Irritable bowel syndrome (IBS-M)

What is IBS-M?

Irritable bowel syndrome with mixed bowel habit (IBS-M) is a subtype of IBS, not a separate disease and not a condition with its own licensed “IBS-M drug”. It sits beside IBS-C and IBS-D. People with IBS-M meet IBS criteria and have stools that alternate between constipation and diarrhoea patterns, rather than staying in one camp.

The NHS describes IBS as a common, long-term condition of the gut with pain or discomfort, bloating, and a change in bowel habit. Subtyping uses stool form (often the Bristol scale) on the days bowel habit is abnormal.

Rome IV (2016) and Rome V (2026)

Rome IV (2016) defined IBS by recurrent abdominal pain, on average at least one day per week, related to stool. People whose main sensation was discomfort rather than pain could fall outside that definition.

Rome V (2026) is the current Rome Foundation framework. For IBS it re-includes abdominal discomfort alongside pain, and uses a lower frequency threshold (recurrent pain or discomfort on average at least three days per month in the previous three months, with onset at least six months earlier for research criteria). Pain or discomfort should be recurrent, not continuous. Subtypes — IBS-C, IBS-D, IBS-M, and unclassified — remain the way clinicians group stool pattern.

NICE CG61 still uses the older clinical wording “abdominal pain or discomfort” associated with defecation or a change in bowel habit. That is closer to Rome V than to the stricter Rome IV pain-only rule.

NICE CG61: coeliac antibodies

When someone meets IBS criteria, NICE CG61 asks for blood tests that include antibody testing for coeliac disease (EMA or tTG), plus a full blood count and an inflammation marker (ESR, plasma viscosity, or CRP). That is why a gluten-free diet is not an IBS experiment to try instead of testing. If coeliac disease is present, the diagnosis and the diet are different. If it is not, gluten-free living is not an IBS treatment on its own. If your symptoms include diarrhoea days, the American College of Gastroenterology also suggests a blood test for coeliac disease before anyone treats this as IBS alone — the same safety step NICE CG61 already asks for. You can read that ACG 2021 suggestion (Lacy and colleagues) on PubMed.

CG61 also lists tests that are not required to confirm IBS when the criteria are met (including several scopes and breath tests). That does not stop a clinician investigating alarm features.

There is no IBS-M-specific medicine

There is no licensed medicine that exists only for mixed-bowel-habit IBS. Treatment follows the symptom in front of you, as NICE CG61 and the BSG 2021 guideline already describe.

Approaches people discuss

There is no medicine pathway only for IBS-M. Care follows the dominant stool pattern, reviewed with a clinician.

• Established NICE CG61 first-line diet and lifestyle advice, and medicines aimed at the dominant symptom, reviewed by a GP or gastroenterologist. NICE CG61 says to avoid lactulose. Prefer soluble fibre, not bran. ACG 2021 also suggests soluble fibre (for example ispaghula / psyllium), not insoluble bran, for global IBS symptoms. Titrate a laxative or loperamide toward Bristol stool type 4. Sources: NICE CG61; NHS IBS; BSG 2021; ACG 2021.
• Established Coeliac serology before any long-term gluten-free diet. Sources: NICE CG61.
• Emerging Dietitian-supervised low-FODMAP, then reintroduction — a time-limited assessment, not a forever restriction. Sources: NICE CG61; BSG 2021; Guts UK.
• Limited Gluten-free eating for IBS without coeliac testing, or supplements advertised as "for IBS-M".

Community insights

Anecdotal themes:

• People with IBS-M often feel they do not “fit” the constipation or diarrhoea leaflets — the sibling pages exist for that reason.
• Stool pattern can shift over months; subtype is a snapshot, not a personality type.
• Going gluten-free because a forum said “try it for IBS” is a recurring story. NICE still wants the antibody test first.
• Pain and discomfort both show up in how people describe their week. Rome V’s wording matches that better than Rome IV’s pain-only rule.