In short: The gut and brain communicate constantly through nerves (including the vagus nerve), hormones, the immune system and gut bacteria. This "gut-brain axis" helps explain why stress and anxiety can upset digestion, and why ongoing gut symptoms can affect mood. Research on gut bacteria and mental health is promising but still early, so treatment focuses on proven steps: checking for medical causes, diet and lifestyle changes, and talking therapies where appropriate.

This guide, written by a Ready Health prescribing pharmacist, explains what the gut-brain link is, what the evidence does and does not show, and when to seek help in Wigan, Chorley, Bolton or Standish.

What is the gut-brain axis?

The gut-brain axis is the two-way communication system between your digestive system and your brain. It involves:

Nerves: the gut has its own extensive network of nerves, and the vagus nerve carries signals in both directions.
Stress hormones: stress can change how quickly food moves through the gut and how sensitive the gut feels.
The immune system: inflammation in the gut can send signals that affect the rest of the body.
The gut microbiome: the bacteria and other microbes living in the gut produce substances that may influence the body and brain.

Does the gut make serotonin?

Most of the body's serotonin is made in the gut, mainly by specialised cells in the gut lining, with gut bacteria influencing how much is produced. However, serotonin made in the gut does not cross into the brain directly. In the gut it mainly helps control bowel movement and sensation. So while the gut and mood are linked, it is an oversimplification to say your gut "makes your happy hormones".

How can stress and anxiety affect digestion?

Many people notice "butterflies", nausea, an urgent need for the toilet, or loss of appetite when anxious. Longer-term stress can make symptoms such as tummy pain, bloating, diarrhoea or constipation worse. This is especially common in irritable bowel syndrome (IBS), where the gut is thought to be more sensitive to normal signals.

Can gut problems affect mental health?

Living with ongoing gut symptoms can be stressful, disrupt sleep and affect work and social life, which can lead to low mood or anxiety. Studies also show differences in gut bacteria between people with and without some mental health conditions, but it is not yet clear whether these differences cause symptoms or result from them, and much of the evidence comes from animal studies.

Which conditions involve both gut and mind?

Irritable bowel syndrome (IBS)
Anxiety and depression, which often occur alongside gut symptoms
Functional dyspepsia (ongoing indigestion with no structural cause)
Inflammatory bowel disease (Crohn's disease and ulcerative colitis), where living with a long-term condition can affect wellbeing

What can help?

Approach	What the evidence suggests
Medical check	Rule out conditions such as coeliac disease, inflammation, infection or anaemia with appropriate blood or stool tests.
Regular meals and diet changes	NICE advises regular meals, enough fluids, and limiting caffeine, alcohol and fizzy drinks for IBS. Soluble fibre (such as oats) may help some people.
Low-FODMAP diet	Can help IBS, but should be supervised by a healthcare professional with dietary expertise, as it is restrictive.
Probiotics	If you want to try one, NICE suggests taking it for at least four weeks and stopping if there is no benefit.
Talking therapies	CBT and gut-directed hypnotherapy can help people with IBS whose symptoms continue despite other treatment, and CBT is effective for anxiety and depression.
Exercise, sleep and stress management	Physical activity and good sleep support both gut and mental health.

Be cautious about tests sold to "check your microbiome" or detect food intolerances through IgG antibodies. They are not recommended in UK guidance for diagnosing gut problems.

When should I see a doctor about gut symptoms?

Speak to a GP promptly if you have:

blood in your poo or black, tarry stools
unexplained weight loss
a change in your bowel habit that lasts several weeks, especially if you are over 50
a lump in your tummy, difficulty swallowing, or persistent vomiting
symptoms that wake you at night, or a family history of bowel or ovarian cancer, coeliac disease or inflammatory bowel disease

If you are struggling with your mental health and feel unsafe, call NHS 111 (select the mental health option), contact Samaritans on 116 123, or call 999 in an emergency.

Frequently asked questions

Can anxiety cause IBS?

Anxiety does not directly cause IBS, but stress and anxiety can trigger or worsen symptoms, and IBS can increase anxiety.

Should I take a probiotic for my mood?

There is not enough evidence to recommend probiotics for anxiety or depression. Speak to a healthcare professional about proven treatments.

Is hypnotherapy recommended for IBS?

NICE guidance supports considering psychological therapies, including hypnotherapy and CBT, for IBS that has not improved with other treatment.

Can a blood test show gut problems?

Blood tests can check for anaemia, inflammation and coeliac disease. Other tests, such as a stool test for inflammation, may also be needed.

Key takeaways

The gut and brain are closely connected in both directions.
Stress can worsen gut symptoms, and gut symptoms can affect mood.
Microbiome research is promising but not yet a basis for treatment.
Get red-flag symptoms checked and use evidence-based treatments.

Sources and further reading

Last reviewed: October 2026 by Shamir Patel, Independent Prescribing Pharmacist, Ready Health. This article is general information and does not replace advice from your own clinician.

If your gut and mood are affecting each other, Ready Health in Standish, serving Wigan, Chorley and Bolton, can help. Book a private GP appointment to discuss your symptoms and any blood tests, or ask about CBT and hypnotherapy.