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 Stop Constipation on Mounjaro
Constipation is one of the most common side effects when taking Mounjaro (tirzepatide), particularly during the first few weeks of treatment. Whilst this usually improves as your body adjusts, there are several practical steps you can take to manage it and reduce discomfort. This guide covers evidence-based strategies recommended by healthcare professionals in the UK, alongside advice on when to speak to your GP if constipation becomes severe or persistent.
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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 Ease Constipation
Increase your water intake — One of the most effective strategies is drinking more water throughout the day. Aim for at least 6–8 glasses daily, though some people find they need more when taking Mounjaro. Dehydration makes constipation worse, particularly because tirzepatide slows stomach emptying.
- Drink water with meals and between meals
- Herbal tea, diluted fruit juice, and soup all count towards fluid intake
- Avoid excessive caffeine and alcohol, which can dehydrate you
Add dietary fibre gradually — Increasing soluble and insoluble fibre can help, but do this slowly to avoid bloating and gas. Include vegetables, fruit, wholegrains, and legumes in meals. Your GLP-1 weight loss calculator can help track dietary changes alongside Mounjaro treatment.
- Psyllium husk or ground flaxseed can be helpful (start with small amounts)
- Avoid sudden large increases in fibre, which may worsen symptoms initially
Increase physical activity — Movement stimulates the digestive system naturally. Even a 15–20 minute walk after meals can help reduce constipation significantly.
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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
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
When to Seek Medical Support
Most people find that constipation improves after 4–8 weeks as their body adjusts to Mounjaro. However, if constipation is severe, persistent, or causing significant discomfort, contact your GP. They may recommend a stool softener like docusate or a osmotic laxative such as lactulose or polyethylene glycol (Movicol). Avoid stimulant laxatives long-term as they can cause dependency.
Seek urgent medical attention if you experience:
- Severe abdominal pain spreading to your back (possible pancreatitis — unrelated to constipation)
- Inability to pass stools for more than 3 days with severe pain
- Signs of bowel obstruction (severe bloating, vomiting, abdominal distension)
Your prescriber or GP can adjust your Mounjaro dose or suggest alternative management strategies if constipation significantly impacts your quality of life.
- 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 a common side effect of Mounjaro?
Yes. Constipation is reported as a very common side effect, affecting more than 1 in 10 people taking Mounjaro (tirzepatide). It occurs because tirzepatide slows how food moves through the stomach and digestive tract. Most people find it improves after the first few weeks as their body adjusts to the medication.
How much water should I drink to help with Mounjaro constipation?
Aim for at least 6–8 glasses of water daily, though individual needs vary. Some people require more, particularly if they experience constipation. Drink water throughout the day with meals and between meals. Herbal tea and broth also count towards your daily fluid intake.
Can I use laxatives whilst taking Mounjaro?
Yes, but choose the right type. Stool softeners (like docusate) and osmotic laxatives (like Movicol or lactulose) are safe and effective. Avoid stimulant laxatives (like senna or bisacodyl) long-term as they can cause dependency. Always check with your GP or pharmacist before starting any new medication alongside Mounjaro.
Will constipation go away on Mounjaro, or is it permanent?
For most people, constipation improves significantly after 4–8 weeks as the body adjusts to the medication. However, some people experience mild ongoing constipation throughout treatment. Simple strategies like increased water, fibre, and movement usually manage this effectively. If it remains troublesome, speak to your GP about alternatives.
When should I contact my GP about Mounjaro constipation?
Contact your GP if constipation is severe, persists beyond 8 weeks despite trying home remedies, or significantly impacts your quality of life. Seek urgent medical attention if you experience severe abdominal pain, inability to pass stools for 3+ days with severe pain, or signs of bowel obstruction like vomiting or severe bloating.
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.