The UK's most complete GLP-1 guide
Every Question Answered. Every Side Effect Explained.
- How GLP-1 medications work
- Mounjaro vs Wegovy compared
- Injection instructions
- Side effects & solutions
- What to eat on treatment
- FAQs answered
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How to Help Constipation When Taking Mounjaro
Constipation is one of the most frequently reported side effects when starting Mounjaro (tirzepatide), but there are practical steps you can take to manage it. Mounjaro works by slowing how quickly food moves through your digestive system, which can contribute to constipation, particularly in the first few weeks of treatment. Most people find that symptoms improve as their body adjusts to the medication. This guide explains evidence-based strategies to help ease constipation while taking Mounjaro, when to seek GP support, and what to expect as you continue your treatment.
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Enter your height and weight below. Supports both imperial (stone & lbs) and metric (kg). Results include NHS category, healthy weight range, and ethnicity adjustments.
What Is BMI and Why Does It Matter?
Body Mass Index (BMI) is the most widely used screening tool for assessing whether your weight falls within a healthy range. Used by the NHS, GPs, and weight management services across the UK, BMI provides a quick snapshot of your weight relative to your height. The formula is simple: your weight in kilograms divided by your height in metres squared (kg/m²).
While BMI isn't a perfect measure — it doesn't account for muscle mass, bone density, or fat distribution — it remains the standard first step in identifying potential weight-related health risks including type 2 diabetes, cardiovascular disease, high blood pressure, and certain cancers.
The NHS also recommends adjusted thresholds for people of South Asian, Chinese, or Black African heritage — a BMI of 23 or above is classified as overweight, and 27.5 as obese. Our calculator includes this adjustment as a one-click toggle.
Practical Strategies to Relieve Constipation on Mounjaro
Managing constipation on Mounjaro involves simple lifestyle adjustments that work alongside your prescription:
- Increase water intake — Aim for at least 2–3 litres of water daily. Dehydration is a major contributor to constipation, and Mounjaro can reduce appetite, making it easy to forget to drink enough. Keep water with you throughout the day.
- Add dietary fibre gradually — Include more vegetables, fruits, whole grains, and legumes in your meals. Increase fibre slowly over a few days to avoid bloating or worsening symptoms. High-fibre foods help bulk up stool and stimulate bowel movement.
- Gentle physical activity — Walking, swimming, or light exercise can help stimulate digestion and bowel movements. Even 15–20 minutes of daily movement can make a noticeable difference.
- Use the toilet regularly — Don't ignore the urge to go. Establish a routine, ideally after meals when your digestive system is naturally more active.
- Stool softeners or osmotic laxatives — Products like docusate or polyethylene glycol (movicol) can help without overstimulating your bowel. Ask your pharmacist or GP which option is suitable for you.
These strategies work best when combined together rather than used in isolation.
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How It Works
Three simple steps to understand your weight and take action.
Enter your height and weight in our free calculator. Get your BMI, NHS category, healthy weight range, and ethnicity-adjusted thresholds instantly.
If your BMI suggests you're overweight or obese, explore our GLP-1 calculators to project potential weight loss on Mounjaro or Wegovy.
Use our progress tracker to log your weight weekly, visualise your journey with charts, and stay motivated — all stored privately in your browser.
Free Weight Loss Tools & Guides
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When to Contact Your GP and What to Expect
Constipation usually improves within the first 4–8 weeks as your body adjusts to Mounjaro's effects on digestion. Contact your GP if constipation is severe, persistent beyond 8 weeks, accompanied by abdominal pain, or if you've had no bowel movement for more than 3 days. Your GP may recommend prescription laxatives or adjust your dose timing. Rarely, constipation combined with severe stomach pain could indicate pancreatitis — seek urgent medical attention if this occurs. Remember that your prescriber needs to know about ongoing side effects: they can offer additional support or, in some cases, consider whether dose adjustments might help. Constipation alone is rarely a reason to stop Mounjaro, but your individual situation matters.
- Dual GIP/GLP-1 receptor agonist
- Up to 22.5% body weight loss (SURMOUNT-1)
- Weekly injection, dose escalation over 20+ weeks
- Available via private prescription in the UK
- Doses: 2.5mg → 5mg → 7.5mg → 10mg → 12.5mg → 15mg
- GLP-1 receptor agonist
- Up to 15–17% body weight loss (STEP trials)
- Weekly injection, 5-step dose escalation
- NHS & private prescription available
- Doses: 0.25mg → 0.5mg → 1mg → 1.7mg → 2.4mg
Mounjaro vs Wegovy: Head-to-Head
A side-by-side comparison of the two most popular GLP-1 weight loss medications available in the UK.
| Feature | Mounjaro | Wegovy |
|---|---|---|
| Drug class | Dual GIP/GLP-1 agonist | GLP-1 agonist |
| Active ingredient | Tirzepatide | Semaglutide |
| Avg. weight loss | 15–22.5% | 12–17% |
| Key trial | SURMOUNT-1 (2022) | STEP 1 (2021) |
| Max dose | 15 mg weekly | 2.4 mg weekly |
| Escalation period | 20–32 weeks | 16–20 weeks |
| Administration | Weekly injection (pen) | Weekly injection (pen) |
| NHS availability | Private prescription only | NHS & private |
| Approx. private cost | £150–£250/month | £150–£300/month |
| Common side effects | Nausea, diarrhoea, constipation | Nausea, vomiting, diarrhoea |
Data sourced from SURMOUNT-1 and STEP 1 clinical trials. Costs are approximate and vary by provider. Always consult a prescriber.
Am I Eligible for Weight Loss Medication?
In the UK, eligibility for GLP-1 weight loss medications like Mounjaro and Wegovy is based on your BMI and overall health profile.
- BMI of 30 or above (obese)
- Age 18 or over
- No contraindicated conditions
- Committed to lifestyle changes
- BMI of 27 or above
- Plus type 2 diabetes
- Or high blood pressure
- Or obstructive sleep apnoea
Use our BMI calculator to check whether your BMI falls within the eligible range.
How We Built These Tools
Every calculator and guide on myweightcheck is built with accuracy and transparency in mind. Our BMI calculator uses the standard WHO formula with NHS-aligned category thresholds. Our GLP-1 projections are modelled on published clinical trial data from SURMOUNT and STEP studies.
All data stays on your device. We don't require sign-ups, and we don't store your health information on any server. Your progress tracker saves data locally in your browser using localStorage, so only you can see it.
We're based in the UK and our tools are designed specifically for UK users — supporting stone & lbs by default, referencing NHS guidelines, using NICE-approved medication data, and linking to GPhC-registered pharmacies.
Frequently Asked Questions
Common questions about BMI, weight loss medications, and our free UK tools.
Is constipation common on Mounjaro?
Yes, constipation is one of the most frequently reported side effects, affecting up to 1 in 10 people. It's more likely in the first few weeks as your body adjusts to how the medication slows digestion. Most people find symptoms improve significantly over time with lifestyle adjustments.
How does Mounjaro cause constipation?
Mounjaro (tirzepatide) slows gastric emptying — how quickly food leaves your stomach and moves through your digestive system. This effect typically reduces over time. Additionally, Mounjaro reduces appetite, which can mean consuming less fibre and fluids if you're not intentional about intake, contributing to constipation.
Should I stop taking Mounjaro if I have constipation?
No — constipation alone is not a reason to stop Mounjaro. It's a manageable side effect that improves in most people within weeks. Speak to your GP or prescriber about strategies to manage it. Only stop if advised by your healthcare provider, usually due to a more serious complication.
Are there medicines I can safely take for constipation while on Mounjaro?
Yes. Osmotic laxatives like polyethylene glycol (Movicol) and stool softeners like docusate are safe and often recommended. Stimulant laxatives are usually a second-line option. Always inform your pharmacist or GP that you're taking Mounjaro, as it may affect how other medications are absorbed.
How can I track whether my constipation is improving?
Keep a simple record of bowel movements and stool consistency over 2–4 weeks. You can also log general wellbeing and side effects using our free progress tracker to monitor how you're adjusting to Mounjaro overall. This helps you and your GP assess whether current strategies are working.
Ready to take control of your weight loss journey?
Start with a free BMI check, explore your GLP-1 options, or begin tracking your progress today. No sign-up. No cost. Just results.