Constipation is a recognised gastrointestinal side effect of Mounjaro (tirzepatide), affecting approximately 6–7% of patients treated for type 2 diabetes mellitus in the UK. This GLP-1 and GIP receptor agonist slows gastric emptying to improve glycaemic control, but this mechanism can also reduce bowel motility and increase water reabsorption in the colon, leading to harder stools. Whilst generally mild to moderate and self-limiting, constipation can significantly impact quality of life if left unmanaged. Fortunately, effective relief strategies exist, ranging from dietary modifications and increased hydration to appropriate laxative use under medical guidance. Understanding how to prevent and manage this side effect enables patients to continue benefiting from Mounjaro whilst maintaining comfortable bowel function.

Understanding Constipation as a Side Effect of Mounjaro

Mounjaro (tirzepatide) is a glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) receptor agonist licensed in the UK for the treatment of type 2 diabetes mellitus. While this medication helps improve blood glucose control, gastrointestinal side effects are amongst the most commonly reported adverse reactions. Constipation affects a notable proportion of patients taking Mounjaro, though it is generally less frequent than nausea or diarrhoea.

According to the Mounjaro Summary of Product Characteristics (SmPC), constipation is classified as a common side effect, occurring in approximately 6–7% of patients receiving tirzepatide, with incidence varying according to dose. The condition is characterised by infrequent bowel movements (typically fewer than three per week), hard or lumpy stools, straining during defecation, or a sensation of incomplete evacuation. For most individuals, constipation associated with Mounjaro is mild to moderate in severity and tends to improve over time as the body adjusts to the medication.

It is important to recognise that constipation can significantly impact quality of life and, if left unmanaged, may lead to complications such as haemorrhoids, anal fissures, or faecal impaction. Understanding that this side effect is a recognised consequence of the medication's mechanism of action can help patients and healthcare professionals implement appropriate preventative and management strategies. Patients should not discontinue Mounjaro without consulting their prescribing clinician, as abrupt cessation may compromise diabetes management. If gastrointestinal side effects persist, your doctor may consider delaying dose escalation or reducing your dose. Suspected side effects can be reported via the MHRA Yellow Card scheme (yellowcard.mhra.gov.uk).

Why Mounjaro Can Cause Constipation

The constipating effect of Mounjaro relates directly to its pharmacological mechanism of action. Tirzepatide activates both GLP-1 and GIP receptors, which are incretin hormones that regulate glucose metabolism and appetite. One of the key effects of GLP-1 receptor activation is the slowing of gastric emptying—the rate at which food moves from the stomach into the small intestine. This delayed gastric emptying contributes to increased satiety and improved glycaemic control, but it also affects overall gastrointestinal motility.

When the transit of food through the digestive system is slowed, the colon has more time to absorb water from the stool. This increased water reabsorption results in harder, drier stools that are more difficult to pass. GLP-1 receptor agonists may also influence gut motility patterns, though the specific effects on colonic function are less well characterised for tirzepatide. The combined effect of delayed gastric emptying and altered gut function creates an environment conducive to constipation.

Other contributing factors may include reduced food and fluid intake secondary to the appetite-suppressing effects of Mounjaro. Patients often experience decreased hunger and earlier satiety, which can inadvertently lead to lower consumption of dietary fibre and fluids—both essential for maintaining regular bowel function. Furthermore, the dose-dependent nature of gastrointestinal side effects means that constipation may be more pronounced during dose escalation phases.

It is worth noting that the Mounjaro SmPC advises that use is not recommended in patients with severe gastrointestinal disease, such as severe gastroparesis. Understanding these mechanisms allows for targeted interventions that address the underlying causes whilst preserving the therapeutic benefits of tirzepatide treatment.

Effective Ways to Relieve Constipation While Taking Mounjaro

Managing constipation whilst taking Mounjaro requires a stepwise approach, beginning with conservative measures and progressing to pharmacological interventions if necessary. The first-line strategy involves optimising hydration and dietary fibre intake. Patients should aim to consume at least 1.5–2 litres of fluid daily (unless contraindicated by other medical conditions), with water being the preferred choice. Adequate hydration helps to soften stools and facilitate their passage through the colon.

Increasing dietary fibre intake to 25–30 grams daily can significantly improve bowel regularity. Soluble fibre sources such as oats, psyllium husk, linseeds, and fruits are particularly beneficial, as they absorb water and add bulk to stools. Insoluble fibre from vegetables, wholegrain cereals, and wheat bran also promotes intestinal transit. Fibre intake should be increased gradually to minimise bloating and gas, with concurrent increases in fluid consumption.

When dietary measures prove insufficient, osmotic laxatives like macrogol (Movicol, Laxido) are generally recommended as first-line pharmacological treatment in line with NICE Clinical Knowledge Summaries. These retain water in the bowel, softening stools without causing significant electrolyte disturbance. Bulk-forming laxatives such as ispaghula husk (Fybogel) or methylcellulose may be suitable alternatives where adequate fluid intake can be assured, but should be avoided in opioid-induced constipation or when fluid intake is poor. Note that bulk-forming laxatives should be taken at least 2 hours apart from other medications to avoid affecting their absorption.

For more resistant cases, stimulant laxatives such as senna or bisacodyl can be used, and may be appropriate for regular use under medical supervision with periodic review. Stool softeners like docusate sodium may provide additional benefit when stools are particularly hard. For acute relief of hard stools or rectal loading, glycerol suppositories or sodium citrate micro-enemas may be helpful.

Patients should consult their GP or pharmacist before commencing any laxative regimen, particularly if they have other medical conditions or take multiple medications. If constipation persists despite these measures, your prescriber may consider delaying dose escalation or reducing your Mounjaro dose. It is advisable to maintain a bowel diary to monitor frequency, consistency, and response to interventions, which can guide ongoing management decisions.

When to Seek Medical Advice About Constipation on Mounjaro

Whilst mild constipation can often be managed with self-care measures, certain circumstances warrant prompt medical evaluation. Patients should contact their GP or healthcare professional if constipation persists for more than one week despite appropriate dietary modifications and over-the-counter laxative use. Prolonged constipation may indicate the need for dose adjustment, additional investigation, or alternative management strategies.

Red flag symptoms requiring urgent medical attention include:

• Severe abdominal pain or distension that is worsening or unrelieved by simple analgesia

• Rectal bleeding, especially when accompanied by a persistent change in bowel habit

• Blood in the stool (which may appear bright red or dark and tarry)

• Unexplained weight loss beyond that expected from Mounjaro treatment

• Unexplained iron-deficiency anaemia

• Persistent nausea and vomiting, particularly if unable to tolerate oral fluids

• Severe persistent abdominal pain radiating to the back with vomiting (which may suggest pancreatitis)

• Complete inability to pass stool or wind (which may suggest bowel obstruction)

• Fever accompanying constipation, which could indicate infection or inflammation

For severe symptoms or suspected bowel obstruction, contact NHS 111, attend A&E, or call 999 in an emergency.

Patients with pre-existing gastrointestinal conditions such as inflammatory bowel disease, previous bowel surgery, or a history of intestinal obstruction should maintain particularly close communication with their healthcare team. Similarly, individuals taking other medications that may contribute to constipation (such as opioid analgesics, anticholinergic drugs, or certain antidepressants) require careful monitoring and may benefit from earlier intervention.

It is also important to seek medical advice if constipation is accompanied by new or worsening symptoms that might suggest complications, such as haemorrhoidal bleeding, anal fissures causing pain on defecation, or symptoms of faecal impaction (including overflow diarrhoea, urinary retention, or confusion in elderly patients). Healthcare professionals can assess whether constipation represents a simple side effect of Mounjaro or whether further investigation is warranted to exclude other underlying pathology. Never discontinue Mounjaro without medical guidance, as this may compromise diabetes control and potentially cause rebound hyperglycaemia.

Dietary and Lifestyle Changes to Prevent Constipation

Proactive dietary and lifestyle modifications represent the cornerstone of constipation prevention for patients taking Mounjaro. Establishing these habits from the outset of treatment can significantly reduce the likelihood of developing problematic symptoms. A structured approach to nutrition should focus on gradually increasing fibre intake through whole foods rather than relying solely on supplements. Excellent dietary sources include:

• Fruits: prunes, pears, apples (with skin), berries, and kiwifruit

• Vegetables: broccoli, Brussels sprouts, carrots, and leafy greens

• Legumes: lentils, chickpeas, kidney beans, and black beans

• Whole grains: oats, brown rice, wholemeal bread, and quinoa

• Nuts and seeds: almonds, chia seeds, and ground linseeds

It is essential to increase fibre intake gradually over 2–3 weeks to allow the digestive system to adapt and minimise bloating or discomfort. Each fibre increase should be accompanied by additional fluid intake to maximise effectiveness. NHS guidance recommends 6-8 cups of fluid daily (approximately 1.5-2 litres), though this may need adjustment for those with heart failure or kidney disease.

Regular physical activity plays a crucial role in maintaining healthy bowel function. Exercise stimulates intestinal contractions and reduces the time it takes for food to move through the large intestine. In line with UK Chief Medical Officers' guidelines, patients should aim for at least 150 minutes of moderate-intensity activity weekly, such as brisk walking, cycling, or swimming. Even gentle movement after meals, such as a short walk, can promote digestive motility.

Establishing a consistent bowel routine can also prove beneficial. Patients should respond promptly to the urge to defecate rather than delaying, as postponing bowel movements can lead to harder stools and increased difficulty passing them. Setting aside time after breakfast or another meal—when the gastrocolic reflex naturally stimulates bowel activity—can help establish regularity. Adopting a comfortable position on the toilet, with feet elevated on a small stool to create a squatting posture, can facilitate easier evacuation.

Stress management should not be overlooked, as psychological stress can significantly impact gastrointestinal function. Techniques such as mindfulness, adequate sleep, and relaxation exercises may support overall digestive health. Patients should also review their medication list with their healthcare professional to identify any other drugs that might contribute to constipation, allowing for potential adjustments where clinically appropriate. By implementing these comprehensive lifestyle strategies alongside Mounjaro treatment, patients can optimise both their diabetes management and their gastrointestinal wellbeing.

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