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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Why Am I Feeling Bloated on Mounjaro?
Feeling bloated on Mounjaro (tirzepatide) is a common experience, particularly during the early weeks of treatment or when your dose increases. Bloating and abdominal discomfort can occur because Mounjaro slows how quickly food moves through your digestive system and reduces your appetite, which may cause your stomach to feel fuller or more distended. This is a recognised side effect, though it typically improves as your body adjusts to the medication. Understanding why it happens and what you can do about it may help you manage this symptom more effectively.
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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.
Common Causes of Bloating on Mounjaro
Bloating on Mounjaro happens due to several mechanisms. The medication slows gastric emptying — the rate at which food leaves your stomach — which can make your stomach feel fuller and more distended, especially after meals. Additionally, Mounjaro reduces your appetite, so you may eat smaller portions; if you then eat normal-sized meals, your digestive system may struggle to process the food efficiently. You might also experience constipation or indigestion, both listed as common side effects, which contribute to that heavy, bloated feeling.
- Slower stomach emptying (gastric slowdown)
- Reduced appetite meaning you may struggle with normal meal sizes
- Constipation, which traps gas and causes abdominal distension
- Indigestion and acid reflux, which may create bloating sensations
- Eating too quickly or not chewing properly (common when appetite returns)
Bloating is most common in the first 4–8 weeks of treatment or after a dose increase. Most people find it improves significantly as their body adjusts, typically within 2–4 weeks of adjustment. If you're experiencing severe or persistent bloating, always contact your GP or the healthcare professional managing your Mounjaro treatment.
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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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How to Manage Bloating While on Mounjaro
If you're bloated on Mounjaro, several practical steps may help. Eat smaller, more frequent meals rather than three large meals — this is easier for your slowed digestive system to process. Chew food thoroughly and eat slowly, giving your stomach time to signal fullness. Stay well hydrated with water (not fizzy drinks), increase fibre gradually (not suddenly, which can worsen bloating), and avoid foods known to cause gas, such as beans, cruciferous vegetables, and carbonated beverages.
- Eat 4–6 smaller meals instead of 3 large ones
- Chew thoroughly and eat slowly — aim for 20+ minutes per meal
- Drink plain water; avoid fizzy or sugary drinks
- Gentle walking after meals aids digestion
- Keep a food diary to identify trigger foods
- Consider ginger tea or peppermint tea, which may aid digestion
If bloating persists beyond 4 weeks or becomes severe, don't wait — contact your GP. Occasionally, bloating can indicate a more serious issue requiring medical attention, such as pancreatitis (very rare but serious).
- 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.
How long does bloating last when starting Mounjaro?
Bloating is most common in the first 4–8 weeks of treatment or after a dose increase. For most people, it improves within 2–4 weeks as their body adjusts to the medication. If it persists beyond 4 weeks or worsens, contact your GP for guidance.
Can I take anti-bloating medication while on Mounjaro?
Over-the-counter remedies like simethicone (which breaks up gas bubbles) are generally safe alongside Mounjaro, but always check with your GP or pharmacist first, as they know your full medical history and other medications. Avoid excessive use of laxatives without medical advice.
Is bloating a sign that Mounjaro isn't working?
No, bloating is actually a sign that Mounjaro is working — it's a recognised side effect caused by the medication's mechanism. Bloating doesn't mean the medication is failing; it's part of the adjustment period. Most people experience reduced appetite and weight loss alongside the bloating, which typically settles with time.
Should I reduce my Mounjaro dose if I'm bloated?
Do not reduce your dose without speaking to your prescriber first. Bloating usually improves as your body adjusts, and reducing the dose may slow your progress. If bloating is severe, contact your GP — they may recommend a slower dose increase or suggest management strategies while you adjust.
Is bloating on Mounjaro the same as bloating on Wegovy?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) can cause bloating because they both slow gastric emptying. However, Mounjaro is a dual GIP and GLP-1 agonist, while Wegovy is GLP-1 only, so the mechanism is slightly different. Some people report less bloating on one versus the other, but experiences vary. Your prescriber can discuss which option might suit you better.
Ready to take control of your weight loss journey?
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