Diarrhoea is a common yet frequently overlooked complication in people with type 2 diabetes, affecting quality of life and glycaemic control. The causes are multifactorial, ranging from medication side effects—particularly metformin and GLP-1 receptor agonists—to diabetic autonomic neuropathy affecting bowel function. Understanding the underlying mechanisms is essential for effective management. This article explores why type 2 diabetes and diarrhoea are linked, which medications may contribute, how nerve damage affects the gut, when to seek medical advice, and practical strategies to manage symptoms whilst maintaining stable blood glucose levels.
Summary: Type 2 diabetes can cause diarrhoea through medication side effects (especially metformin and GLP-1 agonists), autonomic nerve damage affecting bowel function, altered gut bacteria, and coexisting conditions.
- Metformin, the first-line diabetes treatment, commonly causes diarrhoea through altered bile salt metabolism and changes in gut microbiota; modified-release formulations may reduce symptoms.
- Diabetic autonomic neuropathy damages nerves controlling bowel motility, leading to rapid transit times, bacterial overgrowth, and chronic watery diarrhoea (diabetic enteropathy).
- During acute diarrhoea, temporarily stop SGLT2 inhibitors and metformin, increase blood glucose and ketone monitoring, and seek medical advice to prevent diabetic ketoacidosis.
- Red flag symptoms requiring urgent GP review include persistent diarrhoea over two weeks, blood in stools, unintentional weight loss, nocturnal diarrhoea, or faecal incontinence.
- Management includes dietary modifications (avoiding artificial sweeteners, adding soluble fibre), medication review, loperamide for symptomatic relief, and optimising glycaemic control to prevent nerve damage progression.
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Why Does Type 2 Diabetes Cause Diarrhoea?
Diarrhoea is a surprisingly common yet often overlooked complication in people living with type 2 diabetes. Whilst not everyone with diabetes will experience bowel problems, chronic diarrhoea is reported in some studies, though prevalence estimates vary widely depending on definition and population studied. The relationship between type 2 diabetes and diarrhoea is multifactorial, involving several interconnected mechanisms that can disrupt normal digestive function.
The primary causes include:
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Autonomic neuropathy affecting the nerves that control bowel motility
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Medication side effects, particularly from commonly prescribed diabetes treatments
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Altered gut microbiome, which may be associated with prolonged hyperglycaemia
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Coexisting conditions such as coeliac disease (more common in type 1 diabetes but should be considered in type 2 if symptoms suggest) or pancreatic insufficiency
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Dietary factors including artificial sweeteners (sorbitol, xylitol) often used in diabetic products
Poor glycaemic control over time can damage the autonomic nervous system, which regulates involuntary bodily functions including digestion. This nerve damage, known as diabetic autonomic neuropathy, can affect the enteric nervous system—the complex network of nerves within the gastrointestinal tract. When these nerves malfunction, the normal coordinated contractions of the bowel become disrupted, potentially leading to rapid transit times and watery stools.
Additionally, chronic hyperglycaemia may contribute to bacterial overgrowth in the small intestine (SIBO), though the aetiology of SIBO is multifactorial and diagnostic certainty can be challenging. Changes in gut bacteria composition and impaired absorption of nutrients and water may also play a role. It is important to recognise that diarrhoea in diabetes is not inevitable and often has treatable underlying causes. Identifying the specific mechanism in each individual is essential for effective management and improved quality of life.
Medications for Type 2 Diabetes That May Cause Diarrhoea
Several medications commonly prescribed for type 2 diabetes can cause diarrhoea as a recognised adverse effect. Understanding which treatments are most likely to affect bowel function helps both patients and healthcare professionals anticipate and manage these symptoms effectively.
Metformin is the most frequently implicated medication. As the first-line treatment recommended by NICE for type 2 diabetes (NICE NG28), metformin affects a significant proportion of users with gastrointestinal side effects, including diarrhoea, nausea, and abdominal discomfort. The mechanism may involve altered bile salt metabolism, changes in gut microbiota, and increased intestinal secretion of fluid. These effects are typically dose-dependent and often improve over time. Starting with a low dose and gradually increasing, taking metformin with or after meals, and switching to modified-release formulations can significantly reduce gastrointestinal symptoms whilst maintaining glycaemic control.
GLP-1 receptor agonists (such as semaglutide, dulaglutide, and liraglutide) slow gastric emptying and commonly cause gastrointestinal side effects including diarrhoea, particularly during dose escalation. These injectable medications are increasingly prescribed for their cardiovascular and weight-loss benefits, but gastrointestinal side effects are among the most common reasons for discontinuation. Slow dose titration may help reduce these effects.
SGLT2 inhibitors (including dapagliflozin, empagliflozin, and canagliflozin) work by increasing urinary glucose excretion. Diarrhoea is not a typical class adverse effect according to UK Summaries of Product Characteristics. Alpha-glucosidase inhibitors (acarbose) delay carbohydrate absorption and frequently cause flatulence, bloating, and diarrhoea due to undigested carbohydrates reaching the colon.
Important sick-day advice: During acute diarrhoea or dehydrating illness, you should temporarily stop SGLT2 inhibitors and metformin and seek advice from your GP or diabetes team. If you are taking an SGLT2 inhibitor, check your blood ketones even if your glucose is normal, as these medicines can rarely cause diabetic ketoacidosis during illness.
If you suspect your diabetes medication is causing persistent diarrhoea, do not stop treatment without consulting your GP or diabetes specialist. Alternative medications or formulations may be available that provide effective glucose control with fewer gastrointestinal effects. If you experience a suspected side effect from any medicine, you can report it via the MHRA Yellow Card scheme at yellowcard.mhra.gov.uk.
Diabetic Enteropathy: When Nerve Damage Affects the Bowel
Diabetic enteropathy represents a specific complication of long-standing diabetes where autonomic neuropathy affects the gastrointestinal tract. This condition can manifest with a range of symptoms, including chronic or intermittent diarrhoea, constipation (or alternating patterns), faecal incontinence, abdominal pain, and bloating. The prevalence increases with diabetes duration and is more common in those with poor long-term glycaemic control.
The pathophysiology of diabetic enteropathy is complex. Damage to the autonomic nerves disrupts the coordinated muscular contractions (peristalsis) that normally propel food through the digestive system. In the small intestine, this can lead to bacterial overgrowth (SIBO), as stagnant contents provide an environment for excessive bacterial proliferation. These bacteria ferment undigested food, producing gas and organic acids that draw water into the bowel lumen, resulting in watery diarrhoea. Additionally, bile acid diarrhoea—where unabsorbed bile acids irritate the colon—is a recognised cause of chronic watery diarrhoea and may occur through various mechanisms.
Diabetic diarrhoea specifically refers to chronic, watery diarrhoea occurring predominantly at night or after meals, often accompanied by faecal urgency or incontinence. This can be profoundly distressing and significantly impact quality of life, yet it remains underdiagnosed and undertreated.
Diagnosis typically involves excluding other causes of chronic diarrhoea through appropriate investigations, which may include blood tests (full blood count, urea and electrolytes, liver function tests, C-reactive protein, coeliac serology with total IgA, thyroid function), stool samples (microscopy, culture, ova and parasites, Clostridioides difficile toxin if recent antibiotic use), faecal calprotectin (to assess for inflammatory bowel disease), and stool elastase (if pancreatic insufficiency is suspected). Depending on symptoms and age, a faecal immunochemical test (FIT) may be indicated. Breath testing for SIBO has limitations and variable availability; empirical antibiotic therapy may be considered under specialist guidance. Where bile acid diarrhoea is suspected, SeHCAT testing (where available) or an empirical trial of a bile acid sequestrant may be appropriate per BSG guidance.
Management focuses on optimising glycaemic control to prevent further nerve damage, treating bacterial overgrowth with antibiotics when present (noting that rifaximin for SIBO is an unlicensed indication and antimicrobial stewardship should be observed), and using antidiarrhoeal medications such as loperamide as first-line symptomatic therapy. Codeine phosphate or co-phenotrope may be considered under specialist advice for short-term use, with caution due to sedation and misuse potential. Dietary modifications, including soluble fibre supplementation, may also provide symptomatic relief.
When to See Your GP About Diarrhoea with Type 2 Diabetes
Whilst occasional loose stools may not require immediate medical attention, certain features warrant prompt evaluation by your GP or diabetes care team. Recognising these 'red flag' symptoms ensures that serious underlying conditions are not missed and that appropriate investigations are undertaken.
You should contact your GP if you experience:
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Persistent diarrhoea lasting more than two weeks without obvious cause
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Blood in your stools (visible red blood or black, tarry stools)
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Unintentional weight loss accompanying bowel changes
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Severe abdominal pain or cramping
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Fever or signs of systemic infection
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Nocturnal diarrhoea that regularly wakes you from sleep
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Faecal incontinence affecting your daily activities
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Signs of dehydration including dizziness, reduced urination, or confusion
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Change in bowel habit if you are aged 60 or over
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Iron-deficiency anaemia or a rectal mass on examination
It is particularly important to seek medical advice if diarrhoea is affecting your ability to take your diabetes medications or maintain adequate nutrition and hydration. Acute diarrhoeal illnesses can rapidly destabilise blood glucose control and increase the risk of diabetic ketoacidosis or hyperosmolar hyperglycaemic state, particularly if you are unable to eat or drink normally.
Sick-day rules: During acute diarrhoea or dehydrating illness, you should temporarily stop SGLT2 inhibitors and metformin. If you take an SGLT2 inhibitor, check your blood ketones even if your glucose is normal, and seek urgent medical advice if you develop nausea, vomiting, or abdominal pain. Increase your blood glucose and ketone monitoring and contact your diabetes team for guidance.
Your GP will take a detailed history, including the duration and pattern of symptoms, associated features, current medications, and dietary habits. Examination and initial investigations typically include blood tests (full blood count, urea and electrolytes, liver function tests, C-reactive protein, coeliac serology with total IgA, thyroid function, HbA1c), stool samples (microscopy, culture, ova and parasites, Clostridioides difficile toxin if recent antibiotic use), faecal calprotectin, and where indicated faecal immunochemical test (FIT) and stool elastase. Assessment of hydration status is also important.
Depending on findings and in line with NICE guidance (NG12), your GP may refer you urgently (two-week wait) if certain features are present, adjust your diabetes medications, prescribe symptomatic treatment, or refer you to gastroenterology for specialist assessment and further investigations such as colonoscopy. Early evaluation ensures that treatable causes are identified and that your diabetes management is optimised during this period.
Managing Diarrhoea While Controlling Your Blood Sugar
Balancing effective diarrhoea management with optimal glycaemic control requires a comprehensive approach addressing both symptoms and underlying causes. The following strategies can help you manage bowel symptoms whilst maintaining stable blood glucose levels.
Dietary modifications form the cornerstone of management. Keeping a food and symptom diary can help identify specific triggers. Consider reducing intake of artificial sweeteners (sorbitol, xylitol, mannitol), caffeine, alcohol, and high-fat foods, all of which can exacerbate diarrhoea. Soluble fibre supplements such as psyllium husk or methylcellulose can help bulk stools and slow transit time. Probiotic supplements may benefit some individuals by restoring healthy gut microbiota, though evidence remains mixed.
Medication review is essential. If you suspect your diabetes medication is contributing to symptoms, discuss alternatives with your healthcare team. Modified-release metformin formulations cause fewer gastrointestinal side effects than standard preparations. Taking metformin with or after meals, gradual dose titration, and splitting doses can also help. Dose adjustments or switching to different drug classes may be appropriate whilst maintaining glycaemic targets.
Symptomatic treatment with antidiarrhoeal agents such as loperamide (first-line) can provide relief for acute episodes or when symptoms significantly impact daily activities. However, these should be used judiciously and under medical supervision, particularly if infection has not been excluded. Codeine phosphate or co-phenotrope may be considered under specialist advice for short-term use, with caution due to sedation and misuse potential. For diabetic enteropathy with proven or strongly suspected bacterial overgrowth, courses of antibiotics may be prescribed under specialist guidance, noting that rifaximin for SIBO is an unlicensed indication and antimicrobial stewardship should be observed. Where bile acid diarrhoea is confirmed (e.g., by SeHCAT testing) or strongly suspected, bile acid sequestrants such as colestyramine or colesevelam may be helpful.
Glycaemic control itself is therapeutic. Maintaining HbA1c within your individualised target range—typically 48 mmol/mol for most people on treatments that do not cause hypoglycaemia, or 53 mmol/mol if on therapies associated with hypoglycaemia risk, as per NICE NG28—can prevent progression of autonomic neuropathy and reduce the risk of further complications. Your diabetes team will agree a personalised target with you.
Hydration and electrolyte balance are crucial, particularly during acute diarrhoeal episodes. Oral rehydration solutions can help maintain fluid and electrolyte balance. Monitor your blood glucose more frequently during illness, as dehydration and stress can cause unpredictable fluctuations. Remember to follow sick-day rules: temporarily stop SGLT2 inhibitors and metformin during acute dehydrating illness, increase glucose and ketone monitoring, and seek clinical advice.
If you experience a suspected side effect from any medicine, you can report it via the MHRA Yellow Card scheme at yellowcard.mhra.gov.uk. Maintain open communication with your diabetes care team. Regular review allows for treatment optimisation and ensures that new or worsening symptoms are promptly addressed. With appropriate management, most people with type 2 diabetes and diarrhoea can achieve good symptom control whilst maintaining effective glucose management.
Frequently Asked Questions
Why does my diabetes medication give me diarrhoea?
Metformin, the most commonly prescribed diabetes medication, causes diarrhoea in many users by altering bile salt metabolism, changing gut bacteria, and increasing intestinal fluid secretion. GLP-1 receptor agonists like semaglutide slow gastric emptying and commonly cause gastrointestinal side effects during dose escalation. Modified-release metformin formulations, taking medication with meals, and gradual dose titration can significantly reduce these symptoms whilst maintaining blood sugar control.
Can type 2 diabetes cause diarrhoea even without medication?
Yes, long-standing diabetes can damage the autonomic nerves controlling bowel function, a condition called diabetic enteropathy. This nerve damage disrupts normal intestinal contractions, leading to bacterial overgrowth, rapid transit times, and chronic watery diarrhoea that often occurs at night or after meals. Poor glycaemic control over time increases the risk of developing this complication.
What should I do if I have diarrhoea and take SGLT2 inhibitors?
Temporarily stop your SGLT2 inhibitor (such as dapagliflozin or empagliflozin) during acute diarrhoea or dehydrating illness, and also stop metformin if you take it. Check your blood ketones even if your glucose is normal, as SGLT2 inhibitors can rarely cause diabetic ketoacidosis during illness. Increase your blood glucose and ketone monitoring, maintain hydration, and contact your GP or diabetes team for guidance.
When should I see my GP about diarrhoea with type 2 diabetes?
Contact your GP if diarrhoea persists for more than two weeks, you notice blood in your stools, experience unintentional weight loss, have severe abdominal pain, develop nocturnal diarrhoea that wakes you from sleep, or experience faecal incontinence. These red flag symptoms require prompt evaluation to exclude serious underlying conditions and ensure appropriate investigations are undertaken.
Is there a difference between diarrhoea from metformin and diabetic nerve damage?
Yes, metformin-related diarrhoea typically occurs soon after starting or increasing the dose, is often dose-dependent, and improves over time or with modified-release formulations. Diabetic enteropathy from nerve damage develops gradually over years of poor glycaemic control, causes chronic watery diarrhoea often at night or after meals, and may be accompanied by faecal urgency or incontinence. Your GP can help distinguish between these causes through clinical assessment and medication review.
Can I take loperamide for diarrhoea if I have diabetes?
Yes, loperamide is the first-line antidiarrhoeal treatment and can be used safely in people with diabetes for acute episodes or when symptoms significantly impact daily activities. However, it should be used judiciously and under medical supervision, particularly if infection has not been excluded. Maintain adequate hydration, monitor your blood glucose more frequently during diarrhoeal illness, and follow sick-day rules by temporarily stopping SGLT2 inhibitors and metformin.
The health-related content published on this site is based on credible scientific sources and is periodically reviewed to ensure accuracy and relevance. Although we aim to reflect the most current medical knowledge, the material is meant for general education and awareness only.
The information on this site is not a substitute for professional medical advice. For any health concerns, please speak with a qualified medical professional. By using this information, you acknowledge responsibility for any decisions made and understand we are not liable for any consequences that may result.
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