• Most people with fibromyalgia also have irritable bowel syndrome, far more than chance alone would predict.
• Both conditions involve an oversensitive nervous system that reads normal signals as pain.
• Your gut and brain talk constantly through the vagus nerve, which helps to explain why the two flare together.
• Around 90% of your serotonin is made in your gut, linking digestion with mood, sleep and pain.
• Support works best when it’s joined up, looking after your gut, sleep, stress and nervous system together.

If you live with fibromyalgia, there’s a good chance your gut gives you trouble too. Most people with fibromyalgia also have irritable bowel syndrome. In clinic, the two so often turn up together that I’ve come to expect it. Researchers increasingly think it’s more than a coincidence.

On the surface, these look like two separate problems in two separate parts of the body. Irritable bowel syndrome brings tummy pain and changes in your bowel habits. Fibromyalgia brings widespread muscle pain and tenderness. The evidence, though, tells a more connected story.

A large 2024 study looked at more than 1.2 million hospital admissions, all for irritable bowel syndrome. The researchers found fibromyalgia in around one in ten of these people. That’s roughly five times the rate in the general population. There is other research that puts the overlap higher still, with some studies finding irritable bowel syndrome in up to seven in ten people with fibromyalgia.

Fibromyalgia brings pain and stiffness to your neck, shoulders, elbows, knees, lower back and hips. The pain is often severe. Stress and physical effort tend to make it worse.

Alongside the pain, most people notice fatigue and headaches, often of the migraine type. Poor sleep, memory trouble and difficulty concentrating are common too.

Our understanding of fibromyalgia has moved on a great deal. It’s now described as a form of central sensitisation. In plain terms, that means your nervous system turns up the volume on pain. Normal signals from your muscles and joints get read as pain, even when there’s no damage or inflammation to explain it. The rheumatologist Daniel Clauw, who has studied this for years, calls fibromyalgia the clearest example of this kind of pain.

Fibromyalgia muscle also looks different under the microscope. Those differences reduce energy production and blood flow in the muscle. That can make both the pain and the fatigue feel worse, which fits what many women describe to me.

Something similar happens in irritable bowel syndrome. Researchers call it visceral hypersensitivity, which is really the gut’s version of the same turned up volume. The nerves in your gut wall become oversensitive. Normal digestion, and gas that most people wouldn’t notice, gets read as real pain.

Several studies have looked at gut bacteria in people with fibromyalgia. One found small intestinal bacterial overgrowth in every fibromyalgia patient tested. The worse the overgrowth, the worse their fibromyalgia tended to be.

Small intestinal bacterial overgrowth is also a major driver of irritable bowel syndrome. Where methane producing microbes are involved, researchers now prefer the term intestinal methanogen overgrowth. These microbes can grow beyond the small intestine, so the older name no longer quite fits.

Bacterial overgrowth changes how your bowel works. It can also change how sensitive the nerves in your gut wall become. That fits the visceral hypersensitivity seen in irritable bowel syndrome. One idea is that in fibromyalgia, this same gut driven oversensitivity reaches further, and adds to the widespread tenderness felt in the muscles.

So why would a gut problem and a muscle problem be linked at all? The answer is in the constant conversation between your gut and your brain. Researchers call this the gut-brain axis. It’s a two way line, carrying messages in both directions all day long.

The main connection in this line is the vagus nerve. It runs from your brainstem down to your gut, and it reports back on everything happening in your digestion. When this system becomes oversensitive, ordinary signals get amplified on the way up. That’s the same turned up volume we see in both conditions. It appears in the muscles on one hand, and the gut on the other.

A 2025 review looking at the two conditions together found that they share several of these routes. Immune activity, gut bacteria, nerve signalling and the gut-brain axis all came up as common ground. That doesn’t mean one causes the other. It means they share underlying mechanisms, so treating them as two unrelated problems often misses what is driving them both.

Most people are surprised to learn that around 90% of your body’s serotonin is made in your gut, not your brain. It’s produced by special cells in the gut lining that respond to your food and your gut bacteria.

Serotonin does a lot of work down there. It helps to drive the muscle contractions that move food along, and it shapes how sensitive your gut feels. When serotonin signalling is disturbed, digestion and gut pain can both be affected. That’s one reason it’s so often involved in irritable bowel syndrome.

Serotonin matters for mood and sleep too, though the gut supply and the brain supply are kept separate. Still, the overlap is telling. Low mood, poor sleep and a sensitive gut often cluster together in fibromyalgia. Serotonin helps to regulate each one, which is why it keeps coming up. It’s one of those threads I find really useful when I’m making sense of the whole picture.

Stress is the thread that ties much of this together. When you’re under sustained pressure, your body raises cortisol through a system called the HPA axis. In short bursts that’s healthy. Kept switched on, it starts to cause problems.

One of those problems is a more permeable gut lining, sometimes called a leaky gut. This lets bacterial products cross into the bloodstream, where they can stir up low grade inflammation. That inflammation reaches the nervous system and can turn up pain signalling further. Researchers have linked this stress driven pattern to both fibromyalgia and irritable bowel syndrome.

This doesn’t make the pain any less real. Stress acts as an amplifier on an already sensitive system, rather than inventing the problem. That’s why calming the nervous system tends to help both the gut and the muscles. I never treat stress as a side issue.

A few nutrient patterns come up again and again in fibromyalgia. Vitamin D is often low, and several studies link low levels with more severe pain. Trials on topping it up have had mixed results, though a recent review found it reduced pain scores overall. It’s worth having your level checked, especially through the darker months here in the UK.

Magnesium has been studied too, alongside tryptophan. Your body needs tryptophan to make serotonin and melatonin. Low serotonin is linked with low mood and anxiety. Low melatonin can disturb your sleep. None of these explains fibromyalgia on its own. They’re part of a wider picture worth understanding, alongside other factors such as your coenzyme Q10 status.

So, fibromyalgia and irritable bowel syndrome may not always occur together, but there is real overlap, and this can point to where support is worth starting.

Begin with the foundations. I have found that looking after the gut often calms the wider pattern, since so much of this runs through your digestion. Dietary approaches such as low FODMAP have good evidence for irritable bowel syndrome, including for people who also have fibromyalgia. It works best done properly, as a short structured trial rather than a permanent restriction, ideally with guidance.

Sleep and stress belong here too. Good sleep gives your nervous system time to settle, and a calmer stress load takes some of the amplification out of the pain. Gentle, graded movement helps more than rest over time, even when that feels counterintuitive. And where nutrient levels are low, correcting them can ease the load, including vitamin D and coenzyme Q10.

Set on these foundations, everything else has a better chance of working.

Because the gut and the nervous system are so tangled together here, I rarely work on one alone. Herbs are chosen to fit the person, and a few groups come up often.

Carminative herbs, such as peppermint, fennel and chamomile, are traditionally used to ease bloating, cramping and trapped wind. Peppermint in particular has been studied for irritable bowel syndrome, and it has a calming effect on the gut wall. Bitter herbs, and herbs that soothe the gut lining, can support digestion where it feels sluggish or reactive.

Alongside these, I often look at nervine herbs, such as skullcap and lemon balm, which are traditionally used to calm an overstretched nervous system. Since stress amplifies both the gut and the pain, settling the nervous system is often where real change begins.

Traditional use of herbs provides a lot of guidance for herbalists, and the research on herbs for these conditions is still growing. That’s exactly why they benefit from individual prescribing by a medical herbalist. She can match the right herb, form and dose to you, and check it fits safely with any medicines you take.

A few gentle habits are worth a try. Eat regularly and slowly, and notice which foods settle you and which stir things up. Protect your sleep as far as you can, since it helps both your gut and pain. Build in some small ways to calm your nervous system. That might be slow breathing, a warm bath, time outdoors, or some gentle movement you enjoy. Not dramatic on their own, but together, and repeated, they can add up.

It also helps to track how you feel across a few weeks. Note your energy, sleep, pain and digestion side by side. Patterns often appear that a single bad day would hide, and they give you something useful to work from.

Fibromyalgia and irritable bowel syndrome are not two separate problems that happen to appear together. They grow from an oversensitive nervous system, a busy gut-brain conversation, and the effects of stress over time. Seen that way, the fact they occur together makes sense.

When your gut and your pain flare together, that isn’t a coincidence. It reflects how closely they are connected, and supporting one often helps the other.

A note on care. If you take prescribed medicines, check with a herbalist who knows your case before starting herbs. And it’s always sensible to see your GP about new or persistent changes to your digestion, so anything that needs their input isn’t missed. This is educational information, not personal medical advice.