Irritable bowel syndrome (IBS) is one of the most common reasons people see their GP about their gut. It’s real, it can be miserable, and there’s a lot more that helps than most people are told. This guide explains how IBS is diagnosed in the UK, which treatments have good evidence behind them, and the order to try them in.
Key points
- IBS causes tummy pain or discomfort linked to bowel habits, often with bloating. It doesn’t damage the bowel or lead to cancer.
- It’s a problem with how the gut and brain communicate, which makes the gut more sensitive and changes how it moves. It isn’t “all in your head”.
- Simple blood tests are usually enough to rule out other conditions. Most people don’t need a camera test.
- Start with regular meals, adjusting fibre, and cutting back on caffeine, alcohol and fizzy drinks. If that isn’t enough, a low FODMAP diet can help, but it should be done with support from a dietitian, not on your own.
- Medicines and gut-focused talking therapies can help when diet alone isn’t enough.
What is IBS?
IBS is a long-term condition affecting the large bowel. It’s called a disorder of gut-brain interaction: the nerves in the gut become more sensitive, the muscles in the bowel wall may squeeze too fast or too slowly, and the communication between gut and brain is turned up. That’s why normal amounts of gas or stool can feel painful, and why stress can make symptoms flare.[2]
IBS is often grouped by the main bowel pattern: IBS with diarrhoea (IBS-D), IBS with constipation (IBS-C), or mixed (IBS-M), where it swings between the two. The type matters, because some treatments suit one type and not another.[2]
Symptoms
NICE suggests thinking about IBS if you’ve had any of these for at least 6 months:[1]
- tummy pain or discomfort
- bloating
- a change in your bowel habit
The diagnosis becomes more likely if the pain eases after opening your bowels, or comes with a change in how often you go or what your stools look like. Many people also notice:
- straining, urgency, or a feeling you haven’t fully emptied your bowels
- mucus in your poo
- symptoms that are worse after eating
- tiredness, backache, feeling sick, or bladder symptoms
See your GP promptly, rather than assuming it’s IBS, if you have:
- blood in your poo or bleeding from your bottom
- weight loss you can’t explain
- a change to looser or more frequent poo lasting more than 6 weeks, if you’re over 60
- a family history of bowel or ovarian cancer
- a lump in your tummy or back passage
- symptoms that wake you from sleep, or a fever
These don’t mean something serious is wrong, but they do need checking before IBS is diagnosed. If you have heavy bleeding or severe pain, call 999 or go to A&E.
How IBS is diagnosed
There’s no single test for IBS. Your GP makes the diagnosis from your symptoms, and uses a few simple tests to rule out other conditions. NICE recommends:[1]
- a full blood count, to check for anaemia
- inflammation markers (CRP, and ESR or plasma viscosity)
- a blood test for coeliac disease
If diarrhoea is a main symptom, your GP may also send a stool test called faecal calprotectin, which helps tell IBS apart from inflammatory bowel disease such as Crohn’s disease or ulcerative colitis.[3]
If these are normal and you don’t have warning signs, scans, colonoscopy and other tests aren’t usually needed. That can feel unsatisfying, but it’s a positive diagnosis, not a guess.[1,2]
Getting tested for coeliac disease? Keep eating gluten (for example bread or pasta at more than one meal a day) for at least 6 weeks before the blood test. Cutting it out first can make the test falsely normal. Our coeliac disease guide explains why.[4]
Step 1: everyday diet and lifestyle
These first-line changes come from NICE and BSG guidance, and help many people on their own:[1,2]
- Eat regular meals and take your time eating. Don’t skip meals or leave long gaps.
- Drink plenty, at least 8 cups of fluid a day, mostly water or other non-caffeinated drinks.
- Limit tea and coffee to 3 cups a day.
- Cut down on alcohol and fizzy drinks.
- Limit fresh fruit to 3 portions a day.
- If you have diarrhoea, avoid sorbitol, a sweetener found in sugar-free sweets, gum and some drinks.
- If you have wind and bloating, try adding oats or up to a tablespoon of linseeds a day.
- Be physically active. Regular exercise improves IBS symptoms for many people.
Fibre: the right kind matters
Insoluble fibre, such as bran, often makes IBS worse, especially bloating. Soluble fibre, such as ispaghula husk (Fybogel) or oats, is more likely to help, particularly with constipation. Increase it gradually over a few weeks.[1,2]
Probiotics
Some people find probiotics help, although it’s hard to predict which product will work. If you want to try one, take it daily for at least 4 weeks, and up to 12 weeks, at the dose on the pack. If nothing has changed by then, stop and save your money.[1]
Step 2: the low FODMAP diet
FODMAPs are types of carbohydrate that are poorly absorbed and ferment in the bowel, producing gas and drawing in water. They’re found in foods such as onion, garlic, wheat, beans, some fruits and milk.
The low FODMAP diet has good evidence for improving IBS symptoms, but it’s a second-line option, for when the first-line changes above haven’t been enough. It isn’t meant to be followed for ever. Guided by a dietitian, it usually has three stages:[2]
- Restriction: high-FODMAP foods are swapped for low-FODMAP alternatives, usually for about 4 to 6 weeks.
- Reintroduction: each FODMAP group is tested one at a time, to find out which ones affect you.
- Personalisation: you go back to eating as widely as you can, limiting only your own triggers.
Please don’t start low FODMAP on your own
NICE advises that dietary management beyond the first-line changes should only be given by a healthcare professional with expertise in diet, such as a registered dietitian, and BSG guidance recommends dietitian support for low FODMAP.[1,2] It’s restrictive, it’s easy to cut out more than you need to, and it can affect the healthy bacteria in your gut. It isn’t suitable if you’re underweight, have lost weight without trying, or have, or have had, an eating disorder.
Ask your GP to refer you to an NHS dietitian. If you go private, check the dietitian is registered with the Health and Care Professions Council (HCPC): “dietitian” is a protected title in the UK.
Fewer foods, not more
Before I worked in endoscopy, I was a clinical nurse specialist in nutrition support, caring for people who needed tube or intravenous feeding. That work showed me how much good nutrition matters, and it’s one reason I’m wary of anyone cutting out more foods than they need to.
A pattern I see often is someone who has cut out a long list of foods and still feels unwell, and is now worried about what’s left to eat. A short, structured low FODMAP trial with a dietitian, followed properly through the reintroduction stage, usually leaves people with a far more varied diet than they started with, and a clearer idea of what really affects them.
If you take one thing from this guide, let it be that IBS is real and treatable, and that there’s almost always another step to try.
Ben JohnsonAdvanced Clinical Practitioner, Gastroenterology
Step 3: medicines
Medicines are chosen according to your main symptom:[1,2]
| Main symptom | Medicines that may help |
|---|---|
| Pain or cramping | Antispasmodics such as mebeverine or hyoscine butylbromide, or peppermint oil capsules |
| Diarrhoea | Loperamide, taken as needed (for example before going out) or regularly at a low dose |
| Constipation | Soluble fibre, then laxatives such as macrogol. Lactulose is usually avoided because it can cause bloating. Prescription options such as linaclotide may be used if others haven’t worked |
| Ongoing pain despite the above | A low dose of a “gut-brain” medicine such as amitriptyline, usually taken at night |
Amitriptyline is an antidepressant, but in IBS it’s used at much lower doses to calm gut nerve signals and reduce pain. It is not being prescribed because anyone thinks you’re depressed. A large UK trial in 2023 (ATLANTIS) found it helped IBS symptoms when started at a low dose in primary care.[5]
Step 4: gut-focused talking therapies
Because IBS involves the gut-brain connection, therapies that work on that connection can help, even if you don’t feel stressed or anxious. Cognitive behavioural therapy (CBT) for IBS and gut-directed hypnotherapy both have good evidence. Some are available through the NHS, and there are evidence-based apps and online programmes. Ask your GP what’s available locally.[2]
Is it IBS, or something else?
Several conditions can look like IBS, which is why the first tests matter. Coeliac disease is the most important to rule out. Others include inflammatory bowel disease, bile acid diarrhoea, and microscopic colitis, which causes watery diarrhoea, mainly in older adults.[1,2] If your symptoms change, or new warning signs appear, ask your GP to think again rather than assuming it’s your IBS.
Living with IBS
IBS tends to come and go. Flares are often triggered by stress, illness, travel, poor sleep, periods, or changes in routine. Keeping a symptom diary for a couple of weeks can help you and your GP see patterns. You can download a free diary here.
Frequently asked questions
Can IBS turn into cancer?
No. IBS doesn’t damage the bowel and doesn’t increase your risk of bowel cancer. But IBS doesn’t protect you from other conditions either, so see your GP if your symptoms change or you notice any of the warning signs above. Take part in bowel cancer screening when you’re invited.
Is IBS caused by stress?
Stress doesn’t cause IBS on its own, but the gut-brain connection means stress can make symptoms worse, and IBS symptoms can be stressful. Treating both sides often works best.
Should I go gluten-free?
Not without being tested for coeliac disease first. Some people with IBS feel better cutting down on wheat, but that’s usually because of FODMAPs in wheat rather than gluten itself.
How long does it take for treatment to work?
Give each change a fair trial, usually 4 weeks for diet changes or probiotics, and several weeks for medicines such as amitriptyline, before deciding whether it’s helped.
References
- NICE. Irritable bowel syndrome in adults: diagnosis and management (CG61). 2008, updated 2017. https://www.nice.org.uk/guidance/cg61
- Vasant DH, Paine PA, Black CJ, et al. British Society of Gastroenterology guidelines on the management of irritable bowel syndrome. Gut 2021;70:1214–1240. https://pubmed.ncbi.nlm.nih.gov/33903147/
- NICE. Faecal calprotectin diagnostic tests for inflammatory diseases of the bowel (DG11). 2013. https://www.nice.org.uk/guidance/dg11
- NICE. Coeliac disease: recognition, assessment and management (NG20). 2015. https://www.nice.org.uk/guidance/ng20
- Ford AC, Wright-Hughes A, Alderson SL, et al. Amitriptyline at low-dose and titrated for irritable bowel syndrome as second-line treatment in primary care (ATLANTIS). The Lancet 2023;402:1773–1785.
