Irritable bowel syndrome

Irritable Bowel Syndrome (IBS) is a chronic gut disorder that affects bowel movements, digestion, and gut sensitivity. Serotonin (5-HT) plays a major role in IBS because it regulates:

• Intestinal motility (speed of digestion)

• Bowel movements (diarrhea or constipation)

• Gut sensitivity (pain, bloating, cramping)

• Brain-gut communication (mood, anxiety, stress response)

Since you have IBS-D (diarrhea-predominant IBS), food intolerances, and gut issues, it’s important to understand how serotonin affects IBS and how to balance it naturally.

How does Serotonin Affect IBS Symptoms?

• About 95% of serotonin is produced in the gut, where it controls digestion. Too much or too little serotonin leads to different types of IBS:

Serotonin Level	IBS Type	Symptoms
High Serotonin	IBS-D (Diarrhea-predominant IBS)	Frequent diarrhea, urgency, cramping
Low Serotonin	IBS-C (Constipation-predominant IBS)	Hard stools, bloating, slow digestion
Fluctuating Serotonin	IBS-M (Mixed IBS - Alternating D & C)	Alternating diarrhea & constipation

People with IBS often have serotonin imbalances, which cause unpredictable gut symptoms.

High Serotonin and IBS-D (Diarrhea)

• Frequent, urgent diarrhea

• Loose, watery stools

• Post-meal diarrhea (Dumping Syndrome)

• Abdominal pain and bloating

Causes of High Serotonin in IBS-D

• Gut Inflammation: Triggers excessive serotonin release.

• Stress & Anxiety: Increase gut serotonin, leading to diarrhea.

• Certain Foods (high-FODMAP, spicy foods): Trigger serotonin spikes.

• SSRI Medications: Some antidepressants increase serotonin, worsening IBS-D.

• Serotonin-Secreting Tumors (Rare): Carcinoid tumors cause chronic diarrhea.

Low Serotonin and IBS-C (Constipation)

• Hard, dry stools

• Infrequent bowel movements

• Bloating and gas

• Straining during bowel movements

Causes of Low Serotonin in IBS-C

• Poor gut microbiome: Reduces serotonin production.

• Low fiber diet: Leads to sluggish digestion.

• Chronic stress depletes serotonin over time.

• Vitamin deficiencies (B6, D, Magnesium): Affect serotonin synthesis.

Fluctuating Serotonin and IBS-M (Mixed IBS)

• Some people with IBS experience alternating diarrhea and constipation because serotonin levels rise and fall unpredictably.

Serotonin Cycle in IBS-M:

• High serotonin → Fast digestion → Diarrhea

• The body compensates by lowering serotonin → Slow digestion → Constipation

• Serotonin rises again. → Diarrhea returns

Irritable bowel syndrome

Irritable Bowel Syndrome (IBS) and noradrenaline dysregulation, especially through the gut-brain axis. Noradrenaline, also known as norepinephrine, is a stress-related neurotransmitter that plays a major role in regulating gut function, particularly in IBS patients.

How Noradrenaline Affects IBS:

Stress and Sympathetic Activation

Noradrenaline is released during stress via activation of the sympathetic nervous system ("fight or flight" mode). Chronic stress leads to persistently high levels of noradrenaline, which disrupts normal gastrointestinal function.

Altered Gut Motility

Noradrenaline can either increase or dysregulate gut motility, depending on receptor sensitivity. In IBS-D (diarrhoea-dominant), it tends to speed up intestinal contractions, while in IBS-C (constipation-dominant), it may slow down peristalsis, creating discomfort and bloating.

Visceral Hypersensitivity

Noradrenaline sensitizes gut nerve endings, making IBS patients more sensitive to normal gut movements—leading to pain, cramping, and urgency even without clear physical causes.

Microbiome Disruption

Chronic stress and noradrenaline influence the gut microbiome, reducing beneficial bacteria and promoting dysbiosis, which is strongly associated with IBS flare-ups.

Inflammation & Gut Barrier Integrity

Noradrenaline may increase intestinal permeability ("leaky gut") and low-grade inflammation, both of which are seen in many IBS cases.

IBS is not just a digestive disorder—it’s a gut-brain communication breakdown, often driven by hormonal imbalances.

Adrenaline

Adrenaline is your immediate stress responder. During moments of high stress or anxiety, adrenaline stimulates the gut, leading to cramping, urgency, or diarrhea. Over time, chronic adrenaline surges contribute to gut hypersensitivity, making your digestive system overreact to even mild triggers.

GABA (Gamma-aminobutyric acid)

GABA is the body's natural calming neurotransmitter. It helps regulate nerve signals in the brain and the gut. Low GABA levels reduce this calming effect, causing gut overstimulation, spasms, and worsening IBS symptoms like bloating and urgency—especially when you're feeling emotionally overwhelmed.

DHEA (Dehydroepiandrosterone)

DHEA supports stress resilience and gut barrier protection. When DHEA is low, the body becomes more vulnerable to gut inflammation, leaky gut, and immune dysfunction. This can intensify the sensitivity of the gut lining, making you more reactive to foods, stress, and environmental triggers.

Cortisol

Cortisol manages long-term stress but can disrupt digestion when chronically elevated. High cortisol slows stomach emptying and increases gut-brain signalling errors, which is common in IBS. Over time, it can contribute to both constipation-predominant and diarrhea-predominant IBS by altering gut motility and microbial balance.