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
Why Am I Gassy On Mounjaro?
Feeling gassy or bloated while taking Mounjaro (tirzepatide) is a common side effect, especially during the first few weeks of treatment. This happens because Mounjaro slows how quickly food moves through your stomach and can cause changes in your gut bacteria as your body adjusts. The good news is that for most people, gas and bloating improve significantly after 4–8 weeks as your digestive system adapts. In the meantime, there are practical steps you can take to reduce discomfort while continuing your weight loss journey with this prescription medication.
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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.
Understanding Gas on Mounjaro and Managing It
Why Mounjaro causes gas: Tirzepatide works by slowing gastric emptying—how quickly food leaves your stomach. This slower digestion can trap gas in your stomach and intestines, leading to bloating and flatulence. Additionally, the reduced appetite means many people eat differently or consume foods they're not used to, which can disturb their gut bacteria balance.
- Gas typically peaks in weeks 2–4 after starting or increasing your dose
- Symptoms often improve significantly by weeks 5–8 as your body adapts
- Staying hydrated and eating slowly can reduce gas production
- Avoiding carbonated drinks, high-fat foods, and artificial sweeteners helps minimise bloating
- Small, frequent meals are easier to digest than large portions
If gas persists beyond 8 weeks or becomes severe, speak to your GP or prescriber. They may suggest dose adjustments or recommend over-the-counter remedies like simethicone. Many people find that gentle walking after meals aids digestion and reduces gas discomfort.
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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.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
Accessing Mounjaro in the UK: Cost and Routes
In the UK, you can access Mounjaro through the NHS specialist tier 3 weight management services (via GP referral) or through private online prescription services. NHS access varies significantly by region and may involve waiting lists of several months. Private access is faster: you complete an online clinical assessment with a UK-licensed prescriber, receive a prescription if appropriate, and collect from a registered pharmacy. Private Mounjaro costs approximately £150–£300 per month depending on your dose and provider, with the KwikPen containing 4 weeks of once-weekly injections.
- 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 gas last when starting Mounjaro?
Most people experience peak gas and bloating in weeks 2–4 after starting or increasing their dose. Symptoms typically improve significantly by weeks 5–8 as your digestive system adapts to tirzepatide. If gas persists beyond 8 weeks, discuss it with your GP or prescriber—dose adjustments or dietary changes may help.
What can I eat to reduce gas while on Mounjaro?
Stick to easily digestible foods: lean proteins, vegetables without skins, rice, bananas, and plain yoghurt. Avoid carbonated drinks, high-fat foods, artificial sweeteners (which ferment in the gut), and raw cruciferous vegetables like cabbage. Eat slowly in small portions, chew thoroughly, and drink water—not sugary or fizzy drinks—to minimise gas production.
How much does Mounjaro cost privately in the UK?
Private Mounjaro costs range from approximately £150–£300 per month depending on your dose. Lower doses (2.5–5 mg) cost less; higher maintenance doses (10–15 mg) cost more. Each KwikPen contains 4 weekly injections. Prices vary between different GPhC-registered private pharmacies, so it's worth comparing.
How do I get Mounjaro on the NHS in the UK?
You'll need referral from your GP to a tier 3 specialist weight management service in your area. NHS eligibility requires a BMI of 30+ or 27+ with weight-related health conditions like diabetes or hypertension. However, NHS availability varies by region and waiting lists can be very long. Your GP can tell you if your local ICB (Integrated Care Board) funds Mounjaro prescriptions.
What's the difference between Mounjaro and Wegovy for gas symptoms?
Both are GLP-1-based medications that slow stomach emptying, so both can cause gas initially. Mounjaro (tirzepatide) is a dual GIP+GLP-1 agonist and may cause slightly different side effect patterns than Wegovy (semaglutide), which is a GLP-1 agonist only. Individual responses vary—what triggers gas in one person may not affect another. Your prescriber can help you choose based on your health profile.
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.