measurably reduce IBS symptom scores
- Cognitive behavioural therapy (CBT): NICE recommends CBT for IBS not responding to other treatments; strong evidence base for reducing symptom severity and improving quality of life
- Gut-directed hypnotherapy: NICE-recommended for IBS; comparable efficacy to CBT in clinical trials; most effective for generalised IBS symptoms
- Probiotics: Some evidence supports symptom benefit; Lactobacillus and Bifidobacterium strains most studied; patients should try a specific product for at least 4 weeks and discontinue if no benefit
Medicines for IBS
| Medicine | Type | Best for | Evidence and notes |
|---|---|---|---|
| Mebeverine | Antispasmodic | Abdominal cramping and pain (all subtypes) | Relaxes smooth muscle in the gut wall; taken 20 minutes before meals; well tolerated; first-line for pain per NICE |
| Hyoscine butylbromide (Buscopan) | Antispasmodic | Acute cramping and spasm | Available OTC; rapid onset; less evidence than mebeverine for chronic IBS but useful for acute episodes |
| Peppermint oil (Colpermin) | Antispasmodic (natural) | Bloating and abdominal pain | Enteric-coated capsules; comparable to mebeverine in some trials; good tolerability; first-line option per NICE |
| Loperamide | Antidiarrhoeal | IBS-D — loose stools and urgency | Reduces stool frequency and urgency; titrate to effect; does not treat abdominal pain |
| Ispaghula husk (Fybogel) | Soluble fibre supplement | IBS-C — constipation | Increases stool bulk and softness; must be taken with plenty of water; avoid insoluble bran |
| Macrogol (Laxido, Movicol) | Osmotic laxative | IBS-C — constipation | Draws water into the gut; softens stool; well tolerated; titrate dose to achieve comfortable stools |
| Low-dose amitriptyline | Tricyclic antidepressant (low dose) | IBS pain not responding to antispasmodics | 10–30mg at night; analgesic effect at doses below antidepressant range; slows gut transit (useful in IBS-D); second-line per NICE |
| SSRI (e.g. citalopram) | Antidepressant | IBS with predominant anxiety or depression; IBS-C (may speed transit) | Alternative if tricyclics not tolerated; less evidence than TCAs for IBS pain specifically; useful when psychological comorbidity prominent |
Get IBS Treatment Online
Access Doctor provides prescription IBS treatment — including antispasmodics, loperamide and low-dose amitriptyline — following a confidential online consultation with our GPhC-registered pharmacist independent prescribers. No GP appointment required.
View IBS Treatments →When to Seek Help
- Your bowel symptoms are significantly affecting your quality of life, work or sleep
- You have not been formally diagnosed with IBS — a clinical assessment is needed before self-treating
- Symptoms are not responding to dietary changes and first-line medicines
- You develop any red flag features (see above) at any time
- You have significant anxiety or depression alongside IBS — psychological treatment often produces better outcomes than medicines alone
Seek urgent medical assessment if you develop rectal bleeding, significant unintentional weight loss, a palpable abdominal mass, new bowel symptoms after age 50, or symptoms that wake you from sleep. These are not features of IBS and require investigation to exclude serious bowel pathology.
Frequently Asked Questions
What is IBS?
Irritable bowel syndrome is a chronic functional bowel disorder causing recurring abdominal pain associated with changes in bowel habit — diarrhoea, constipation or both. It affects around 1 in 5 UK adults. Crucially, it does not cause bowel damage and is not associated with an increased risk of bowel cancer.
What causes IBS?
IBS has no single cause. It involves altered gut-brain axis communication, visceral hypersensitivity, abnormal gut motility, changes in the gut microbiome, and psychological factors. Post-infectious IBS can develop after gastroenteritis. The relative contribution of each factor varies between individuals.
How is IBS diagnosed?
IBS is diagnosed clinically using the Rome IV criteria: recurrent abdominal pain at least one day per week, associated with changes in bowel frequency or form, for at least three months. NICE recommends diagnosing IBS on positive symptoms with a small number of blood tests to exclude organic disease, rather than extensive investigation.
What is the low FODMAP diet for IBS?
The low FODMAP diet restricts fermentable carbohydrates poorly absorbed in the small intestine. It involves a 4–8 week restriction phase, followed by systematic reintroduction to identify personal triggers, then a personalised long-term diet. Studies show 50–80% symptom response. Dietitian support is strongly recommended.
What medicines help IBS?
Antispasmodics (mebeverine, peppermint oil) are first-line for abdominal pain. Loperamide controls diarrhoea in IBS-D. Soluble fibre and osmotic laxatives help IBS-C. Low-dose amitriptyline (10–30mg nightly) is second-line for pain not responding to antispasmodics. SSRIs are an alternative when psychological comorbidity is prominent.
Can IBS be cured?
There is no cure, but IBS can be effectively managed. Most people achieve good symptom control through dietary changes, lifestyle modification, stress management and targeted medicines. Many find their IBS improves over time. Addressing psychological comorbidity — anxiety and depression — is often the most effective route to lasting improvement.
References
- National Institute for Health and Care Excellence (NICE). Irritable bowel syndrome in adults: diagnosis and management. NICE guideline NG61. Updated 2017. nice.org.uk/guidance/ng61
- NHS. Irritable bowel syndrome (IBS). NHS.uk, 2023. nhs.uk/conditions/irritable-bowel-syndrome-ibs
- Lacy BE et al. Bowel disorders. Gastroenterology. 2016;150(6):1393–1407. (Rome IV criteria)
- Staudacher HM, Whelan K. The low FODMAP diet: recent advances in understanding its mechanisms and efficacy in IBS. Gut. 2017;66(8):1517–1527.
Medical disclaimer: This article is for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional for diagnosis and treatment. In a medical emergency, call 999.
