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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Mounjaro and Gas — What You Need to Know
Gas and bloating are common side effects when starting Mounjaro (tirzepatide), a prescription-only weight management injection licensed in the UK. This happens because Mounjaro slows how quickly food moves through your digestive system and changes how your body processes food. While uncomfortable, gas typically improves as your body adjusts to the medication. Understanding what to expect and when to seek advice from your GP helps you manage this side effect confidently.
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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.
Why Mounjaro Causes Gas and Bloating
Mounjaro works as a dual GIP and GLP-1 receptor agonist, activating two hormone pathways that help regulate appetite and blood sugar. One effect is slowed gastric emptying — food moves more slowly from your stomach to your intestines. This can cause gas, bloating, and abdominal discomfort, particularly in the first 4–8 weeks.
Gas may also result from:
- Changes in how your gut bacteria process food as Mounjaro affects digestion
- Swallowing more air if you're eating too quickly despite feeling full
- Reduced food intake overall — smaller meals can ferment differently in your intestines
- Individual sensitivity to the dose and rate of dose titration
These effects are very common (affecting more than 1 in 10 people in clinical trials) and usually decrease significantly after the first 8–12 weeks as your body adapts. Your GP can provide reassurance and practical strategies to manage discomfort during this adjustment period.
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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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Managing Gas and When to Contact Your GP
Practical steps to reduce gas while taking Mounjaro:
- Eat slowly and chew food thoroughly — smaller bites reduce air swallowing
- Choose easily digestible foods: lean proteins, cooked vegetables, white rice, bananas
- Avoid high-fibre foods temporarily — introduce gradually once symptoms improve
- Stay hydrated — drink water between meals, not during
- Limit carbonated drinks, artificial sweeteners, and fatty foods
- Try gentle movement like walking to aid digestion
Contact your GP if gas is severe, persistent beyond 12 weeks, or accompanied by vomiting, severe stomach pain, or changes in bowel habits. These could indicate other issues requiring investigation. Your prescriber can also review whether adjusting your Mounjaro dose titration schedule might help.
- 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 taking Mounjaro?
Gas typically improves significantly after 4–8 weeks as your body adjusts to how Mounjaro slows digestion. By 12 weeks, most people experience substantial improvement. However, some individuals report mild bloating continuing longer. Consistency with dietary adjustments and staying hydrated helps speed resolution.
Does gas mean Mounjaro isn't working?
No. Gas is a normal side effect of how Mounjaro works — it slows gastric emptying, which is part of its weight management mechanism. Gas does not indicate whether the medication will be effective for weight loss. Many people experience gas relief within weeks while continuing to see weight loss benefits.
Should I stop taking Mounjaro if gas is severe?
Do not stop without speaking to your GP or prescriber. Severe gas may indicate a need to adjust your dose titration schedule, change your diet, or rule out other conditions. Your prescriber can help determine whether continuing at your current dose, slowing the titration, or other adjustments are appropriate for you.
Can I use over-the-counter remedies for Mounjaro gas?
Common remedies like simethicone (Buscopan IBS Relief) or peppermint tea may help some people. Always check with your GP or pharmacist before using any over-the-counter product, as some may interact with Mounjaro or other medications you're taking.
Is gas worse with higher Mounjaro doses?
Gas can be more pronounced when first starting Mounjaro or when increasing doses. The dose titration schedule (increasing gradually from 2.5 mg to 15 mg) helps your body adapt. Slower titration may reduce gas severity. Your prescriber can discuss dose adjustment options if gas is problematic.
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.