Constipation is a common side effect of GLP-1 receptor agonists such as semaglutide (Ozempic, Wegovy), dulaglutide (Trulicity), and liraglutide (Victoza, Saxenda), affecting up to 24% of patients. These medications slow gastric emptying to promote satiety and weight loss, but this mechanism can disrupt normal bowel function. Choosing the best laxative for GLP-1 patients requires understanding individual symptoms, stool consistency, and medical history. This guide reviews evidence-based laxative options available in the UK, lifestyle modifications to support bowel health, and when to seek medical advice for constipation during GLP-1 therapy.

Why GLP-1 Medications Cause Constipation

Glucagon-like peptide-1 (GLP-1) receptor agonists, including semaglutide (Ozempic, Wegovy), dulaglutide (Trulicity), and liraglutide (Victoza, Saxenda), are increasingly prescribed for type 2 diabetes management and weight loss. These medications work by mimicking the action of naturally occurring GLP-1 hormones, which regulate blood glucose levels and appetite. However, their mechanism of action affects gastrointestinal motility, making constipation a commonly reported adverse effect.

GLP-1 receptor agonists slow gastric emptying—the rate at which food moves from the stomach into the small intestine. This delayed transit helps patients feel fuller for longer, contributing to reduced calorie intake and weight loss. This slowing of gastric emptying and possibly slower intestinal transit can contribute to constipation. The frequency of constipation varies by medication and dose; for example, clinical trials show constipation occurs in approximately 24% of patients taking Wegovy (semaglutide 2.4mg), with lower rates typically seen with dulaglutide and standard-dose semaglutide.

The severity of constipation varies considerably among individuals. Some patients notice mild changes in bowel habits, whilst others develop significant discomfort. Gastrointestinal side effects are most common during dose escalation and may improve with slower titration or temporary interruption of treatment. Risk factors for more severe constipation include pre-existing bowel conditions, inadequate fluid intake, low dietary fibre, reduced physical activity, and concurrent use of other constipating medications such as opioids or certain antidepressants.

Understanding this pharmacological effect is essential for both patients and healthcare professionals. Constipation related to GLP-1 therapy is not a sign of treatment failure but rather a predictable consequence of the medication's mechanism. With appropriate management strategies, most patients can continue their GLP-1 treatment whilst maintaining comfortable bowel function.

Best Laxatives for GLP-1 Patients in the UK

When lifestyle modifications prove insufficient, laxatives can provide effective relief for GLP-1-related constipation. The choice of laxative should be individualised based on symptom severity, stool consistency, patient preference, and any co-existing medical conditions. In the UK, several evidence-based options are available over the counter or on prescription.

Osmotic laxatives such as macrogol (Movicol, Laxido) draw water into the bowel, softening stools and promoting evacuation. They are well-tolerated for extended periods and are often preferred as first-line treatment for chronic constipation, particularly when bloating or nausea are prominent symptoms. Lactulose, another osmotic agent, may cause bloating and flatulence, which some patients find uncomfortable alongside GLP-1-related gastrointestinal effects.

Bulk-forming laxatives such as ispaghula husk (Fybogel) or sterculia (Normacol) work by absorbing water in the intestine, increasing stool bulk and stimulating natural peristalsis. They are suitable for long-term use and align well with the chronic nature of GLP-1 therapy. Patients must ensure adequate fluid intake when using bulk-forming laxatives to prevent intestinal obstruction. These should be avoided in patients with suspected obstruction, significant dysphagia, or severe gastroparesis symptoms. Effects typically develop within 12 to 72 hours.

Stimulant laxatives such as senna or bisacodyl should be reserved for occasional use rather than daily management. Whilst effective within 6 to 12 hours, prolonged unsupervised use is not recommended. They can be useful for breakthrough constipation but should be used under medical supervision if needed long-term.

Stool softeners like docusate sodium have limited evidence supporting their efficacy as monotherapy but may be combined with other laxatives. Some clinicians recommend starting with macrogol or a bulk-forming laxative and adding a stimulant only if needed. For rapid relief, glycerol suppositories may be considered.

Always consult your GP or pharmacist before starting any laxative regimen, particularly if you have inflammatory bowel disease, intestinal obstruction, severe abdominal pain, or are pregnant or breastfeeding. If you have heart failure or kidney disease, discuss appropriate fluid intake targets with your healthcare provider.

When to Seek Medical Advice About Constipation

Whilst constipation is a common and generally manageable side effect of GLP-1 therapy, certain symptoms warrant prompt medical evaluation. Patients should contact their GP or healthcare provider if they experience no bowel movement for more than seven days despite using laxatives, as this may indicate severe constipation or faecal impaction requiring medical intervention.

Severe abdominal pain, particularly if accompanied by vomiting, abdominal distension, or inability to pass wind, requires urgent assessment. These symptoms could indicate bowel obstruction, a rare but serious complication. If symptoms are severe or come on suddenly, call NHS 111 for urgent advice or 999 in an emergency.

Rectal bleeding or the passage of black, tarry stools should never be ignored, as these may signal underlying pathology unrelated to GLP-1 medication. This is particularly important if you are aged 50 or over. Similarly, a change in bowel habit lasting more than 6 weeks in people aged 60 or over should be discussed with your GP, who may arrange tests such as a full blood count or faecal immunochemical test (FIT).

Patients should also seek advice if they notice unexplained weight loss (beyond that expected from GLP-1 therapy), especially if you are 40 or over and have abdominal pain. Persistent nausea and vomiting that prevents adequate fluid intake, or symptoms of dehydration such as dizziness, reduced urine output, or dark-coloured urine also warrant medical attention. In these cases, your doctor may consider adjusting your GLP-1 dose or temporarily interrupting treatment.

If over-the-counter laxatives provide no relief after one week of appropriate use, or if you find yourself requiring increasing doses or multiple laxative types, medical review is advisable. Your GP can assess for complications, review your medication regimen for other constipating agents, and consider whether dose adjustment of your GLP-1 medication might be appropriate. In some cases, referral to a gastroenterologist may be necessary for specialist assessment and management.

If you suspect your constipation is a side effect of your medication, you can report this through the MHRA Yellow Card scheme (yellowcard.mhra.gov.uk or the Yellow Card app).

Lifestyle Changes to Support Bowel Health on GLP-1 Treatment

Implementing evidence-based lifestyle modifications can significantly reduce constipation severity in patients taking GLP-1 medications, and these strategies should form the foundation of management before escalating to pharmacological interventions.

Adequate hydration is paramount. Patients should aim for 2 to 2.5 litres of fluid daily, primarily from water, unless advised otherwise by your healthcare provider due to heart or kidney conditions. GLP-1 medications reduce appetite, which may inadvertently decrease fluid intake. Setting regular reminders or keeping a water bottle accessible can help maintain hydration. While caffeinated drinks do contribute to fluid intake, water is preferable. Alcohol should be limited as it can contribute to dehydration.

Dietary fibre intake should be gradually increased to 30 grams daily, in line with UK recommendations. Excellent sources include wholegrain cereals, brown rice, wholemeal bread, fruits (particularly prunes, pears, and apples with skin), vegetables, pulses, and nuts. Introduce fibre slowly over several weeks to minimise bloating and gas, which can be problematic alongside GLP-1-related gastrointestinal effects. Prunes and prune juice contain sorbitol, a natural laxative, and may be particularly beneficial.

Regular physical activity stimulates intestinal motility and promotes regular bowel movements. The UK Chief Medical Officers' guidelines recommend at least 150 minutes of moderate-intensity activity weekly for general health. Even gentle walking for 20–30 minutes daily can improve bowel function. Patients should discuss appropriate exercise levels with their healthcare provider, particularly if they have cardiovascular conditions or mobility limitations.

Establishing a bowel routine can be helpful. Allocating time after meals—when the gastrocolic reflex naturally stimulates bowel activity—and responding promptly to the urge to defaecate prevents stool from becoming harder and more difficult to pass. Avoid straining, as this can lead to haemorrhoids and anal fissures.

Medication review is essential. Discuss all medications and supplements with your GP or pharmacist, as many commonly prescribed drugs (including certain antihypertensives, antidepressants, iron supplements, and opioid analgesics) can worsen constipation. In some cases, alternatives may be available. Probiotics have limited evidence for treating GLP-1-related constipation, though they are generally safe and may benefit some individuals. These lifestyle interventions work synergistically with laxatives when needed and support long-term bowel health throughout GLP-1 treatment.

Frequently Asked Questions