Mixed-Type Irritable Bowel Syndrome (IBS-M)

Irritable bowel syndrome mixed type (IBS-M) is a subtype of irritable bowel syndrome (IBS). When you have IBS-M, you experience all of the typical symptoms of IBS, but without a consistent bowel habit. You will find yourself dealing with episodes of both diarrhea and constipation. The changing nature of bowel symptoms can make it difficult to find strategies that bring about symptom relief.

A doctor talking with her patient
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Rome IV Criteria for IBS With Mixed Bowel Habits (IBS-M)

IBS is a functional gastrointestinal disorder diagnosed by applying standards known as the Rome criteria. The current version, Rome IV ("Rome 4") renames what was previously called "IBS with alternating bowel habits" (IBS-A) to "IBS with mixed bowel habits" (IBS-M). You are likely to continue to hear some people refer to it as IBS-A.

The other IBS subtypes are constipation-predominant IBS (IBS-C), diarrhea-predominant IBS (IBS-D), and IBS-unclassified (IBS-U).

The diagnostic criteria for IBS changed in Rome IV in four main ways::

  1. The defining symptom of IBS was changed from “abdominal discomfort or pain” to just “abdominal pain."
  2. The minimum abdominal pain frequency was increased from two or three days a month to once a week.
  3. Rome IV diagnosis only requires association of pain with defecation or changes in stools.
  4. The subtypes are based only on days in which abnormal stools occur.

This change allowed far more people who fell into the unclassified category (IBS-U) to have their disorder fall under one of the three classifications, but it also cut the rate of IBS diagnoses in half.

In addition to changes above, Rome IV requires that symptoms be present for at least the last three months, with the original onset at least six months before the diagnosis of IBS.

With the Rome IV criteria, many more people who used to be diagnosed with IBS are now diagnosed with functional diarrhea or functional constipation.

Symptoms of IBS-M

The Rome IV criteria define IBS-M as experiencing hard, lumpy stools (a Type 1 or Type 2 on the Bristol Stool Form Scale) during at least 25% of bowel movements on symptomatic days, and experiencing loose, mushy stools (a Type 6 or 7 on the Bristol Scale ) during at least another 25% of bowel movements on symptomatic days.

These stool changes can occur rapidly, over periods of hours or days. Or the predominant bowel problem may alternate between weeks or months of constipation and weeks or months of diarrhea.

People who have IBS-M can have all or some of the other symptoms associated with IBS:

  • Abdominal pain
  • A feeling of incomplete evacuation
  • Changes in bowel frequency
  • Changes in bowel movement texture
  • Gas and bloating
  • Mucus in the stool

If you are experiencing chronic episodes of constipation, diarrhea, or any of the other symptoms mentioned above, it is essential that you see your healthcare provider in order to obtain an accurate diagnosis. Some serious health problems share some of the same symptoms as IBS. Once you have the correct diagnosis, you can work with your healthcare provider on devising a treatment plan.

IBS Doctor Discussion Guide

Get our printable guide for your next healthcare provider's appointment to help you ask the right questions.

Doctor Discussion Guide Man

Prevalence of IBS-M

Not much data are available on how many people have IBS-M specifically. The American College of Gastroenterology (ACG) points out that about one half of people with IBS can change subtypes within the year, so regular reassessment of your IBS subtype is recommended.

One report found that a majority of IBS patients do experience an alternating pattern in terms of constipation and diarrhea, but do not necessarily describe themselves as having IBS-M.

Causes of IBS-M

With IBS-M, it can be difficult to understand how a person can have both constipation and diarrhea. The ACG acknowledges that more research is needed on IBS-M, and that it can be challenging to manage.

Researchers have been looking at the factors that might be behind IBS in general. These factors include:

A Word From Verywell

The challenge with the treatment of IBS is that you want to ensure that efforts to ease one bowel habit problem don't inadvertently result in the opposite problem. Working closely with your healthcare provider may help.

10 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  8. Moser G, Fournier C, Peter J. Intestinal microbiome-gut-brain axis and irritable bowel syndrome. Intestinale Mikrobiom-Darm-Hirn-Achse und ReizdarmsyndromWien Med Wochenschr. 2018;168(3-4):62–66. doi:10.1007/s10354-017-0592-0

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Additional Reading

By Barbara Bolen, PhD
Barbara Bolen, PhD, is a licensed clinical psychologist and health coach. She has written multiple books focused on living with irritable bowel syndrome.