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 Make You Bloated?
Bloating is not listed as a common side effect of Mounjaro (tirzepatide) in UK clinical trials, though some people report mild abdominal discomfort. Both Mounjaro and Wegovy (semaglutide) can cause temporary digestive changes like nausea and constipation, which may create a sensation of fullness or mild bloating. Individual experiences vary significantly. This guide compares how these two prescription weight loss injections affect digestion and explores what the SURMOUNT and STEP clinical trial data actually showed about gastrointestinal symptoms.
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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.
Bloating and Digestive Changes: Mounjaro vs Wegovy
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist. In the SURMOUNT clinical trials, the most common gastrointestinal side effects were nausea (25–33% of participants), diarrhoea (22–23%), and constipation (22–27%). Bloating was not specifically reported as a common side effect, though abdominal discomfort or stomach pain occurred in around 11–13% of participants.
Wegovy (semaglutide), a GLP-1-only medication, showed similar patterns in STEP trials: nausea (25–40%), diarrhoea (20–23%), and constipation (16–19%). Like Mounjaro, bloating was not a highlighted side effect, though indigestion (dyspepsia) affected up to 19% of participants.
- Both medications slow gastric emptying (how quickly food leaves your stomach), which may cause sensations of fullness or mild abdominal heaviness
- Constipation can create a bloated feeling even without true bloating
- Most digestive symptoms improve within 2–4 weeks as your body adjusts
- Staying hydrated and eating small, frequent meals may help manage 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.
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Which Medication, Which Person?
Whether Mounjaro or Wegovy suits you depends entirely on your individual health profile and how your body responds to each medication. Neither medication is universally "better" for bloating—some people tolerate one far better than the other. A UK-licensed prescriber will assess your medical history, other medications, and eligibility based on your BMI and health conditions to recommend the most appropriate option. Use our free GLP-1 weight loss calculator to understand projected weight loss at different doses, and discuss any digestive concerns with your prescriber before starting. They can provide personalised guidance on managing side effects or adjusting your dose if needed.
- 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 listed side effect of Mounjaro in the UK?
Bloating is not listed as a common side effect of Mounjaro. However, nausea (25–33%), constipation (22–27%), and abdominal discomfort (11–13%) do occur in clinical trials and may create a sensation of fullness or heaviness. Most digestive symptoms resolve within 2–4 weeks as your body adjusts.
Does Wegovy cause less bloating than Mounjaro?
Clinical trial data doesn't show significant differences in bloating between Mounjaro and Wegovy. Both cause similar rates of nausea and constipation. Individual responses vary—some people tolerate one medication better than the other. Your prescriber can help determine which suits you best.
What's the difference between bloating and the fullness from these medications?
True bloating involves gas and abdominal distension. The "fullness" from Mounjaro and Wegovy is partly due to slower stomach emptying and partly psychological—these medications reduce appetite, so you feel satisfied on smaller meals. Constipation can also create a bloated sensation.
How long do digestive side effects like bloating last?
Most gastrointestinal side effects, including nausea and constipation, improve significantly within 2–4 weeks as your body adjusts. Some people experience mild symptoms throughout treatment. Staying hydrated, eating small frequent meals, and gentle physical activity can help manage discomfort.
What should I do if I experience bloating on Mounjaro?
Contact your GP or prescriber. They may recommend dose adjustment, dietary changes (smaller, more frequent meals), or temporary symptom management strategies. Never stop your medication without medical guidance. Keep a symptom diary to identify patterns and discuss with your healthcare team.
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.