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
Free tracker included with every download this week
Mounjaro Bloating vs Wegovy — What's the Difference?
Both Mounjaro and Wegovy are prescription-only weight loss injections available in the UK, but they work differently and may cause different side effects. Bloating and digestive discomfort are common experiences with both medications during the initial weeks of treatment. Understanding how these medicines compare can help you and your prescriber decide which might be more suitable for your health profile. This guide explains the mechanisms, clinical trial evidence, and individual variation to help you make an informed decision with your GP or healthcare provider.
10,000+ calculations today · NHS-aligned thresholds · 100% free
Calculate Your BMI Instantly
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.
How Mounjaro and Wegovy Differ — The Science Behind Bloating
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two natural hormone pathways in the body. This dual mechanism may affect how the stomach empties and how food moves through the digestive tract, potentially contributing to bloating and abdominal discomfort. In the SURMOUNT-1 clinical trial, bloating and stomach symptoms were reported by a significant proportion of participants, particularly in the first 4–8 weeks as the body adjusted to the medication.
Wegovy (semaglutide) is a single GLP-1 receptor agonist, activating only one hormone pathway. This single mechanism may result in a different side effect profile compared to Mounjaro. In STEP clinical trials, nausea and gastrointestinal symptoms were common, though the pattern and duration sometimes differed from dual-action medications.
- Mounjaro: dual action (GIP + GLP-1) — may slow gastric emptying more significantly
- Wegovy: single action (GLP-1 only) — different mechanism may mean different bloating patterns
- Both: bloating typically improves as your body adjusts over weeks 4–12
- Individual variation is significant — some people experience minimal bloating, others more noticeable symptoms
Your prescriber will assess which medication suits your individual digestive health and medical history.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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 Choosing Between Them — Individual Suitability
Neither Mounjaro nor Wegovy is assured to cause bloating — symptoms vary widely between individuals. Some people tolerate one medication much better than the other, while others experience similar side effects with both. Your prescriber will consider your medical history, any existing digestive conditions (like irritable bowel syndrome or gastroparesis), and current medications when deciding which is most appropriate.
If you experience significant bloating on either medication, your GP can adjust your dose or discuss alternative options. It's also important to follow dietary guidance — eating slowly, in smaller portions, and avoiding high-fat foods can help reduce bloating alongside GLP-1 or GIP/GLP-1 treatment. Use our free GLP-1 weight loss calculator to explore potential outcomes with either medication, and discuss your bloating concerns with your prescriber before starting treatment.
- 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 can cause bloating, but individual responses vary significantly. Mounjaro's dual mechanism may affect stomach emptying differently than Wegovy's single mechanism, but this doesn't mean one is universally worse. Your prescriber will assess which is more suitable based on your medical history and digestive health.
How long does Mounjaro bloating last?
Bloating typically improves as your body adjusts to Mounjaro over the first 4–12 weeks. Most people find symptoms reduce significantly by weeks 8–12, though some experience persistent mild bloating. Eating smaller, slower meals and staying hydrated can help. If bloating remains severe, discuss with your GP about dose adjustments.
Can I switch from Mounjaro to Wegovy if I have bloating?
Yes, switching is possible with your prescriber's guidance. However, any switch between medications requires clinical assessment and careful planning. Your GP will ensure the transition is safe and monitor your response to the new medication. Never stop or switch medications without consulting your prescriber.
What's the difference between tirzepatide and semaglutide?
Tirzepatide (Mounjaro) activates two hormone receptors — GIP and GLP-1 — while semaglutide (Wegovy) activates GLP-1 only. This dual versus single mechanism means they work slightly differently in the body, which can affect both effectiveness and side effects. Both require a prescription and clinical assessment in the UK.
Is bloating a sign that Mounjaro or Wegovy is working?
No. Bloating is a side effect that's unrelated to weight loss effectiveness. Some people lose weight without experiencing significant bloating, while others may experience bloating but lose weight effectively. Bloating typically decreases over time as your body adjusts, independent of how well the medication is supporting your weight loss.
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.