Constipation is a common side effect when taking GLP-1 receptor agonists such as semaglutide (Ozempic, Wegovy), liraglutide (Victoza, Saxenda), dulaglutide (Trulicity), or tirzepatide (Mounjaro). These medications slow gastric emptying and reduce gut motility, leading to harder stools and difficulty passing bowel movements. Understanding why this occurs and how to manage it effectively can help you maintain comfort and continue treatment safely. This article provides practical, evidence-based strategies to support regular bowel function whilst on GLP-1 therapy, alongside guidance on when to seek medical advice.

How GLP-1 Medications Affect Bowel Movements

Glucagon-like peptide-1 (GLP-1) receptor agonists are a class of medications increasingly prescribed for type 2 diabetes management and weight loss. These include semaglutide (Ozempic, Wegovy), liraglutide (Victoza, Saxenda), and dulaglutide (Trulicity). Tirzepatide (Mounjaro) works similarly but is classified as a dual GIP/GLP-1 receptor agonist. Whilst these incretin-based therapies offer significant metabolic benefits, they commonly affect gastrointestinal function, including bowel movements.

GLP-1 receptor agonists work by mimicking the action of naturally occurring GLP-1, a hormone released from the intestine after eating. Their primary mechanisms include enhancing insulin secretion in response to glucose, suppressing glucagon release, and slowing gastric emptying. This delayed gastric emptying, alongside effects on central appetite pathways, contributes to their appetite-suppressing effects but also to gastrointestinal side effects.

The slowing of food transit through the digestive system affects the entire gastrointestinal tract, not just the stomach. As food and waste material move more slowly through the intestines, more water is absorbed from the stool, making it harder and more difficult to pass. This physiological change explains why constipation is a common adverse effect of these medications.

Gastrointestinal side effects, including constipation, nausea, and altered bowel habits, occur frequently with these medicines. The incidence varies between different products and doses, with constipation listed as 'very common' (affecting more than 1 in 10 people) with Wegovy and Saxenda, and 'common' (affecting up to 1 in 10 people) with Ozempic, Trulicity and Mounjaro. These effects are often most noticeable during dose escalation and may improve over time. Your prescriber may delay dose increases if gastrointestinal symptoms are troublesome.

Why Constipation Occurs with GLP-1 Treatment

Constipation during GLP-1 treatment results from several interconnected physiological mechanisms. The primary factor is delayed gastric emptying and reduced gastrointestinal motility throughout the digestive tract. GLP-1 receptors are present not only in the pancreas but also extensively throughout the gastrointestinal system. When these receptors are activated by GLP-1 medications, they slow the coordinated muscular contractions (peristalsis) that normally propel food and waste through the intestines.

This reduced motility means that intestinal contents remain in the colon for longer periods. The colon's primary function includes water absorption, and extended transit time allows for excessive water reabsorption from the stool. The result is harder, drier faecal matter that is more difficult to evacuate. Additionally, the appetite-suppressing effects of these medications often lead to reduced food and fluid intake, which can further contribute to constipation if adequate fibre and fluids aren't maintained.

Certain patient factors may increase susceptibility to constipation on GLP-1 therapy. These include:

• Pre-existing constipation or slow transit constipation

• Inadequate dietary fibre intake

• Insufficient fluid consumption

• Reduced physical activity levels

• Concurrent medications with constipating effects (such as opioids, certain antidepressants, or iron supplements)

• Older age, where baseline colonic motility may already be reduced

The severity of constipation often correlates with the dose of medication and may be more pronounced during dose escalation phases. Many patients experience improvement as their body adjusts to the medication, though some require ongoing management strategies. It is important to note that whilst constipation is common, it does not affect all patients, and individual responses vary considerably.

Practical Ways to Manage Constipation on GLP-1s

Effective management of constipation whilst taking GLP-1 medications involves a combination of dietary modifications, lifestyle adjustments, and, when necessary, appropriate laxative use. A stepwise approach is generally recommended, starting with conservative measures before progressing to pharmacological interventions.

Dietary fibre is fundamental to maintaining regular bowel function. Adults should aim for 30 grams of fibre daily from varied sources, as recommended by UK dietary guidelines. Soluble fibre (found in oats, beans, lentils, and fruits) helps soften stools, whilst insoluble fibre (in wholegrain bread, brown rice, and vegetables) adds bulk and promotes transit. Gradually increasing fibre intake helps prevent bloating and allows the digestive system to adjust.

Adequate hydration is equally critical. Aim for 6–8 glasses (approximately 1.5–2 litres) of fluid daily, primarily water. Increased fibre without sufficient fluid can paradoxically worsen constipation. Warm beverages, particularly in the morning, may stimulate bowel activity.

Physical activity promotes intestinal motility through mechanical stimulation and improved abdominal muscle tone. Even moderate activity such as a 30-minute daily walk can significantly improve bowel regularity.

When lifestyle measures prove insufficient, laxatives may be appropriate:

• Osmotic laxatives (macrogol/polyethylene glycol preparations) are often considered first-line for chronic constipation. They draw water into the bowel, softening stools and increasing frequency

• Bulk-forming laxatives (ispaghula husk, methylcellulose) work similarly to dietary fibre and are generally suitable for long-term use, but should be avoided if you have severe bloating or suspected impaction

• Stimulant laxatives (senna, bisacodyl) should be reserved for short-term use when other measures fail

• Rectal treatments (glycerol suppositories, small-volume enemas) can provide rapid relief for occasional constipation

Establishing a regular toilet routine can be beneficial. Allowing adequate time after meals, particularly breakfast, takes advantage of the gastrocolic reflex. Never ignore the urge to defecate, as delaying can worsen constipation. Proper positioning on the toilet—with feet elevated on a small stool to create a squatting posture—can facilitate easier evacuation.

If constipation persists despite these measures, speak to your prescriber about possibly pausing dose escalation or temporarily reducing your dose until symptoms improve.

When to Seek Medical Advice About Bowel Changes

Whilst constipation is a recognised side effect of GLP-1 medications, certain symptoms warrant prompt medical evaluation. Patients should contact their GP or prescribing clinician if they experience severe or persistent constipation that does not respond to conservative management measures within one to two weeks.

Red flag symptoms requiring urgent medical assessment include:

• Severe abdominal pain or distension, particularly if accompanied by vomiting

• Complete inability to pass stools or wind (absolute constipation), especially with pain or distension

• Rectal bleeding or blood in the stool

• Unexplained weight loss beyond that expected from the medication's therapeutic effect

• Persistent nausea and vomiting preventing adequate oral intake

• Signs of bowel obstruction, such as colicky pain, absolute constipation, and abdominal distension

• Severe persistent abdominal pain radiating to the back, which may indicate pancreatitis

• Right upper abdominal pain, fever or yellowing of the skin/eyes, which could suggest gallbladder problems

For urgent advice, contact NHS 111 or your GP. For severe symptoms, attend A&E or call 999 if appropriate.

These symptoms may indicate complications such as faecal impaction, bowel obstruction, or other serious gastrointestinal conditions requiring investigation. Whilst these medications slow gastric emptying, severe gastroparesis (stomach paralysis) is rare but has been reported and requires specialist assessment.

Patients should also seek medical review if constipation significantly impacts quality of life or if they find themselves increasingly reliant on stimulant laxatives. A healthcare professional can assess whether dose adjustment of the medication is appropriate, review concurrent medications that may contribute to constipation, and exclude other underlying causes.

For individuals with pre-existing gastrointestinal conditions such as inflammatory bowel disease, previous bowel surgery, or chronic constipation, closer monitoring may be warranted when initiating therapy. These patients should discuss their gastrointestinal history with their prescriber before starting treatment. Regular follow-up allows for early identification of problems and timely intervention.

If you experience any side effects, including constipation, you can report them directly to the MHRA Yellow Card Scheme at yellowcard.mhra.gov.uk or via the Yellow Card app.

Dietary and Lifestyle Adjustments for Regular Bowel Function

Maintaining regular bowel function whilst taking GLP-1 medications requires a proactive, holistic approach to diet and lifestyle. These adjustments not only help manage constipation but also support the overall therapeutic goals of treatment, including weight management and metabolic health.

Optimising dietary fibre intake should be gradual and balanced. High-fibre foods to incorporate include:

• Wholegrain cereals and bread (porridge, bran-based cereals, wholemeal bread)

• Pulses and legumes (lentils, chickpeas, kidney beans)

• Fruits (prunes, apples with skin, pears, berries)

• Vegetables (broccoli, carrots, Brussels sprouts, sweet potatoes)

• Nuts and seeds (almonds, linseeds, chia seeds)

Prunes and prune juice have a particularly beneficial effect due to their sorbitol content, which has a natural laxative effect. Starting with 3–4 prunes daily can be helpful.

Hydration strategies should be intentional. Keep a water bottle accessible throughout the day and establish regular drinking habits. Herbal teas and diluted fruit juices contribute to fluid intake, though excessive caffeine may have a mild diuretic effect. Monitoring urine colour (aiming for pale straw colour) provides a practical hydration indicator.

Regular physical activity need not be strenuous. The UK Chief Medical Officers recommend at least 150 minutes of moderate activity weekly. Activities that engage the core and promote general movement are beneficial. Some people find that certain yoga poses may help stimulate bowel activity, though evidence varies between individuals.

Stress management is often overlooked but important, as stress can affect gut motility. Techniques such as mindfulness, adequate sleep, and relaxation exercises support overall digestive health.

Meal timing and composition also matter. Eating regular meals, even if portions are smaller due to reduced appetite, helps maintain digestive rhythm. Including healthy fats (olive oil, avocado, oily fish) in moderation as part of a balanced diet may support overall digestive health.

Patients should maintain realistic expectations—bowel habits vary individually, and 'normal' ranges from three times daily to three times weekly. The goal is comfortable, regular evacuation without straining, rather than achieving a specific frequency. Keeping a symptom diary can help identify patterns and triggers, facilitating discussions with healthcare professionals about optimal management strategies.

Frequently Asked Questions