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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Does Mounjaro Cause a Bloated Stomach?
Abdominal bloating is not listed as a direct side effect of Mounjaro (tirzepatide) in UK prescribing information, but some people using this GLP-1 and GIP receptor agonist injection may experience stomach discomfort, constipation, or indigestion—which can feel like bloating. These digestive changes may occur as your body adjusts to the medication. If you're experiencing persistent bloating or stomach distension, it's important to discuss this with your GP, as it may relate to how the medication affects digestion or could indicate another health issue requiring attention.
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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.
Why Mounjaro May Cause Digestive Discomfort
Mounjaro works by slowing gastric emptying—the rate at which food moves from your stomach into your small intestine. This mechanism helps you feel fuller for longer, but it can also lead to sensations of fullness, heaviness, or bloating, especially after eating. The medication also affects how your gut processes food, which may trigger indigestion or a feeling of abdominal distension.
Common digestive side effects reported in UK clinical trials include:
- Nausea and indigestion (dyspepsia)
- Constipation or diarrhoea
- Stomach (abdominal) pain
- Loss of appetite
These effects often improve as your body adjusts over the first few weeks. However, if bloating persists or worsens, your prescriber may recommend dietary adjustments or further investigation. Remember, individual responses to tirzepatide vary significantly, and not everyone experiences these symptoms.
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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.
Managing Bloating and Stomach Discomfort
If you're experiencing bloating while taking Mounjaro, several practical steps may help:
- Eat smaller, more frequent meals instead of large portions—this reduces pressure on your stomach
- Stay hydrated with water throughout the day to support digestion
- Avoid high-fat and high-fibre foods initially, as these may worsen bloating
- Eat slowly and chew thoroughly to aid digestion
- Gentle movement such as a short walk after meals may help with gas and discomfort
If bloating continues beyond the first 4–6 weeks of treatment, or if you also experience severe stomach pain, contact your GP. They can assess whether the symptom is a normal adjustment effect or something requiring medical review. Your prescriber may also adjust your dose or provide additional support.
- 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 bloating a common side effect of Mounjaro in the UK?
Bloating is not officially listed in UK prescribing information, but digestive discomfort—including feelings of fullness, constipation, and indigestion—is common as the medication slows stomach emptying. These effects typically improve within 4–6 weeks as your body adjusts. Individual experiences vary significantly.
How does Mounjaro cause abdominal discomfort?
Mounjaro (tirzepatide) slows gastric emptying, meaning food moves more slowly through your stomach and into your small intestine. This mechanism helps reduce appetite but can cause sensations of bloating, heaviness, or fullness. The medication also affects gut hormone signalling, which may trigger indigestion.
When should I contact my GP about Mounjaro bloating?
Contact your GP if bloating persists beyond 6 weeks, severely impacts your quality of life, or is accompanied by severe stomach pain, vomiting, or other concerning symptoms. Persistent abdominal pain could indicate pancreatitis or other serious issues requiring urgent review.
Can I reduce Mounjaro bloating by changing my diet?
Yes. Eating smaller, frequent meals, staying hydrated, avoiding high-fat foods initially, and eating slowly may help. Gentle movement after meals can also ease discomfort. Your GP or prescriber can suggest dietary strategies tailored to your needs.
Is bloating a reason to stop taking Mounjaro?
Mild bloating that improves over time is usually not a reason to stop. However, if symptoms are severe, persistent, or affecting your quality of life, discuss this with your prescriber. They can assess your individual situation and advise whether continuing, adjusting the dose, or switching medication is appropriate.
Ready to take control of your weight loss journey?
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