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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Bloating With Mounjaro vs Wegovy — What's the Difference?
Bloating and digestive discomfort are common experiences when starting GLP-1 or dual GIP/GLP-1 weight loss injections. If you're considering Mounjaro (tirzepatide) or Wegovy (semaglutide) in the UK, understanding how these prescription medications may affect your digestion is important. Both work on appetite and stomach emptying, but they have different mechanisms. This guide compares bloating experiences with each medication to help you understand what clinical evidence shows. Your prescriber can discuss which option might suit you best after a clinical assessment.
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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.
How Mounjaro and Wegovy Affect Digestion Differently
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two hormone pathways simultaneously. This dual mechanism may contribute to digestive effects including bloating, constipation, and nausea as the body adjusts to slower stomach emptying. In the SURMOUNT clinical trials, gastrointestinal side effects were common but typically mild to moderate and often improved over time.
Wegovy (semaglutide) is a GLP-1 receptor agonist only — it activates a single hormone pathway. The STEP trials showed similar digestive side effects including bloating and constipation, though the single mechanism may produce a different symptom profile for some individuals.
- Both medications slow gastric emptying initially
- Bloating often peaks in the first 2–4 weeks after dose increases
- Individual responses vary significantly — some people experience minimal bloating, others more pronounced symptoms
- Your GLP-1 weight loss calculator can help you estimate potential outcomes, but symptom experience is individual
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If your BMI suggests you're overweight or obese, explore our GLP-1 calculators to project potential weight loss on Mounjaro or Wegovy.
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Prescriber Assessment and Individual Suitability
Neither Mounjaro nor Wegovy is universally "better" for bloating — response varies by individual. A UK prescriber will assess your medical history, existing digestive conditions, and medications to determine which is more suitable for you. If you have gastroparesis, severe IBS, or other digestive disorders, this must be disclosed during your clinical assessment, as these conditions may affect suitability.
Both medications require a prescription and clinical assessment before dispensing. Whether through NHS specialist weight management services or private online prescribing, your prescriber must evaluate your individual health profile. If bloating becomes severe or persistent, contact your GP or prescriber — they may adjust your dose or suggest management strategies.
- Staying hydrated and eating smaller, frequent meals may help with bloating
- Both medications are often used alongside reduced-calorie diet and physical activity
- Track your weight loss progress and side effects using our free progress tracker
- 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.
Does Mounjaro cause more bloating than Wegovy?
Clinical trial data shows both medications commonly cause bloating and digestive discomfort. Mounjaro's dual GIP/GLP-1 mechanism may produce a different symptom pattern for some people, but individual responses vary widely. Some people experience minimal bloating with either; others find one more tolerable than the other. Your prescriber will help determine which suits you best.
How long does bloating last when starting Mounjaro?
Bloating often occurs in the first few weeks after starting Mounjaro or increasing your dose, typically peaking around 2–4 weeks. Many people report improvement as their body adapts, though this varies individually. If bloating persists beyond 6–8 weeks or worsens, contact your GP or prescriber.
Can I take medication for bloating while on Mounjaro?
Always discuss any additional medications or over-the-counter remedies with your prescriber or GP, as some may interact with Mounjaro or slow its absorption. Your prescriber can recommend safe options. Staying hydrated and eating smaller, more frequent meals may also help manage symptoms naturally.
What's the difference between Mounjaro and Wegovy mechanisms?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist activating two hormone pathways. Wegovy (semaglutide) is a GLP-1 agonist only. This difference may affect how each medication impacts digestion, appetite, and side effects, though both slow stomach emptying. Your prescriber will choose based on your individual health profile and medical history.
Is bloating a sign Mounjaro isn't working?
No — bloating is a common, temporary side effect unrelated to weight loss effectiveness. In clinical trials (SURMOUNT), participants experienced bloating and significant weight loss simultaneously. Bloating typically improves as your body adjusts. Use your BMI calculator to track your progress objectively alongside managing side effects with your prescriber's support.
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