IBS-C is constipation-predominant IBS. It might sound like a simple case of the bowel moving too slowly, but the reality is more complicated. IBS-C can involve several underlying mechanisms, including slower movement through the gut, heightened gut sensitivity, and altered gut-brain signalling.

These mechanisms can work alone or overlap. That’s why a treatment that works brilliantly for one person may do very little for another.

Understanding what is contributing to your IBS-C can help guide treatment. If you’re currently struggling to find something that works, you can also explore this ongoing clinical study for IBS with constipation.

Slow Transit Can Contribute to IBS-C

Normally, muscular contractions move waste progressively through the colon. During transit, water is gradually absorbed until the waste is firm enough to pass. However, if the transit slows further, more water is absorbed, making the stool harder and more difficult to pass.

This makes logical sense. But it’s not the case in all people with IBS-C.

Research has found delayed colonic transit in only a subset of patients, with one review estimating around 20%. This distinction is helpful, as it explains why simply speeding up the bowel will not resolve everyone’s symptoms.

Visceral Hypersensitivity Can Make Normal Gut Activity Painful

Slow transit only explains a subset of IBS-C cases. Another common factor is visceral hypersensitivity.

This means the nerves involved in detecting sensations from internal organs become unusually sensitive. Normal stretching of the bowel from stool or gas may therefore be experienced as disproportionate discomfort, bloating, or pain.

As with slow transit, not everyone experiences this. But it does explain why two different people with IBS-C can have radically different symptoms, and why treating constipation does not necessarily relieve abdominal pain.

The Gut-Brain Axis Can Affect Motility and Sensitivity

The gut has its own extensive network of nerves, sometimes called the “second brain.”

The gut and the brain constantly exchange information via these neural pathways as well as hormonal and immune signalling. These messages regulate intestinal movement, secretions, gut sensation, and response to stress.

When that communication changes, it can affect bowel function and sensitivity. This may help explain why symptoms sometimes change with stress or anxiety. It does not mean IBS is “all in your head.”

Gut Microbes and Methane May Slow Down the Bowel

Some people with IBS-C produce higher amounts of methane in the intestine. Strictly speaking, methane is produced primarily by methanogens, which are archaea rather than bacteria.

Higher methane levels detected via breath samples have been associated with slower intestinal transit and greater constipation severity. However, methane is not solely responsible for every case of IBS-C.

A methane breath test can be used in appropriate cases to measure methane production.

Pelvic Floor Dysfunction Can Make Stool Difficult to Pass

Going to the toilet is actually quite complicated. Your pelvic floor and anal muscles must relax and coordinate together to allow stool to pass.

With a defecatory disorder, sometimes called dyssynergic defecation, those muscles may struggle to relax or coordinate effectively, stopping stool from being able to pass.

Stool reaches the rectum, but difficulty coordinating those muscles can make it difficult to empty, leading to straining and incomplete emptying. Anorectal manometry testing measures pressure and muscle coordination which can help investigate the problem.

Why Is IBS-C So Difficult to Treat?

IBS-C does not have a single underlying mechanism. A treatment that helps one person may therefore do little for another.

Just making the stool softer with laxatives does not necessarily address visceral hypersensitivity, for example.

IBS-C is better understood as a syndrome that can emerge from different combinations of abnormalities rather than one disease.

How Can Specialists Investigate What Is Driving IBS-C?

Because IBS-C can have several underlying mechanisms, working out what is actually driving your symptoms can make a big difference. Specialists have a few tests that can look at different parts of bowel function:

You won’t necessarily need all these tests. It depends on your symptoms, what you’ve already tried, and what your doctor suspects is going on.

That’s also why research into IBS-C is still important. There isn’t one underlying cause or one treatment that works for everyone. If your current treatment has not provided enough relief, you can also learn more about this ongoing clinical study for IBS with constipation.

You might like to read the next article: IBS-C Treatment Not Working? What to Try Next in the UK