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 Pain In Stomach vs Wegovy: What's the Difference?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) can cause stomach pain as a side effect, but the frequency and severity differ between the two medications. Understanding how these dual GIP and GLP-1 receptor agonists compare helps you and your GP make an informed choice about which prescription weight loss injection might be right for you. This guide compares the stomach pain profiles from clinical trials and explains what individual suitability means in UK practice.
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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.
Clinical Trial Data: Stomach Pain Frequency
Mounjaro (tirzepatide) caused abdominal pain in clinical trials, with stomach discomfort reported as a very common side effect (affecting more than 1 in 10 participants). In the SURMOUNT-1 trial, gastrointestinal symptoms including nausea, vomiting, diarrhoea, constipation, and abdominal pain were among the most frequently reported adverse events, particularly during dose titration phases.
Wegovy (semaglutide) also causes stomach pain, similarly classified as very common in clinical trials. The STEP trials showed comparable rates of gastrointestinal disturbance, including nausea and abdominal discomfort. The difference lies in mechanism: Mounjaro's dual GIP and GLP-1 action may affect gastric motility differently than Wegovy's GLP-1-only mechanism, though individual responses vary significantly.
- Mounjaro: Pain often improves as your body adjusts during dose titration
- Wegovy: Stomach symptoms typically resolve within weeks of starting each dose
- Both: Eating smaller, lower-fat meals can help minimise discomfort
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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.
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Which Medication Is Right For You?
Neither Mounjaro nor Wegovy is inherently "better" for stomach pain—individual responses differ significantly, and what causes pain in one person may not affect another. A UK-licensed prescriber will assess your full medical history, current medications, and any previous gastrointestinal issues when recommending which injection suits you. If you've experienced stomach pain with one GLP-1 medication, your prescriber may recommend switching to the alternative, as some patients tolerate one better than the other.
Both are prescription-only medicines requiring clinical assessment before use. Use our free GLP-1 weight loss calculator to explore potential outcomes, and discuss your specific risk factors with your GP or prescriber before starting either medication.
- 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.
Is stomach pain with Mounjaro worse than Wegovy?
Clinical trials show similar rates of abdominal pain for both. Mounjaro's dual GIP+GLP-1 mechanism may cause slightly different gastrointestinal effects than Wegovy's GLP-1-only action, but individual experiences vary widely. Your prescriber can help determine which suits you based on your personal tolerance.
How long does stomach pain last on Mounjaro or Wegovy?
Most gastrointestinal side effects, including stomach pain, typically improve within 1–2 weeks as your body adjusts. Pain may recur temporarily when increasing doses. Persistent or severe pain should be reported to your prescriber immediately, as it can occasionally indicate pancreatitis.
Can I take painkillers with Mounjaro or Wegovy?
Paracetamol or ibuprofen may help manage mild stomach discomfort. However, inform your GP or prescriber before taking any medication alongside your GLP-1 injection, as some medications may interact or affect absorption. Avoid very high doses of NSAIDs without medical guidance.
What should I eat to reduce stomach pain on these injections?
Eat small, frequent meals of bland, low-fat foods—boiled vegetables, white fish, lean chicken, toast, rice. Avoid fatty, spicy, or high-fibre foods initially. Stay hydrated. Sip water slowly rather than drinking large volumes. Ginger tea or peppermint may help. Your prescriber can refer you to a dietitian for personalised advice.
Should I stop taking Mounjaro or Wegovy if I have stomach pain?
Do not stop without medical advice. Mild stomach pain is expected and usually temporary. However, seek urgent medical attention if you experience severe, persistent pain radiating to your back, as this may indicate pancreatitis. Contact your prescriber immediately if pain is unbearable or accompanied by other concerning symptoms. ```
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