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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Bloated on Mounjaro vs Wegovy — What's the Difference?
Bloating and digestive discomfort are common side effects when starting Mounjaro or Wegovy. Both medications work by slowing how quickly food leaves your stomach, which can cause temporary bloating, constipation, and gas. The experience varies between individuals — some notice bloating more with one medication than the other. This guide compares bloating risk on Mounjaro versus Wegovy, explains why it happens, and helps you understand which might suit your body better. A prescriber can assess your individual suitability 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 Cause Bloating — Mechanism Differences
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — it activates two natural hormone pathways. This dual mechanism may cause more pronounced digestive effects initially, including bloating, constipation, and nausea, particularly during dose titration as your body adjusts. Mounjaro doses range from 2.5 mg to 15 mg weekly, with each increase potentially triggering temporary bloating.
Wegovy (semaglutide) is a GLP-1-only receptor agonist — it works through a single hormone pathway. Clinical trial data from the STEP studies showed similar digestive side effects, though some users report slightly less bloating compared to Mounjaro. Wegovy titration is slower (0.25 mg up to 2.4 mg over 16+ weeks), which may allow gentler adjustment for sensitive stomachs.
Key difference: Because Mounjaro has dual action (GIP + GLP-1), it may cause more initial gastric effects. However, individual responses vary considerably — some people experience severe bloating on Wegovy but tolerate Mounjaro well, and vice versa. There is no universal "less bloating" option; prescriber assessment is essential.
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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.
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Managing Bloating and Choosing Between Them
Both medications slow gastric emptying, which typically reduces over time as your body adapts. Bloating often improves after 4–8 weeks on a stable dose. To manage symptoms: eat smaller, more frequent meals; stay hydrated; avoid high-fat and spicy foods; increase fibre gradually; and move regularly after eating.
Your prescriber will assess your medical history, current medications, and digestive sensitivity to recommend the most suitable option. Use our free GLP-1 weight loss calculator to understand projected weight loss on either medication, and our BMI calculator to track your starting point. If you experience severe, persistent bloating on either medication, contact your GP or prescriber — they may adjust your dose or suggest an alternative.
- 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 Mounjaro more likely to cause bloating than Wegovy?
Mounjaro's dual GIP+GLP-1 mechanism may cause slightly more initial digestive effects during dose titration. However, individual responses vary significantly — some people experience worse bloating on Wegovy. Clinical trials show both cause similar rates of bloating. Your prescriber can assess which suits your sensitivity better based on your health history.
How long does bloating last on Mounjaro or Wegovy?
Temporary bloating typically improves after 4–8 weeks on a stable dose as your body adapts to slowed gastric emptying. If bloating persists beyond 12 weeks or worsens, contact your GP. Staying hydrated, eating smaller meals, and avoiding high-fat foods helps during adjustment.
Can I switch from Mounjaro to Wegovy if I'm too bloated?
Yes, a switch is possible and your prescriber can manage this. Mounjaro and Wegovy have approximate dose equivalencies — for example, Mounjaro 10 mg is roughly equivalent to Wegovy 1.7 mg. However, any medication change requires prescriber guidance and reassessment of your suitability.
What's the difference between Mounjaro's dual action and Wegovy's single action?
Mounjaro activates both GIP and GLP-1 receptors (dual), while Wegovy activates GLP-1 only (single). The dual mechanism may explain slightly higher rates of nausea and bloating in early trials, but both cause similar weight loss on average. Clinical data shows both work well — choice depends on your individual tolerance.
Should I avoid both medications if I already have digestive issues?
Not necessarily, but tell your prescriber about any history of IBS, gastroparesis, or chronic bloating. They may recommend starting at a lower dose, slower titration, or suggest dietary support. Some people with sensitive stomachs tolerate one medication better than the other. Assessment is essential.
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