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 Gassy? Mounjaro vs Wegovy Comparison
Yes, Mounjaro can cause gas and bloating in some people, particularly during the first few weeks of treatment. Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight management injections that can cause digestive side effects, though the mechanisms differ slightly. This guide compares how these GLP-1 and GIP/GLP-1 medications affect digestion and helps you understand what to expect. Always consult your GP or a licensed prescriber before starting either medication, as individual responses vary significantly.
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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.
How Mounjaro and Wegovy Affect Digestion Differently
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two hormone pathways simultaneously. Wegovy (semaglutide) is a GLP-1 receptor agonist only, activating a single pathway. Both slow gastric emptying—the rate food leaves your stomach—which can cause gas, bloating, and indigestion.
In the SURMOUNT clinical trial for Mounjaro, gastrointestinal side effects were very common during titration (dose escalation). In the STEP trials for Wegovy, similar digestive issues appeared. Gas and bloating typically improve within 4–8 weeks as your body adjusts. The dual mechanism of Mounjaro may cause slightly different symptom patterns than Wegovy's single GLP-1 pathway, though individual variation is significant.
- Mounjaro KwikPen: Doses increase weekly from 2.5 mg to maximum 15 mg
- Wegovy: Doses increase weekly from 0.25 mg to maximum 2.4 mg
- Slower titration schedules can reduce initial gas and bloating
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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 Is Better for Digestive Comfort?
There is no straightforward answer—digestive tolerance is highly individual. Some people tolerate Mounjaro's dual mechanism better; others find Wegovy's single GLP-1 action suits them. A UK-licensed prescriber assesses your personal health history, current medications, and any existing digestive conditions to recommend the most suitable option during a clinical assessment.
Practical strategies to minimise gas on either medication include eating smaller, more frequent meals; avoiding high-fat and high-fibre foods initially; staying hydrated; and taking the injection at the same time each week. Your prescriber can also adjust your dose titration speed or pause escalation if gas becomes problematic. Use our free BMI calculator to understand your current weight status, then discuss your options with your GP or prescriber.
- 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 gas than Wegovy?
Not necessarily. Both medications slow gastric emptying and can cause gas, bloating, and indigestion. Mounjaro's dual GIP+GLP-1 mechanism may feel different from Wegovy's single GLP-1 action, but individual tolerance varies greatly. Your prescriber can help determine which suits you better based on your medical history.
How long does Mounjaro gas last?
Most people see digestive side effects improve within 4–8 weeks as their body adjusts. Gas and bloating are most common during the first 2–4 weeks of treatment or when doses are increased. If symptoms persist beyond 8 weeks, discuss this with your prescriber—dose adjustment or slowing titration may help.
Can I prevent gas on Mounjaro or Wegovy?
Yes, several strategies help: eat smaller, more frequent meals; avoid high-fat and high-fibre foods early in treatment; stay well hydrated; and avoid carbonated drinks. Slowing your dose titration schedule can also reduce initial symptoms. Your prescriber can advise on a slower escalation plan if needed.
Is Mounjaro UK prescription-only?
Yes, Mounjaro (tirzepatide) is prescription-only in the UK. You need a clinical assessment from a licensed prescriber before starting. Access is available through NHS specialist weight management services or private online prescribing services following an assessment.
How do I decide between Mounjaro and Wegovy in the UK?
Your prescriber assesses your eligibility, medical history, and individual circumstances to recommend the most suitable medication. Both are effective for weight management when used alongside lifestyle changes. Discuss any concerns about side effects, including gas, during your consultation so your prescriber can tailor your treatment plan accordingly.
Ready to take control of your weight loss journey?
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